Gran-DEM Documentation

The Select Model dialog is the starting point for configuring a simulation in GranDEM. It allows users to activate the Continuous Fluid Phase (CFD), the Discrete Particle Phase (DEM), and define the coupling mechanisms between them. Depending on the selected options, GranDEM can perform pure CFD simulations, pure DEM simulations, or fully coupled CFD-DEM simulations with momentum, heat, and mass transfer.

The LnE multiphase CFD simulator is a multipurpose tool for carrying out both Lagrangian (granular) and Eulerian (Fluid) flow simulations in various flexible combinations. The Eulerian (fluid) flow modelling is done by using the coupled pressure-velocity model that involves fundamentally the continuity Equation and Navier Stokes Equation solved on a 3D grid domain. 

Within the CFD framework this is also called the SIMPLE algorithm that stands for Semi-Implicit Method for Pressure Linked Equation proposed by Spalding and Patankar (1978). Typically, most commercial CFD solvers for unstructured grid domains use the finite volume method where the pressure and velocities are collocated at cell centre positions. However, the formulation used here is a staggered grid approach where the scalars, like pressure is defined at cell centre and vectors like velocity is defined at face centre (or staggered) position. The Single phase Eulerian can be solved with or without heat transfer (energy balance) and multi-component mass transfer.

The Lagrangian particle flow modelling uses the Discrete Element Method (DEM) for treating collision mechanism. The Eulerian fluid flowsolver can be coupled 2-ways for momentum transfer or exchange with discrete particle phase or DEM. Additionally if heat and mass transfer with the fluid phase is to be initiated then it can be done. 

Another feature of Gran-dem is its DEM can be coupled with external software such as ANSYS FLUENT fluid flowsolver. This coupling can be done for all 3 aspects i.e. momentum, heat and mass transfer.

Figure 2.1

Figure 2.1: Select Model dialog showing CFD, DEM, coupling options and external solver exchange paths.

Table 2.1 Field Description

① Continuous Fluid Phase

Purpose

Activates the Eulerian fluid solver.

Usage

Enable this option whenever fluid flow calculations are required.

Typical Applications

• Air flow
• Water flow
• Gas flow
• Fluidized beds
• Pneumatic conveying

② Heat Transfer

Purpose

Solves the energy equation and predicts temperature distribution.

Enable When

• Cooling analysis
• Heating processes
• Furnaces
• Heat exchangers
• Drying simulations

③ Multi Component Mass Transfer

Purpose

Models transport of multiple chemical species.

Applications

• Drying
• Evaporation
• Gas diffusion
• Chemical reactors

④ Discrete Particle Phase

Purpose

Activates the DEM solver.

Applications

• Granular flow
• Powder mixing
• Conveyors
• Crushers
• Hoppers

⑤ Coupling Momentum Transfer

Purpose

Transfers drag and reaction forces between particles and fluid.

Use When

Both CFD and DEM are enabled.

⑥ Coupling Heat Transfer

Allows thermal energy exchange between particles and the surrounding fluid.

Typical examples include particle cooling, heating, combustion, and drying.

⑦ Coupling Mass Transfer

Allows evaporation, condensation, moisture transport, and chemical species exchange between particles and the fluid.

⑧ Path to Exchange (Write)

Specifies the directory where GranDEM exports coupling data for an external CFD solver.

⑨ Path to Exchange (Read)

Specifies the directory from which GranDEM imports updated CFD solution files.

Typical Simulation Configurations

CFD Only

• Continuous Fluid Phase ✔
• DEM ✘

DEM Only

• Continuous Fluid Phase ✘
• DEM ✔

CFD-DEM Coupling

• Continuous Fluid Phase ✔
• DEM ✔
• Momentum Transfer ✔

Fully Coupled Multiphysics

• CFD ✔
• DEM ✔
• Momentum ✔
• Heat ✔
• Mass ✔

1. On the Main UI ‘Select Model’ setting from the left pane. Under the continuous phase drop down menu election for the Eulerian fluid flow method can be made or set off.
2. If Fixed field, single phase Eulerian or single phase External (Fluent) is selected the user can switch on the fluid heat transfer and/or mass transfer model.
3. If the DEM method in discrete particle phase is switched on the user can choose to couple ‘Momentum transfer’, ‘Heat transfer’ and/or ‘Mass transfer’ with the fluid phase (Eulerian) using the switches below it (Refer Fig. 2.1).
4. If the user wants to use this feature ‘momentum transfer’ is mandatory but the remaining 2 can be chosen.
5. If single phase External (Fluent) has been selected in the continuous phase the user should add the path to the exchange directory at the bottom of the left pane Fig. 2.1. This is needed to connect with ANSYS FLUENT and exchange coupling data. 

The flow behaviour of materials is fundamentally characterised by their physical properties. Therefore, material properties of Eulerian fluids (liquid or gas) and Lagrangian particles (liquid or solid) during CFD flow simulations are extremely important while simulating system flow behavior. The Eulerian Fluid phase can be single component or multiple component. Depending on the choices made in select model for species transport components can be added to Eulerian fluids and their physical properties entered the check boxes.

Similarly, the particles properties are added into in a separate section on left pane depending on if DEM has been selected in ‘Select Model’. The particle flow dramatically affect phenomena such as segregation, wettability, heat and mass transfer, etc within process systems. The fundamental properties of particle material needed for DEM simulations are density, viscosity, thermal conductivity, species diffusivity and heat capacity. Properties like viscosity are relevant only when discrete particles are actually droplets or particles are wet. Similarly, properties like thermal conductivity are relevant when heat transfer is considered or simulations are non-isothermal.

1. On the Main UI, select ‘Material Properties’ from the left pane. This causes the component materials adding additional tabs in the middle pane to appear. This consists of the buttons ‘Add component’ and ‘Delete component’. 
2. Using the ‘Add component’ button new components can be added successively which appear one below the other as ‘Component 1’, ‘Component 2’, etc. (Fig. 3.1). 
3. Under each component, check boxes are provided for adding the ‘Component name’ and ‘Molecular Weight’ of the component. It also has a switch called ‘volatile’ indicating if the component is volatile or not and a button called ‘physical properties.
4. The ‘volatile’ switch is switch on for components that can vaporise from the Lagrangian or discrete particles into the surroundings. It is typically switched on for components like water that can vaporize and leave the discrete phase. But for components like fertilizers, aluminum, iron oxide, etc. that do not typically vaporize during DEM simulations it need not be switched on.
5. When the ‘physical properties’ button is clicked (see Fig. 3.2) it opens a tab to enter in the properties ‘density, viscosity, thermal conductivity, species diffusivity and heat capacity’. Note that as discrete particles are in either solid or liquid phase these properties that are to be entered are in one of these phases.
6. If the volatile switch is on, all the above mentioned (point 5) properties are duplicated to add properties in gaseous state as well. This is essential to evaluate process parameters such as vaporization rate, vapor pressure, etc.
7. It also provides for a thermodynamic stability factor (Rm[GU1] ) that gives the stability coefficient between the volatile component and non-volatile component.

Fig. 3.1: The component setting in the middle pane.

1. Add / Delete Component

• Add Component creates a new material component (Component 1, Component 2, Component 3, etc.).
• Delete Component removes the selected material component.
• Multiple components can be defined for multi-component particles.

2. Component Name
Enter the name of the material component.

Examples

• Water
• Sand
• Coal
• Iron Oxide
• Fertilizer
• Com-01

This name is used throughout the simulation and in thermodynamic calculations.

3. Molecular Weight
Specify the molecular weight of the component.

Typical units:

• kg/kmol (or g/mol depending on the software convention)

Examples:

• Water = 18
• Oxygen = 32
• Nitrogen = 28

The molecular weight is used during species transport, evaporation, diffusion, and thermodynamic calculations.

4. Volatile Switch
Enable this switch if the material can evaporate or vaporize.

ON

• Water
• Alcohol
• Solvents

OFF

• Sand
• Iron
• Alumina
• Fertilizer

When enabled, GranDEM additionally considers gaseous-phase properties for the component and computes vaporization-related processes.

5. Physical Properties
Click Physical Properties to define the material properties of the component.

Typical properties include:

• Density
• Dynamic Viscosity
• Thermal Conductivity
• Specific Heat Capacity
• Species Diffusivity

If the component is marked as Volatile, additional gas-phase properties are also required.

6. Thermodynamic Equilibrium (RM Factors)
This table defines the RM (Relative Miscibility / Thermodynamic Stability) Factors between volatile and non-volatile components.

Columns:

• ID
• RM Factor(s)
• RM Value

These values are used during evaporation and multi-component mass transfer calculations.

Example:

7. RM Value
Enter the numerical RM coefficient for each component pair.

This coefficient influences:

• Phase equilibrium
• Evaporation behaviour
• Mass transfer calculations
• Multi-component thermodynamics

8. Eulerian Fluid Properties
This section defines the gas/fluid components used in the Eulerian CFD solver.

Similar to the particle material section, users can:

• Add/Delete gas components
• Specify gas name
• Enter molecular weight
• Define gas physical properties

These components are used for CFD calculations involving airflow, species transport, heat transfer, and coupled DEM-CFD simulations.

9. Gas Physical Properties
Click Physical Properties to define the fluid properties for the selected gas component.

Typical gas properties include:

• Density
• Dynamic Viscosity
• Thermal Conductivity
• Specific Heat Capacity
• Species Diffusivity

These properties are required for solving:

• Navier-Stokes equations
• Heat transfer
• Mass transfer
• Species transport

Fig. 3.2: Insertion of physical properties of individual component without (left) and with volatility (right)

Description of Fields

1. Component Name

Displays the name of the material component whose properties are being edited.

This helps identify the currently selected material component.

2. Density (kg/m³)

Specifies the material density.

Density determines the particle mass and directly influences:

• Particle weight
• Inertia
• Momentum
• Collision behaviour
• Packing characteristics

Typical values

3. Viscosity (kg/ms)

Specifies the dynamic viscosity of the material.

Viscosity represents the internal resistance of the material to deformation or flow.

Higher viscosity results in:

• Greater resistance to motion
• Reduced particle mobility
• Increased damping during flow

Typical values

4. Thermal Conductivity (W/mK)

Defines the ability of the material to conduct heat.

This property is used when Heat Transfer is enabled.

Higher thermal conductivity allows heat to transfer more rapidly through the material.

Typical values

5. Species Diffusivity (kg/s)

Specifies the diffusion property of the material species.

This parameter is used during:

• Multi-component mass transfer
• Species transport
• Evaporation
• CFD-DEM coupled simulations

Higher diffusivity results in faster species transport between phases.

6. Heat Capacity (J/kgK)

Defines the specific heat capacity of the material.

This property determines the amount of heat required to raise the temperature of one kilogram of material by one Kelvin.

It is used in:

• Energy balance calculations
• Heating and cooling processes
• Thermal simulations

Typical values

Volatile Materials

If the Volatile option is enabled for a component in the Material Properties window, the Physical Properties dialog is extended to include additional properties for the gaseous phase.

In this case, users must define both:

• Liquid/Solid Phase Properties
  • Density
  • Viscosity
  • Thermal Conductivity
  • Species Diffusivity
  • Heat Capacity
• Gas Phase Properties
  • Gas Density
  • Gas Viscosity
  • Gas Thermal Conductivity
  • Gas Species Diffusivity
  • Gas Heat Capacity

These additional properties are required for accurately modelling:

• Evaporation
• Vaporization
• Heat transfer
• Mass transfer
• DEM-CFD coupled simulations

The main functionality of system motion is of relevance when DEM simulations need to be performed where the domain motion is also simulated alongside DEM particles. The domain motion here can be of two types namely; vibrational motion and rotational motion. Under this functionality the system domain or Eulerian grid consisting of nodes, cells and faces position changes dynamically with time. This begins from an original position and periodically depending on the type of motion returns to the original position.

In case of vibrational motion, the entire domain including the Eulerian grid nodes, cells and faces move in a vibrational form with an amplitude and a time constant. The vibrational motion also needs to be set with vibrational direction.

In case of rotational motion, the domain including the Eulerian grid nodes, cells and faces move about a position axis at a given fixed rotational speed. 

1. The System Motion module is used to define external motion fields acting on the simulation domain. These motion fields include Gravity, Vibration, and Rotation, allowing users to simulate stationary, vibrating, and rotating systems.
2. To access this module, select System Motion from the left navigation pane. The middle pane displays three tabs:
3. Gravity
4. Vibration
5. Rotation

Fig 4.1: System motion model selection showing the gravity tab.

Gravity

The Gravity tab is used to define the gravitational acceleration acting on particles and fluids during the simulation. Users can enable or disable gravity, specify its magnitude, and define the direction of the gravitational field.

Gravity is applied uniformly throughout the computational domain.

Description of Fields

1. Gravity Enable Switch

The On/Off switch enables or disables gravity during the simulation.

• ON
  • Gravity is included in the governing equations.
  • Particles experience gravitational acceleration.
  • Fluid body forces due to gravity are also considered (when CFD is enabled).
• OFF
  • Gravity is ignored.
  • Useful for zero-gravity or microgravity simulations.

2. Gravity Magnitude (m/s²)

This field specifies the magnitude of gravitational acceleration.

which represents the standard gravitational acceleration on Earth.

Users may specify different values to simulate other environments.

Examples

3. Direction Definition Method

GranDEM provides two methods for specifying the gravity direction.

Vector

Defines gravity using Cartesian vector components.

This method is suitable when the direction is known in terms of X, Y, and Z coordinates.

Angle

Defines gravity using angular coordinates.

This option is useful when gravity direction is easier to express as an angle rather than individual vector components.

4. Direction Components

When Vector mode is selected, the gravity direction is defined using three Cartesian components.

gX

Gravity component along the X-axis.

gY

Gravity component along the Y-axis.

gZ

Gravity component along the Z-axis.

Example

For gravity acting vertically downward in the negative Z direction:

5. Unit Vector

The entered gravity direction is automatically treated as a unit vector.

The software internally normalizes the vector to ensure that only the direction is used while the specified gravity magnitude determines the acceleration.

6. Clear Button

The Clear button resets all direction component fields.

This allows users to quickly define a new gravity direction without manually deleting the existing values.

Working Principle

During simulation, GranDEM computes the gravitational force acting on each particle according to:

Fg=mg\mathbf{F_g}=m\mathbf{g}Fg​=mg

where:

• Fg = gravitational force (N)
• m = particle mass (kg)
• g = gravitational acceleration vector (m/s²)

The gravity vector is obtained from the user-defined magnitude and direction entered in the Gravity tab.

Applications

The Gravity module can be used to simulate:

• Particle settling
• Hopper discharge
• Powder handling
• Granular flow
• Conveyor systems
• Rotating drums
• Fluidized beds
• Sedimentation processes
• DEM-CFD coupled simulations

Vibration

The Vibration tab is used to apply translational vibration to the simulation domain. This feature enables users to simulate systems where particles or fluids are subjected to periodic oscillatory motion, such as vibrating feeders, sieves, conveyors, compaction equipment, and mixing devices.

To use vibration, enable the On/Off switch and specify the vibration amplitude and time constant. During the simulation, the prescribed vibration is applied uniformly to the entire computational domain.

Fig 4.2: System motion model selection showing the vibration tab.

Description of Fields

1. Vibration Enable Switch

The On/Off switch enables or disables vibration during the simulation.

ON

• Vibration is applied to the simulation domain.
• Particle motion is influenced by the specified vibration parameters.
• Suitable for modelling vibrating equipment and oscillatory motion.

OFF

• No vibration is applied.
• Particles move only under the influence of other forces such as gravity, contact forces, drag, and external loads.

2. Amplitude (m)

The Amplitude field specifies the maximum displacement of the vibrating system from its equilibrium position.

A larger amplitude produces greater displacement during each vibration cycle.

Typical examples:

3. Time Constant (s)

The Time Constant defines the characteristic time associated with the vibration motion.

It controls how rapidly the vibration evolves with time and influences the transient response of the system.

Smaller values produce a faster response, while larger values result in a more gradual variation of the vibration.

Rotation

The Rotation tab is used to apply rotational motion to the simulation domain. This feature is particularly useful for modelling equipment such as rotating drums, tumblers, mixers, ball mills, rotary kilns, centrifuges, and rotating reactors.

When enabled, the simulation domain rotates about a user-defined axis passing through a specified point in space. Users can define the rotational speed, the direction of the rotation axis, and the position through which the axis passes.

Fig 4.3: System motion model selection showing the rotation tab.

Description of Fields

1. Rotation Enable Switch

The On/Off switch enables or disables rotational motion during the simulation.

ON

• Rotational motion is applied to the computational domain.
• Particles experience centrifugal and Coriolis effects depending on the rotational speed.
• Suitable for rotating machinery and mixing applications.

OFF

• No rotational motion is applied.
• The simulation behaves as a stationary system unless other motion models are enabled.

2. Angular Speed (rps)

The Angular Speed field specifies the rotational speed of the system.

Higher angular speed increases the rotational velocity and consequently the centrifugal forces acting on the particles.

Typical examples:

3. Axis (Unit Vector)

The Axis section defines the direction of the rotational axis using a unit vector.

The axis direction is specified by three Cartesian components.

X (m)

Defines the X-component of the rotation axis.

Y (m)

Defines the Y-component of the rotation axis.

Z (m)

Defines the Z-component of the rotation axis.

Example

For a drum rotating about the global Z-axis:

For rotation about the X-axis:

The entered values are automatically normalized internally to form a unit vector, ensuring that only the direction of the axis is considered.

4. Position

The Position section specifies a point through which the rotation axis passes.

The coordinates are entered in the global coordinate system.

X (m)

X-coordinate of the rotation axis.

Y (m)

Y-coordinate of the rotation axis.

Z (m)

Z-coordinate of the rotation axis.

Example

If the rotation axis passes through the origin:

5. Clear Button

The Clear button resets all axis and position fields.

This allows users to quickly redefine the rotation axis without manually clearing each input box.

Working Principle

When rotational motion is enabled, GranDEM rotates the computational domain about the user-defined axis at the specified angular speed.

The rotation is completely defined by three parameters:

• Angular Speed
• Rotation Axis
• Rotation Position

During the simulation, particles experience additional inertial effects associated with rotational motion, including:

• Centrifugal force
• Coriolis force (where applicable)
• Rotational acceleration

These effects significantly influence particle trajectories, mixing behaviour, and material transport.

The Discrete element method-based particle tracking is governed by Newton’s law of motion. The dynamic motion of any particle ‘a’, defined vectorially in a 3-D space by position vector ‘r_a’ and mass ‘m_a’, is determined by the sum of the forces acting on the particle. This balance is provided hereby in Eq. 3.1;

                                                                                                (3.1)

Where;  \(F_G\) is the gravity force, \(F_C\) is the contact collision force and  \(F_D\) is the drag force acting on the particle.

1. The Collision Force tab is used to define the contact force model governing interactions between discrete particles during DEM simulations. These parameters determine how particles behave when they come into contact with one another or with solid boundaries.
2. GranDEM uses the Cundall–Strack Contact Model, one of the most widely adopted soft-sphere DEM contact models. This model represents the contact between particles using normal and tangential springs, friction, and damping to simulate realistic collision behaviour.

Fig. 5.1: Particle Model window showing the Collision Force tab.

Description of Fields

1. Collision Force Enable Switch

The On/Off switch enables or disables the collision force model.

ON

• Particle-particle and particle-wall contact forces are calculated.
• DEM collision mechanics are activated.
• Required for most granular flow simulations.

OFF

• Contact forces are ignored.
• Particles pass through one another without physical interaction.
• Mainly intended for testing or specialised simulations.

2. Autoset

The Autoset option automatically computes suitable collision parameters based on the specified particle material properties.

When enabled, GranDEM estimates recommended values for:

• Normal restitution
• Tangential restitution
• Spring stiffness
• Tangential spring stiffness
• Friction coefficients

This feature helps users quickly initialise simulations with physically reasonable parameters.

3. Cundall–Strack Model

GranDEM employs the Cundall–Strack soft-sphere contact model, in which contacting particles are represented by elastic springs and frictional sliders.

The model computes:

• Normal elastic force
• Tangential elastic force
• Sliding friction
• Rolling resistance
• Energy dissipation during impacts

Contact Model Parameters

4. Normal Restitution (Norm.Res.)

The Normal Restitution Coefficient defines the elasticity of collisions in the direction normal to the contact surface.

Higher values cause particles to rebound more strongly after impact.

5. Tangential Restitution (Tang.Res.)

The Tangential Restitution Coefficient controls the recovery of tangential motion after contact.

Lower values produce greater damping of tangential motion during collisions.

6. Spring Stiffness (Spr.Stiff.)

The Spring Stiffness defines the normal contact stiffness between particles.

It controls how much two particles deform during collision.

Higher stiffness values result in:

• Smaller particle overlap
• Shorter collision duration
• Increased numerical stiffness

Lower values permit greater overlap and softer collisions.

7. Tangential Spring Stiffness (T Spr.Stiff.)

The Tangential Spring Stiffness specifies the stiffness of the tangential contact spring.

This parameter influences:

• Tangential force development
• Sliding behaviour
• Particle rolling characteristics

8. Frictional Coefficient (μ_f)

The Friction Coefficient controls sliding friction between contacting surfaces.

Higher values:

• Increase resistance to sliding
• Reduce particle mobility
• Improve particle interlocking

Lower values allow particles to slide more freely.

9. Rolling Friction Coefficient

The Rolling Friction Coefficient defines the resistance to particle rolling.

Higher rolling friction:

• Reduces rolling motion
• Produces more stable particle packing
• Better represents irregular particle shapes

Granulation Parameter

10. Coalescence Threshold

The Coalescence Threshold specifies the minimum condition required for two colliding particles to merge (coalesce) during granulation simulations.

This parameter is primarily used in simulations involving:

• Wet granulation
• Pellet formation
• Agglomeration
• Powder processing
• Pharmaceutical manufacturing

For DEM simulations that do not involve particle growth or agglomeration, this value can generally be left at its default setting.

Working Principle

During each simulation time step, GranDEM detects contacts between particles and computes the interaction forces using the Cundall–Strack contact model. The collision behaviour is governed by:

• Normal restitution coefficient
• Tangential restitution coefficient
• Normal spring stiffness
• Tangential spring stiffness
• Sliding friction coefficient
• Rolling friction coefficient
• Coalescence threshold (for granulation simulations)

These parameters collectively determine how particles collide, rebound, slide, roll, dissipate energy, and, where applicable, merge into larger agglomerates.

Drag Force

The Drag Force model is used when particles interact with a surrounding fluid such as air, water, or gas. As particles move through the fluid, the fluid exerts a resistance force called drag force, which opposes the particle motion.

GranDEM provides several well-established drag force correlations from the scientific literature. The appropriate drag law should be selected based on the flow regime, Reynolds number, particle concentration, and application.

Fig. 5.2: Particle Model – Drag Force

① Drag Force Enable Switch

Purpose

Enables or disables drag force calculations.

Options

• On – Fluid drag force is included in the DEM calculations.
• Off – No drag force is applied to particles.

Recommendation

Enable this option whenever a fluid phase (air, gas, or liquid) interacts with particles.

② Drag Law Selection

This drop-down list allows the user to select the mathematical correlation used to calculate drag force.

Available models include:

• Grace et al.
• Schiller and Naumann
• Ergun and Wen & Yu (1952)
• Beetstra et al. (2007)
• Tang et al. (2014)
• Drag Force-6
• Drag Force-7
• Drag Force-8

Each model has been developed for different particle-fluid systems and operating conditions.

Available Drag Models

Grace et al.

Suitable for:

• Fluidized beds
• Gas-solid systems
• Dense particle suspensions

Provides accurate drag predictions across a wide range of particle Reynolds numbers.

Schiller and Naumann

One of the most widely used drag correlations.

Recommended for:

• Single particle motion
• Dilute suspensions
• Low to moderate Reynolds numbers

Commonly used in CFD-DEM simulations.

Ergun and Wen & Yu (1952)

Designed primarily for:

• Packed beds
• Dense particle assemblies
• Fluidization calculations

Combines the Ergun equation with the Wen-Yu correlation to model drag over different solid volume fractions.

Beetstra et al. (2007)

Recommended for:

• Dense particulate flows
• CFD-DEM coupling
• Gas-solid fluidized beds

Accounts for particle interactions in concentrated suspensions.

Tang et al. (2014)

Suitable for:

• High solid volume fraction flows
• Advanced multiphase simulations
• Improved drag prediction in dense systems

Provides enhanced accuracy for modern DEM-CFD simulations.

Drag Force-6

Custom drag model available within GranDEM.

May be used for specialized research applications requiring alternate drag formulations.

Drag Force-7

Additional empirical drag correlation provided for advanced simulations.

Useful for validating different drag models against experimental data.

Drag Force-8

Alternative drag model intended for specialized particle-fluid interaction studies.

Users should select this model when recommended by project requirements or validation studies.

Selecting the Appropriate Drag Model

Notes

• Drag force calculations are only meaningful when a continuous fluid phase is enabled.
• The selected drag law significantly affects particle velocity, residence time, pressure drop, and fluid-particle momentum exchange.
• Different drag models are optimized for different flow regimes. Users should choose the model appropriate for their application and, where possible, validate simulation results against experimental data or published literature.

The injection of particles into the domain is set up in this functionality. Here a flexible injection system has been provided where user is able to choose from a variety of types of injection depending on requirement. There are 4 main types of injections that can be defined. They are;

Injection type 1: Specific point injection

Injection type 2: Cell centre fixed point injection

Injection type 3: Fixed square grid ordered injection

Injection type 4: Feed channel injection

PARTICLE INJECTION (FL_INJ):

6.1 Injection Initialization – Specific Point Injection

The Specific Point Injection method is used to introduce particles into the computational domain from one or more user-defined locations. Each injection point represents a particle source where particles are generated with specified physical properties, initial velocity, temperature, and composition.

This injection method is suitable for simulations involving:

• Spray nozzles
• Powder feeders
• Material discharge points
• Hopper outlets
• Granular injection into reactors
• Particle dosing systems

The user can define multiple independent injection locations, each having its own particle properties and operating conditions.

Fig. 5.1: Specific Point Injection Settings

1. Specific Point (Enable)

Enables or disables the Specific Point Injection model.

• Yes – Specific Point Injection is activated.
• No – This injection model is ignored during simulation.

2. Number of Injection

Specifies the total number of independent injection points that will be created.

Example:

• 1 → Single injection location
• 5 → Five independent injection sources

3. Add Injections

Creates the specified number of injection entries.

After clicking this button, individual injection configurations become available.

4. Select Injection

Displays the list of all previously created injections.

The user can select an injection for editing or reviewing its properties.

Example:

• Injection 1
• Injection 2
• Injection 3

5. Save

Stores all modifications made to the currently selected injection.

Changes are not permanently saved until this button is pressed.

6. Delete

Removes the selected injection definition from the project.

Deleting an injection permanently removes all associated settings.

Injection Parameters

7. Injection Name

A unique user-defined name used to identify the injection.

Examples:

• Feed Inlet
• Nozzle 1
• Powder Source
• Hopper Outlet

8. Particle Diameter (m)

Defines the diameter of an individual particle.

Unit:

metre (m)

Particle diameter influences:

• Collision behaviour
• Drag force
• Packing characteristics
• Heat transfer
• Mass transfer

9. Parcel Diameter (m)

Defines the diameter of the computational parcel.

A parcel represents a collection of identical particles.

Parcel injection reduces computational cost for simulations involving millions of particles.

10. Number of Particles per Parcel

Specifies how many real particles are represented by a single computational parcel.

means

One computational parcel equals one physical particle.

Larger values are useful for large-scale industrial simulations.

Injection Position

The coordinates define the particle release location.

11. X (m)

X-coordinate of the injection point.

12. Y (m)

Y-coordinate of the injection point.

13. Z (m)

Z-coordinate of the injection point.

Together, these coordinates specify the exact particle injection location within the computational domain.

Initial Velocity

These fields specify the initial velocity of injected particles.

14. Vx (m/s)

Initial velocity along the X-direction.

15. Vy (m/s)

Initial velocity along the Y-direction.

16. Vz (m/s)

Initial velocity along the Z-direction.

These velocity components determine the particle trajectory immediately after injection.

Thermal Conditions

17. Temperature Unit

Allows selection of the temperature unit.

Typical options include:

• Degree Celsius (°C)
• Kelvin (K)

18. Temperature

Specifies the initial particle temperature at the moment of injection.

This parameter is required when heat transfer simulations are enabled.

Composition Mass Fraction

The lower table specifies the chemical composition of injected particles.

Each component previously defined in Material Properties appears automatically.

19. Component ID

Unique identifier of the material component.

20. Component Name

Displays the material name.

Example:

• Water
• Fertilizer
• Sand
• Iron Ore

21. Mass Fraction

Specifies the fraction of each component present within the injected particle.

The total mass fraction of all components must satisfy:

∑iYi=1\sum_i Y_i = 1i∑​Yi​=1

where:

• YiY_iYi​ = Mass fraction of component i

Example:

Total = 1.00

Injection Mode

22. Single / Multiple

Determines how the injection points are interpreted.

Single

A single particle source is used.

Suitable for:

• Single nozzle
• Hopper outlet
• One inlet

Multiple

Allows several independent injection sources within the same simulation.

Useful for:

• Multiple spray nozzles
• Multi-port injectors
• Distributed feeding systems
• Multiple inlet locations

Notes

• Every injection point can have independent particle size, velocity, temperature, and composition.
• Position coordinates should lie within the computational domain.
• The sum of all component mass fractions must equal 1.0.
• When heat transfer is enabled, particle temperature should be specified.
• Multiple injection sources can be configured to simulate complex industrial feeding systems.
• Parcel-based injection significantly reduces computational cost while preserving the physical mass flow rate.

6.2 Injection Initialization – Cell Center Injection

The Cell Center Injection method is used to initialize particles uniformly within a specified three-dimensional region of the computational domain. Unlike the Specific Point Injection, where particles are released from one or more fixed locations, Cell Center Injection automatically generates particles at the center of each computational cell contained within the user-defined bounding box.

This injection method is particularly useful for simulations where particles are initially distributed throughout a volume rather than entering through an inlet.

Typical applications include:

• Fluidized bed initialization
• Packed bed generation
• Bulk powder storage
• Sediment bed formation
• Initial particle distribution in reactors
• Particle settling simulations

Fig. 6.2: Cell Center Injection settings.

Description of Fields

1. Cell Center Injection

The On/Off switch enables or disables the Cell Center Injection model.

ON

• Particles are generated automatically at the center of every computational cell within the specified region.

OFF

• Cell Center Injection is ignored during the simulation.

2. Save

Saves the current Cell Center Injection settings.

Any changes made to the injection parameters should be saved before running the simulation.

Particle Properties

3. Particle Diameter (m)

Specifies the diameter of each injected particle.

The particle diameter influences:

• Particle mass
• Collision behaviour
• Drag force
• Heat transfer
• Packing density

4. Number of Particles per Parcel

Specifies the number of physical particles represented by one computational parcel.

indicates that one parcel represents one physical particle.

Using larger parcel sizes reduces computational cost while maintaining the desired mass loading.

5. Parcel Diameter (m)

Defines the effective diameter of the computational parcel.

Parcel-based injection allows efficient simulation of systems containing millions of particles.

Injection Region (Points)

The injection region is defined by a three-dimensional rectangular bounding box.

Particles are generated only inside this region.

6. Xmin (m)

Minimum X-coordinate of the injection region.

7. Xmax (m)

Maximum X-coordinate of the injection region.

8. Ymin (m)

Minimum Y-coordinate of the injection region.

9. Ymax (m)

Maximum Y-coordinate of the injection region.

10. Zmin (m)

Minimum Z-coordinate of the injection region.

11. Zmax (m)

Maximum Z-coordinate of the injection region.

Together, the six coordinates define the three-dimensional volume in which particles are initialized.

For example:

This creates a rectangular region measuring 0.10 × 0.05 × 0.20 m.

Thermal Properties

12. Temperature Unit

Selects the unit of temperature.

Typical options include:

• Degree Celsius (°C)
• Kelvin (K)

13. Temperature

Specifies the initial temperature of the injected particles.

This field is required when heat transfer calculations are enabled.

Injection Velocity

14. Vm

Specifies the initial magnitude of particle velocity.

Unlike Specific Point Injection, where velocity is entered as separate Vx, Vy, and Vz components, Cell Center Injection uses a single velocity magnitude (Vm) that is applied uniformly to all initialized particles.

Typical values:

Composition Mass Fraction

The lower table specifies the composition of the injected particles.

All material components defined under Material Properties are automatically listed.

15. Component ID

Unique identifier of each material component.

16. Component Name

Displays the name of each material component.

Examples:

• Water
• Sand
• Fertilizer
• Iron Ore

17. Mass Fraction

Specifies the mass fraction of each component in the injected particle.

The sum of all component mass fractions must satisfy:

∑iYi=1\sum_i Y_i = 1i∑​Yi​=1

Example:

Total = 1.00

Working Principle

When Cell Center Injection is enabled, GranDEM identifies all computational cells whose centers lie within the user-defined bounding box. A particle or computational parcel is then initialized at the center of each selected cell using the specified particle diameter, parcel size, temperature, velocity, and composition.

This approach provides a uniform initial particle distribution throughout the selected region and is particularly suitable for simulations that begin with a pre-filled particle bed rather than particles entering from a discrete inlet.

Notes

• The injection region must lie entirely within the computational domain.
• The total mass fraction of all components should equal 1.0.
• Set Vm = 0 m/s when initializing a stationary particle bed.
• Cell Center Injection generates particles based on the computational mesh, ensuring a uniform spatial distribution.
• Larger parcel sizes can significantly reduce computational time for large-scale industrial simulations.

6.3  Injection Initialization – Fixed Grid Injection

The Fixed Grid Injection method is used to inject particles from a uniformly spaced grid of predefined locations within a specified three-dimensional region. Unlike Cell Center Injection, where particles are automatically placed at the computational cell centers, Fixed Grid Injection generates particles at fixed intervals (grid spacing) defined by the user.

This method is particularly useful for creating controlled and evenly distributed particle injections over a specified volume or surface.

Typical applications include:

• Uniform particle distribution
• Spray nozzle arrays
• Multiple feed points
• Powder bed generation
• Bulk material loading
• Reactor initialization
• Granulation studies

Fig. 6.3: Fixed Grid Injection settings.

Description of Fields

1. Fixed Grid Injection

Enables or disables the Fixed Grid Injection model.

Options

• Yes – Fixed Grid Injection is enabled.
• No – Fixed Grid Injection is ignored.

2. Save

Saves the current Fixed Grid Injection settings.

Particle Properties

3. Particle Diameter (m)

Specifies the diameter of each injected particle.

Unit:

metre (m)

The particle diameter affects:

• Particle mass
• Contact force calculations
• Drag force
• Heat transfer
• Particle packing

4. Number of Particles per Parcel

Defines the number of real particles represented by one computational parcel.

Using parcels significantly reduces computational time in large-scale simulations.

5. Parcel Diameter (m)

Defines the effective diameter of the computational parcel.

This value is mainly used when parcel-based particle injection is enabled.

Injection Region

6. Injection Region Coordinates (Xmin, Xmax, Ymin, Ymax, Zmin, Zmax)

These six coordinates define the three-dimensional rectangular region within which particles will be generated on a fixed grid.

• Xmin / Xmax define the minimum and maximum limits along the X-axis.
• Ymin / Ymax define the minimum and maximum limits along the Y-axis.
• Zmin / Zmax define the minimum and maximum limits along the Z-axis.

Together, these coordinates specify the complete injection volume.

7. Temperature Unit

Selects the unit used for particle temperature.

Typical options include:

• Degree Celsius (°C)
• Kelvin (K)

8. Temperature

Specifies the initial temperature of all injected particles.

This parameter is required when heat transfer calculations are enabled.

9. Pitch Distance (Pitch Di)

Defines the spacing between adjacent particle injection points in the fixed grid.

A smaller pitch creates a denser particle distribution, while a larger pitch increases the distance between particles.

Typical unit:

metre (m)

10. Initial Velocity (Vm)

Specifies the initial velocity magnitude assigned to all injected particles.

Unit:

m/s

All particles generated by the fixed grid will initially move with this velocity.

Composition Mass Fraction

The composition table specifies the material composition of the injected particles.

Each material component defined in Material Properties is automatically listed.

11. Component ID

Unique identification number assigned to each material component.

12. Component Name

Displays the name of the material component.

Example:

• Water
• Sand
• Fertilizer
• Iron Ore

13. Mass Fraction

Specifies the mass fraction of each material component.

The sum of all mass fractions must satisfy:

∑Yi=1\sum Y_i = 1∑Yi​=1

Example:

Total = 1.00

Injection Mode

14. Single / Multiple

Determines how particles are injected.

Single

Particles are injected only once during the simulation.

Typical applications:

• Initial bed generation
• One-time particle loading

Multiple

Particles are continuously injected throughout the simulation according to the specified mass flow rate and injection duration.

Suitable for:

• Continuous feeders
• Screw conveyors
• Spray systems
• Industrial material handling

Continuous Injection Parameters

15. Mass Flow Rate (kg/s)

Specifies the mass of particles injected per second.

Higher values result in greater particle loading into the simulation domain.

16. Time Constant (s)

Defines the characteristic time over which the particle injection rate changes.

A larger time constant produces a smoother variation in the injection profile, while a smaller value results in a more rapid response.

17. Start Time (s)

Specifies the simulation time at which particle injection begins.

Before this time, no particles are generated.

18. End Time (s)

Specifies the simulation time at which particle injection stops.

Particle generation ceases after this time.

Working Principle

When Fixed Grid Injection is enabled, GranDEM creates a regular grid of injection points within the user-defined spatial region. The spacing between adjacent points is determined by the Pitch Distance. At each grid location, particles or computational parcels are generated with the specified diameter, velocity, temperature, and material composition. Depending on the selected injection mode (Single or Multiple), particles may be generated once at the start of the simulation or continuously over a specified time interval according to the defined mass flow rate.

Applications

The Fixed Grid Injection model is commonly used for:

• Uniform particle bed generation
• Multiple nozzle arrays
• Powder coating simulations
• Granulation processes
• Fluidized beds
• Particle distribution studies
• Continuous feeding systems
• Industrial reactor simulations

Notes

• Ensure that the defined injection region lies within the computational domain.
• The Pitch Distance should be selected carefully to avoid particle overlap.
• The sum of all component mass fractions must equal 1.0.
• Single mode is generally used for initialization, whereas Multiple mode is intended for continuous particle feeding.
• The Mass Flow Rate, Start Time, and End Time parameters are only applicable when continuous (Multiple) injection is selected.

6.4 Injection Initialization – Channel Injection

The Channel Injection method is designed for simulations in which particles are continuously introduced through one or more channels or inlet locations. Unlike Specific Point Injection, which releases particles from a single location, or Fixed Grid Injection, which distributes particles over a predefined grid, Channel Injection models particle flow through a channel with specified flow conditions.

This injection model is suitable for:

• Screw feeders
• Pipe and duct flows
• Conveyor discharge systems
• Hopper outlets
• Pneumatic conveying
• Powder feeding systems
• Continuous industrial processes

Each channel can be configured independently with its own particle properties, injection location, velocity, mass flow rate, and composition.

Fig. 6.4: Channel Injection settings.

Description of Fields

1. Channel Injection

Enables or disables the Channel Injection model.

Options

• Yes – Channel Injection is enabled.
• No – Channel Injection is ignored during the simulation.

2. Number of Channels

Specifies the total number of independent particle injection channels.

Example:

• 1 → Single inlet channel
• 4 → Four independent injection channels

3. Add Channel

Creates the specified number of channel injection entries.

Each channel can later be configured independently.

4. Select Channel

Displays the list of all previously created channels.

Select a channel to edit or review its parameters.

5. Save

Stores the current settings for the selected channel.

6. Delete

Deletes the selected channel and all associated injection parameters.

Injection Properties

7. Injection Name

A user-defined name used to uniquely identify the injection channel.

Examples:

• Channel-1
• Hopper Outlet
• Feed Pipe
• Pneumatic Inlet

8. Particle Mean Diameter (m)

Defines the average particle diameter used for particle generation.

This value represents the mean size of particles injected through the channel.

9. Standard Deviation (SD) Diameter

Specifies the standard deviation of the particle diameter distribution.

A value of:

• 0 produces particles of identical size.
• Greater than 0 generates particles with a size distribution around the mean diameter.

This parameter is useful for modelling realistic polydisperse particle systems.

10. Number of Particles per Parcel

Defines the number of physical particles represented by a single computational parcel.

Parcel injection reduces computational cost for simulations involving large numbers of particles.

11. Parcel Diameter (m)

Specifies the effective diameter of the computational parcel.

12. Start Time (s)

Specifies the simulation time at which particle injection begins.

Before this time, no particles are injected.

13. End Time (s)

Specifies the simulation time at which particle injection stops.

Channel Parameters

14. Channel Position and Velocity

These fields define the spatial location and initial flow conditions of the channel.

The parameters include:

• X, Y, Z (m) – Coordinates of the channel inlet location.
• Vm (m/s) – Magnitude of the particle injection velocity.
• Vx, Vy, Vz (m/s) – Velocity components in the X, Y, and Z directions.
• Pitch Distance (Pitch Di) – Spacing between adjacent particles during injection when multiple particles are generated across the channel.

Together, these parameters determine the position and direction of particle flow entering the computational domain.

15. Clear

Resets the channel position and velocity values to their default state.

Flow Parameters

16. Mass Flow Rate (kg/s)

Specifies the mass of particles injected per second through the channel.

Increasing the mass flow rate results in a greater quantity of particles entering the simulation domain.

17. Time Constant (s)

Defines the characteristic time governing the variation of the particle injection rate.

Larger values produce smoother transitions, while smaller values result in a more rapid change in the injection profile.

Thermal Properties

18. Temperature Unit

Selects the unit used to specify particle temperature.

Typical options include:

• Degree Celsius (°C)
• Kelvin (K)

19. Temperature

Defines the initial temperature of particles injected through the channel.

This parameter is required when heat transfer simulations are enabled.

Composition Mass Fraction

The lower table defines the material composition of the injected particles.

Each component created under Material Properties is automatically displayed.

20. Component ID

Unique identification number assigned to each material component.

21. Component Name

Displays the name of the material component.

Examples include:

• Water
• Sand
• Fertilizer
• Iron Ore

22. Mass Fraction

Specifies the mass fraction of each component present in the injected particles.

The total mass fraction of all components must satisfy:

∑iYi=1\sum_i Y_i = 1i∑​Yi​=1

Example:

Total = 1.00

Working Principle

When Channel Injection is enabled, GranDEM generates particles through one or more user-defined channels. Each channel acts as a continuous particle source with independently specified location, particle size distribution, velocity, mass flow rate, temperature, and composition. Particles are injected only during the defined time interval (Start Time to End Time) and follow the prescribed flow conditions throughout the simulation.

Applications

Channel Injection is commonly used for:

• Continuous powder feeding
• Pneumatic conveying systems
• Screw conveyors
• Pipe and duct transport
• Hopper discharge
• Granular material processing
• Industrial reactors
• Chemical process simulations

Notes

• Multiple channels can be configured within the same simulation.
• The Particle Mean Diameter and Standard Deviation enable realistic particle size distributions.
• Ensure that the total Mass Fraction equals 1.0.
• The Mass Flow Rate and Time Constant should be selected based on the desired injection profile.
• Channel positions must lie within the computational domain or at valid inlet boundaries.

1. On the UI upper pane, select ‘Fluid flowsolver’. This gives the selection pane on the left pane to make fluid flowsolver model choices and settings as shown in Fig. 8.1.
2. The selections include Method (compressible or incompressible), Scheme (implicit or explicit), viscosity (Laminar or any turbulence model), convective upwind scheme and linear solver.

The unstructured grid domain elements consist of cell external faces that may have been designed to have both external and internal boundaries. The boundaries are defined limits of the domain that can have or represent different conditions for the finite domain. Some of the conventional boundary types defined across CAE formats is listed in table 1. Typically in pressure-velocity based CFD solvers the boundary conditions are imposed on pressure, normal and tangential velocities. The table provides the settings for these conditions for various boundaries. The suffix ‘b’ represents the boundary cell condition and suffix ‘c1’ represents the first internal cell to boundary. In case of vector variables normal and tangential direction vector variables are represented as suffix ‘n’ and ‘t’.

1. On the UI upper pane, select ‘Boundary condition’. This gives the selection pane on the left pane to make fluid flowsolver model choices and settings as shown in Fig. 8.1.
2. The selections include Method (compressible or incompressible), Scheme (implicit or explicit), viscosity (Laminar or any turbulence model), convective upwind scheme and linear solver.

 The execute is the final property to be edited before running a simulation. Fig. 9.1 shows the middle pane that is observed on clicking the Execute in the left pane. Here the output settings, time step settings, end time settings and autoload visualization settings are made. The time step size and DEM time step size are related where the DEM time step size needs to be integer greater than 1. The DEM time step here represents the individual time step over which collision particle tracking integration is performed. However, updating of all other forces is performed at the end of time step size only. This is simply because typically in DEM simulations the collision tracking needs to be refined depending on spring dashpot collision time limitations. Therefore, the time step size for other force updation is typically some factor higher than the DEM collision time step size.  The other important variable setting is the number of timestep simulation and end time which are both related. Hence they autoset when the other is changed.

1.  
2.  
3. The output path and output time interval needs to be set using the check boxes at the top. The output path is the path where the output data will be written.
4. Check boxes for time step size, DEM steps/Time step, Number of time step simulations and End time have been provided in the center of the middle pane with the heading ‘Simulation time settings’.

GranDEM Engine Execute

The GranDEM Engine Execute window is the final stage before starting a simulation. It allows the user to define the simulation output location, numerical time settings, execution options, visualization preferences, and monitoring controls. Once all required model settings have been completed, this window is used to execute the DEM or CFD-DEM simulation.

Fig. X.X: GranDEM Engine Execute Window

Field Description

1. Output Path (Write)

Specifies the directory where all simulation output files will be stored.

The generated files may include:

• Particle data
• Flow field data
• Restart files
• Log files
• ParaView visualization files
• Temporary solver files

Use the browse (...) button to select the desired output folder.

2. Output Time Interval (No. of Time Steps)

Defines how frequently simulation results are written to disk.

For example,

• Output Interval = 10

means simulation data will be saved every 10 computational time steps.

Smaller intervals produce more output files but require additional storage.

Larger intervals reduce disk usage but provide fewer intermediate results.

Simulation Time Settings

3. Time Step Size (s)

Defines the physical time represented by one computational time step.

Smaller time steps provide

• better numerical stability
• higher solution accuracy

but require longer computation times.

4. DEM Steps / Time Step

Specifies the number of DEM calculations performed within each CFD time step.

This parameter is mainly used for coupled CFD–DEM simulations.

5. Total Number of Time Steps

Defines the total number of computational iterations performed.

6. End Time (s)

Specifies the total physical duration of the simulation.

The solver automatically terminates once this time is reached.

7. File Name Initial

Defines the filename prefix for all generated simulation files.

Execution Controls

8. Execute

Starts the simulation using all specified settings.

Before execution, ensure that

• Geometry has been created.
• Materials have been assigned.
• Injection conditions are defined.
• Force models are selected.
• Solver parameters are complete.

Visualization Options

9. ParaView Auto Load

Automatically launches ParaView after completion of the simulation or whenever output files become available.

When enabled, users can immediately visualize

• Particle motion
• Fluid fields
• Velocity vectors
• Temperature contours
• Pressure distributions

without manually opening ParaView.

10. Restart Switch

Enables simulation restart functionality.

When activated, the solver reads previously saved restart files and continues the simulation from the last saved state instead of beginning from time zero.

This is particularly useful for

• long simulations,
• interrupted simulations,
• extending previously completed analyses.

11. Show Graphical Data

Displays live graphical updates while the simulation is running.

Typical information includes

• particle movement,
• convergence history,
• solver progress,
• computational status.

Disabling this option may slightly improve execution speed on slower computers.

Output Management

12. Clear Output

Deletes previously generated simulation output files from the selected output directory.

This option is useful before starting a fresh simulation to avoid mixing old and new result files.

13. Clear Response

Clears the solver response and console messages displayed within the execution window.

Only the displayed log is removed; simulation files remain unchanged.

Solver Response Window

The large console area displays real-time execution messages generated by the solver.

Typical information includes

• simulation initialization,
• mesh loading,
• material loading,
• solver progress,
• iteration status,
• warnings,
• numerical errors,
• successful completion message.

This console is the primary location for diagnosing simulation problems.

Progress Bar

The progress bar at the bottom of the window indicates the current completion percentage of the simulation.

The progress bar gradually increases until the simulation reaches 100%, indicating successful completion.

Workflow

A typical execution workflow is:

1. Select the output directory.
2. Specify the output writing interval.
3. Define the simulation time step size.
4. Set the number of DEM steps per CFD time step.
5. Enter the total simulation time or end time.
6. Provide a filename prefix.
7. Enable optional visualization or restart features if required.
8. Click Execute to start the simulation.
9. Monitor the solver messages and progress bar until completion.
10. Visualize the generated results in ParaView or other supported post-processing tools.

Graphical Data – Residual Graph

The Residual Graph tab is used to monitor the convergence of the numerical solution during CFD simulations. A residual represents the error remaining in the governing equations after each solver iteration. As the simulation progresses, these residual values should decrease, indicating that the solution is converging toward a stable state.

Field Description

1. Show Residual Graph

Description:
This switch enables or disables the real-time display of the residual convergence graph during the simulation.

Purpose:

• Displays the convergence history while the solver is running.
• Helps monitor whether the solution is converging properly.
• Useful for identifying unstable or diverging simulations.

Options

• On – Residual graph is displayed and updated continuously.
• Off – Residual graph is hidden.

2. Residual Iterations History

Description:
Specifies the number of recent solver iterations to display in the residual graph.

Purpose:

• Controls the size of the convergence history shown.
• A larger value provides a longer history of convergence.
• A smaller value focuses on the most recent iterations.

Typical Value

20

This displays the residual values for the last 20 solver iterations.

Residual Graph

When enabled, the graph typically plots:

• Continuity residual
• X-Momentum residual
• Y-Momentum residual
• Z-Momentum residual
• Energy residual (if heat transfer is enabled)
• Species residuals (if mass transfer is enabled)

The residual values are plotted against the solver iteration number, allowing users to evaluate convergence throughout the simulation.

Interpretation of Residual Graph

Fig. 9.1: The Execute selection from left tab showing the input setting details in the middle pane.

1. Further, a setup for auto paraview visualisation loading is provided so that the user can get an auto visualization of the data while the simulation is running. This feature can be switched on by the user using the ‘Paraview Auto Load’ switch while setting the autoload timings using the check boxes besides ‘Time Interval’.

In the event of a simulation crash or end of simulation, the user can also restart the simulation directly from where it stopped. This can be done by first switching on the restart switch and setting the time of restart.

 In the upper left corner of the UI interface is provided with a series of selection for miscellaneous operations and features like FILE, EDIT, SOURCE, etc. The ‘FILE’ selection has options like ‘Open’, ‘Open Mesh File’, ‘Save’, ‘Save As’ and ‘Exit’. The GRANDEM UI ‘Open’ feature can be used to import any standard Grandem case file ‘.gdm’. Similarly, it can also be used to save case ‘.gdm’ file including with password protection. The mesh file can be used to import standard fluent mesh ‘.msh’ file and replace it into the model settings.

Fig 10.1: Selection within ‘FILE’

 This selection on the left pane is used after a simulation run has completed and output result data is available for paraview post-processing and visualization study. On selecting this the middle pane appears as shown in Fig. 11.1. Here in this feature various data type files can be loaded into and viewed in paraview. This includes .cgns, .vtk and .cas fluent files for the grid and fluid data while .vtu files for the particle data. 

In the middle pane 3 main buttons have been provided to start paraview, reset paraview and delete script. Below this are 4 tabs each having their individual post processing functionalities. The first tab is ‘Grid view’ tab for loading grid and fluid data. The second tab is ‘Particle view’ tab for loading particle data files. The third tab is ‘Multiple View’ tab used for expanding to multiple views of the prevailing view to show velocity field, thermal field and species field.

The Grid View tab is used to visualize the computational mesh (grid) generated for the simulation. It provides options to automatically load the simulation files into ParaView and display the computational domain using different visualization modes.

Grid View is primarily used to inspect the mesh quality, verify imported geometry, and examine internal cross-sections before analyzing simulation results.

Fig. 11.1: ParaView AutoScript – Grid View

Field Description

1. Run ParaView

Launches ParaView automatically and executes the generated visualization script. The selected simulation files are loaded without requiring manual import.

2. Reset ParaView

Resets the current ParaView visualization to its default state. Previously loaded objects, filters, and display settings are removed.

3. Delete Script

Deletes the automatically generated ParaView Python script. A new script will be generated the next time visualization is requested.

4. Grid View

Displays the computational mesh (grid) of the simulation domain. This view is mainly used to inspect the generated mesh and geometry before viewing particle or flow results.

5. Particle View

Switches to the particle visualization interface where Lagrangian particles can be displayed and analyzed.

6. Multiple View

Opens multiple visualization windows simultaneously, allowing different datasets or viewpoints to be observed together.

7. Save

Saves the current visualization configuration, including selected options and display settings, for future use.

8. Load CGNS

Loads simulation results stored in the CGNS (CFD General Notation System) format into ParaView.

Typical use:

• Structured CFD datasets
• Flow field visualization
• Pressure, velocity and temperature contours

9. Load VTK

Loads simulation data stored in the VTK (Visualization Toolkit) format.

This format is commonly used for:

• DEM particle results
• Volume data
• Surface meshes
• Scalar and vector fields

10. Load CAS

Loads Fluent mesh or case files (.cas) into ParaView for visualization.

This option is useful when GranDEM is coupled with ANSYS Fluent or when Fluent-generated meshes need to be inspected.

11. 3D View

Enables full three-dimensional visualization of the computational grid.

When enabled, the complete geometry is rendered in 3D, allowing the model to be rotated, zoomed, and inspected from any viewing angle.

12. Opacity (3D View)

Controls the transparency of the 3D computational mesh.

• 0 → Completely transparent
• 1 → Completely opaque

Lower opacity values allow internal regions of the mesh to become visible.

13. Slice View

Displays a two-dimensional cross-sectional slice through the computational domain.

Slice View is useful for examining:

• Internal mesh quality
• Pressure distribution
• Velocity contours
• Temperature fields
• Concentration profiles

without hiding the interior of the model.

14. Opacity (Slice View)

Controls the transparency of the slice plane displayed in ParaView.

Increasing opacity makes the slice easier to observe, while lower values allow the surrounding geometry to remain visible.

15. Normal Direction (X, Y, Z)

Defines the orientation of the slicing plane.

The slice plane is positioned perpendicular to the specified normal vector.

Examples:

• (1, 0, 0) → Slice normal to the X-axis (YZ Plane)
• (0, 1, 0) → Slice normal to the Y-axis (XZ Plane)
• (0, 0, 1) → Slice normal to the Z-axis (XY Plane)

Custom vector values can also be specified to create slices at arbitrary orientations.

Working Procedure

1. Open ParaView AutoScript → Grid View.
2. Choose the desired simulation file format (CGNS, VTK, or CAS).
3. Enable 3D View to visualize the complete computational mesh.
4. Adjust the Opacity to inspect internal mesh regions if required.
5. Enable Slice View to create a cross-sectional view of the model.
6. Specify the Normal Direction (X, Y, Z) to define the orientation of the slice.
7. Click Run ParaView to automatically launch ParaView and load the selected dataset.

Particle View

The Particle View tab in the ParaView AutoScript module is used to visualize DEM particle results generated during a GranDEM simulation. It provides two methods for loading particle data depending on how the simulation results are stored.

Fig. 11.2: ParaView AutoScript – Particle View

Fields Description

1. Load VTU Data (using PVD)

Description:
Loads particle data using a PVD (ParaView Data Collection) file. The PVD file references all VTU files generated during the simulation and automatically organizes them into a time series.

Purpose:

• Loads all simulation time steps at once.
• Enables animation of particle motion.
• Automatically updates the timeline in ParaView.
• Recommended for transient simulations with multiple output files.

Typical Use:

Use this option after completing a simulation when multiple VTU files have been generated for different time steps.

2. Load VTU Data (Direct)

Description:
Loads an individual VTU (VTK Unstructured Grid) file directly into ParaView without requiring a PVD file.

Purpose:

• Opens a single simulation result.
• Useful for inspecting one specific time step.
• Faster when only one output file needs to be visualized.
• Suitable for debugging or post-processing individual datasets.

Typical Use:

Use this option when viewing a single VTU file or when a PVD file is not available.

Recommended Workflow

1. Run the DEM simulation in GranDEM.
2. Generate particle output files (VTU/PVD).
3. Open ParaView → Particle View.
4. Select one of the following options:
   • Load VTU Data (using PVD) for complete time-dependent visualization.
   • Load VTU Data (Direct) for viewing a single particle dataset.
5. Analyze particle trajectories, distribution, velocity, collisions, and other DEM results in ParaView.

Multiple View

The Multiple View tab allows users to create multiple visualization windows in ParaView simultaneously. This feature enables different simulation variables to be displayed side-by-side, making it easier to compare flow behavior, temperature distribution, and species concentration within the same simulation.

Multiple View is particularly useful during post-processing when several physical phenomena need to be analyzed together.

Fig. 11.3: ParaView AutoScript – Multiple View

Field Description

1. Create Multiple Views

Description:
Creates multiple synchronized visualization windows in ParaView.

Purpose:

• Displays several simulation results simultaneously.
• Allows comparison of different physical quantities.
• Improves post-processing efficiency.
• Eliminates the need to repeatedly switch between variables.

Typical Usage:

After selecting the desired visualization options, click Create Multiple Views to automatically generate the corresponding ParaView layout.

2. Velocity Field View

Description:
Enables visualization of the fluid velocity field.

Purpose:

Displays:

• Velocity magnitude
• Velocity vectors
• Flow direction
• Flow patterns
• Recirculation zones
• Vortices

Applications:

• Fluid flow analysis
• CFD verification
• Mixing studies
• Pneumatic conveying simulations
• Particle-fluid interaction analysis

3. Thermal View

Description:
Enables visualization of temperature distribution within the simulation domain.

Purpose:

Displays:

• Temperature contours
• Thermal gradients
• Heat transfer regions
• Hot spots
• Cooling zones

Applications:

• Heat transfer simulations
• Drying processes
• Combustion analysis
• Thermal management studies
• CFD-DEM heat transfer investigations

4. Species View

Description:
Enables visualization of species concentration or mass fraction distribution.

Purpose:

Displays:

• Species concentration contours
• Mass fraction distribution
• Diffusion behavior
• Mixing characteristics
• Mass transfer regions

Applications:

• Multicomponent flow simulations
• Gas-solid reactions
• Drying processes
• Evaporation studies
• Chemical transport simulations

Working Procedure

1. Open ParaView → Multiple View.
2. Enable one or more visualization options:
   • Velocity Field View
   • Thermal View
   • Species View
3. Click Create Multiple Views.
4. ParaView automatically generates separate synchronized windows.
5. Rotate, zoom, and inspect results simultaneously across all selected views.

Advantages of Multiple View

• Simultaneous comparison of multiple variables.
• Faster interpretation of simulation results.
• Better understanding of coupled physical phenomena.
• Useful for CFD, DEM, and CFD-DEM simulations.
• Supports advanced engineering analysis and reporting.

Example

For a CFD-DEM drying simulation:

This allows the engineer to observe how airflow affects heat transfer and moisture removal at the same time.

Save

The Save tab of the ParaView AutoScript module provides options for exporting simulation visualizations and managing camera positions. It allows users to save animations of transient simulations and store predefined camera orientations for consistent visualization and reporting.

Fig. 11.3: ParaView AutoScript – Save View

Field Description

1. Save Animation

Description:
Exports the currently loaded simulation as an animation file using the visualization settings defined in ParaView.

Purpose:

• Creates an animation of the simulation.
• Captures particle movement and fluid flow over time.
• Generates presentation-quality videos.
• Useful for reports, publications, and demonstrations.

Output

Typical output formats include:

• AVI
• MP4
• Image sequence (PNG/JPEG)

(depending on the ParaView export configuration)

2. Frame Rate

Description:
Specifies the number of animation frames displayed per second (FPS).

Purpose:

• Controls the playback speed of the exported animation.
• Higher frame rates produce smoother animations.
• Lower frame rates create slower playback.

Typical Values

Camera Angles

The Camera Angles section allows users to save and reuse predefined camera positions for consistent visualization.

3. Camera Angle Selection

Description:
Displays a list of previously saved camera positions.

Purpose:

• Select an existing camera orientation.
• Reuse the same viewing angle across different simulations.
• Maintain consistent figures for reports and publications.

4. Get

Description:
Retrieves the currently selected camera angle from the list.

Purpose:

• Loads the saved camera parameters.
• Prepares the selected view for application.

5. Save Camera Angles

Description:
Stores the current ParaView camera position and orientation.

Purpose:

• Saves camera location.
• Saves viewing direction.
• Saves zoom level.
• Saves focal point.

This allows the same viewpoint to be reused later.

6. Apply Camera Angles

Description:
Applies the selected saved camera angle to the current visualization.

Purpose:

• Restores a previously saved viewpoint.
• Ensures identical viewing orientation across multiple simulations.
• Produces consistent screenshots and animations.

Working Procedure

1. Open ParaView → Save.
2. Adjust the visualization to the desired viewpoint.
3. Click Save Camera Angles to store the current camera position.
4. Select the desired Frame Rate for animation playback.
5. Click Save Animation to export the simulation.
6. For future simulations, choose a saved camera angle and click Apply Camera Angles to reproduce the same visualization.

Advantages

• Generates high-quality simulation animations.
• Produces consistent camera views across different projects.
• Simplifies report and presentation preparation.
• Reduces manual adjustment of camera orientation.
• Improves reproducibility of visualization results.

1. Check if paraview has been started. If not start paraview by clicking the button ‘Run Paraview’.
2. The first tab ‘Grid view’ can be seen in Fig. 9.1 where 3 buttons have been provided to load either vtk, cgns or cas files. By selecting the check box ‘3D view’ and/or ‘Slice view’ Opacity and slice plane direction can be set before loading.
3. When any of the ‘load’ button is clicked a selection dialog box opens to browse to the folder that contains the data files. Browse to the location folder and select the folder to press ok. This loads the data files into paraview.
4. Move to the ‘Particle View’ tab where on clicking Load VTU button a dialog box opens to browse the data folder location. Browse to the data file location where .pvd file can be located. Select the .pvd file and click ‘open’. This loads particle data files.
5. The next tab is ‘Multiple view’ tab that is utilized when multiple view are to be created simultaneously. This tab has the button ‘Create Multiple views’ (Fig. 9.2) that on clicking creates 4 render views.
6. This tab further has check boxes for ‘velocity field view’, ‘thermal view’ and ‘species view’ all of which can be selected based on user requirement. The ‘Apply view’ button sets up the parallel views of the selected views in the check boxes.
7. The ‘Save’ tab has the functionality to save animations after setting frame rate for the video as show in Fig. 9.3. Besides, this tab also has camera angles saving functionality that sets and saves camera view angles with specific names by clicking the ‘Save Camera Angles’ button.
8. The saved camera angles can be used to select from the drop down menu. When the ‘Apply Camera Angles’ button is used the selected camera angle view is shown or presented. This button can be used for resetting back to a specific angle that the user wants to set.