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5.10.3 Boundary Conditions

The boundary condition attributes for the Particle apply to Boundaries. The options also apply to Interfaces for which the Flow module is Blanked on one side of the interface, creating, in effect, a boundary.

The boundary conditions and associated Particle parameters are specified as follows:

  • Geometric Entities Panel > Boundaries > [Desired Boundary]
  • Properties Panel > Model Tab > Particle
  

Figure 5.222 - Particle boundary conditions

The treatment of particles or streaklines at a Boundary are specified in three ways that are:

 

 

 

 

Figure 5.223 - Particle

Open

ClosedDescription

The Open boundary condition allows the streamline to enter/exit the domain. An Open boundary typically corresponds to a Flow module Inlet or Outlet, but can apply to other type Flow boundary as well.

Particles can be released at an open boundary by setting Release Particle to Yes. Several additional options like Release Frequency, Random Release, Radius of Particles, Release Position, and Initial Velocity are specified for the treatment of the dynamics of particles or streaklines at a boundary.

  

Figure 5.224 - Open Boundary Conditions

Wall

ClosedDescription

Particles can be released at a wall boundary by setting Release Particle to Yes. Several additional options like Release Frequency, Random Release, Radius of Particles, Release Position, and Initial Velocity are specified for the treatment of the dynamics of particles or streaklines at a boundary.

  

Figure 5.225 - Wall boundary conditions
Particle Wall Model

This specifies the behavior of particles or streaklines at a wall boundary. This option is only relevant and available for particles with mass, i.e. Has Mass. For Massless particles, the particle would follow the streamline along the walls.

 

 

 

 

Figure 5.226 - Wall model

The Particle Wall model has the following models:

  1. Perfect Bounce: Particles or streaklines reflects from a wall with the same incident angle and energy. The momentum and kinetic energy of the particle is perfectly conserved, and the angle of incidence is equal to the angle of reflection in this model.
  2. Stick: Particles or streaklines stick to the wall.
  3. Partial Bounce: Particles or streaklines reflect from a wall with a loss in Normal Energy Loss and/or Tangential Energy Loss based on user input.
    • Normal Energy Loss specifies the loss of the normal component of kinetic energy of a particle or streakline hitting a wall boundary with Partial Bounce.
    • Tangential Energy Loss specifies the loss of the tangential component of kinetic energy of a particle or streakline hitting a wall boundary with Partial Bounce.
    • Maximum Normal Velocity: Any particle with a magnitude of its normal velocity greater than the value specified will bounce at the wall boundary.
    • Minimum Normal Velocity: Any particle with a magnitude of its normal velocity less than the value specified will bounce at the wall boundary.

    If the particle’s normal velocity is in between the Maximum Normal Velocity and Minimum Normal Velocity, it will stick to the wall.

     

     

     

     

    Figure 5.227 - Particle wall model (Partial Bounce)

     

    Note: Normal Energy Loss and Tangential Energy Loss is input in terms of the fraction lost (e.g. 1.0 implies a total loss of normal energy). Normal Energy Loss and Tangential Energy Loss greater than 1.0 will be reset to 1. The Normal Energy Loss is a required input for a Wall boundary.

  4. User Defined: User specified behavior of particles or streaklines at a wall boundary.
Erosion Model

This specifies the model to estimate the erosion due to particle impact at a wall boundary. This option is only relevant and available for particles with mass, i.e. Has Mass.

The Erosion model has the following models:

  1. Finne: The Finne model enables the user to specify the Model Constant, Wall Material Density, Velocity Exponent and Vicker Hardness. They can also be specified using the Expression Editor.
  2. Zhang: The Zhang model enables the user to specify the Model Constant, Wall Material Density, Velocity Exponent, Brinell Hardness and Shape Factor. They can also be specified using the Expression Editor.
  3. Oka: The Oka model enables the user to specify the Model Constant, Wall Material Density, Vicker Hardness, Reference Impact Velocity and Reference Particle Diameter. They can also be specified using the Expression Editor.
  4. DNV: The DNV model enables the user to specify the Model Constant, Wall Material Density and Velocity Exponent. They can also be specified using the Expression Editor.
  5. Mansouri: The Mansouri model Enables the user to specify the Model Constant, Wall Material Density, Velocity Exponent, Vicker Hardness, Brinell Hardness and Shape Factor. They can also be specified using the Expression Editor.
  6. Grant-Tabakoff: The Grant-Tabakoff model enables the user to specify the Model Constant, Wall Material Density, Velocity Exponent and Reference Angle. They can also be specified using the Expression Editor.
  Note: The Model Constant is a factor that multiplies the erosion rate. It is set to 1 by default for all erosion models and can be modified if needed.
 
 

Figure 5.228 - Erosion models

Symmetry

ClosedDescription

Symmetry at a boundary causes particle or streaklines to reflect at the boundary. This module typically corresponds to a symmetry boundary in the Flow module.

Particles can be released at a symmetry boundary by setting Release Particle to Yes. Several additional options like (Release Frequency, Random Release, Radius of Particles, Release Position, and Initial Velocity) are specified for the treatment of the dynamics of particles or streaklines at a boundary.

 

Figure 5.229 - Symmetry boundary conditions
Release Particle

Particles can be released at an open, wall or symmetry boundary by setting Release Particle to Yes.

Activates the release of particles or streaklines at a boundary. To activate the release of particles, select Yes under Release Particle drop-down list.

The following options gets activated, when you select Yes:

  • Release Frequency
  • Random Release
  • Radius of Particles
  • Initial Velocity
  • Release Position
Release Frequency

The particles can be released from a boundary to the flow just once or multiple times. This defines the release time of a particle patch and the time interval between two releases. In Simerics-MP, the particle release frequency is specified by one of the four options:

  • Once: Causes the release of particles one time, when a simulation is started from initial values or from a solution. Particles are not re-released for a continuation run.
  • time-step Interval: The particles are released in intervals in a transient simulation. With the release Frequency, , the particle release time interval would be -times the flow time-step: . For example, Frequency set to 3 would cause the release of particles at the beginning of the 1st, 4th, 7th, 10th, ... time steps.
  • Every time-step: The particles are released at the beginning of every time-step in a transient simulation
  • Time Interval: Particles are released at a fixed interval of time (in seconds). The input value of time-step controls the fixed interval of time. is directly specified.
  

Figure 5.230 - Release frequency

There are three options for tracing the direction of a particle released at a boundary, in case of a Massless particle:

  • Forward: Traces the motion of the particles forward in time.
  • Backward: Traces the motion of the particles backward in time, based on the current velocity field at each time-step. In that regard, it would be not being meaningful for an evolving flow field.
  • Both: Traces the motion of the particles both forward and backward in time.
  

Figure 5.231 - Release frequency (Once)
Random Release

For a flow boundary, the computational mesh divides it into a finite number of faces, corresponding to the boundary cells. When particles are released from the boundary into the flow domain, the boundary cells can be selected randomly for particle release, with a probability proportional to the area of cell faces. The Amount of Particles is determined using one of the two options:

  • Number: The total number of particles released is directly specified at a boundary under Number of Particles.
  

Figure 5.232 - Random release number
  • Mass Flux: The Mass Flux of the discrete particle phase is specified, and the number of the particles per parcel is calculated from the mass flux, radius and density.
 

Note: The setting of Amount of Particles option for Mass Flux is only active and displayed if the Particle Type is set to Has Mass under Particle module.
 

Figure 5.233 - Random release mass flux
Radius of Particles

The radius of particles is specified at the release time and remains unchanged, though for multiple releases, the radius of the particles can be different (specified using the Expression Editor as a function of time). In Simerics-MP, the shape of a particle is spherical, and its volume does not displace any fluid. For a particle Has mass, the radius (diameter) is used to compute the particle mass (volume) and fluid-particle drag force (relative Reynolds number), as shown in equation 5.10.1 and equation 5.10.1.

For a particle which is Massless, the Radius of Particles influences only the size of the particle. The Radius of Particles (see Figure 5.230) must have a value greater than zero.

 

Initial Velocity

For each particle, the initial velocity, is specified at the release position and the release time . The Massless particles have the same velocity as the local flow velocity, by default.

For Has mass particles, Simerics-MP allows the following velocity specifications.

  • Same as Fluid: The initial velocity is same as the local flow velocity, for the Has mass type of particles.

    • 5.564

    Note that can be flow velocity at the boundary face or/and boundary cell center where the particle is located at the time of release.

  

Figure 5.234 - Initial velocity (Same As fluid)

  • User Specified: Simerics-MP also allows a user-specified initial velocity:

    • 5.565

    where , and are the initial velocity components in a Cartesian coordinate system.

  

Figure 5.235 - Initial velocity (User Specified)
Release Position

For each particle, the starting/release position, , is specified at the release time . At a boundary, the release position can be determined by one of the three options:

  • Cell Center: The particles are released from the boundary cells: .
  • Face Center: The particles are released from the boundary faces:
  • Face and Cell Center: The particles are released from both the boundary cells and faces.

In the case of release from Face and Cell Center, the number of particles released from both the cell face and center are the same, which is either determined by the number of boundary faces/ cells or the total number of particles specified in Random Release. In other words, for Face and Cell Center, the total number of particles released is twice the specified Number of Particles or the number of boundary faces/cells.

It may be noted that if Random Release is set to No, Simerics-MP assumes that at every Face Center and/or Cell Center of the boundary, a particle is released.

  

Figure 5.236 - Release position

Interface Conditions

The interface attributes are the same as for the boundary conditions, if one side of the interface has been Blanked for Flow, i.e. it is a solid wall. If, the Flow module is Active on both sides of an interface, then the particle interface is treated as a default interface and cannot be assigned any special attributes.

 

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