33.3.29 Discrete Phase Model Dialog Box

The Discrete Phase Model dialog box allows you to set parameters related to the calculation of a discrete phase of particles. See Chapter  23 for details.

Controls

Interaction   contains parameters used for performing coupled calculations of the continuous and discrete phase flow. See Section  23.6.1 for details.

Interaction with Continuous Phase   enables a coupled calculation of the discrete phase and the continuous phase.

Update DPM Sources Every Flow Iteration   enables calculation of particle source terms at every DPM Iteration. It is recommended for unsteady simulations.

Number of Continuous Phase Iterations per DPM Iteration   allows you to control the frequency at which the particles are tracked and the DPM sources are updated.

Particle Treatment   contains options for choosing to treat the particles in an unsteady or a steady fashion.

Unsteady Particle Tracking   enables unsteady tracking of particles.

Track with Fluid Flow Time Step   enables the use of fluid flow time steps to inject the particles.

Inject Particles at   contains parameters to decide when to inject the particles for a new time step.

Particle Time Step   enables injection of particles for every particle time step.

Fluid Flow Time Step   enables injection of particles for every fluid flow time step. In any case, the particles will always be tracked in such a way that they coincide with the flow time of the continuous flow solver.

Particle Time Step Size   specifies particle time step size for the calculation.

Number of Time Steps   allows you to specify the number of time steps for the calculation.

Clear Particles   clears the particles that are currently in the domain.

Tracking   contains two parameters to control the time integration of the particle trajectory equations.

Tracking Parameters   contains parameters that control the tracking of particle trajectories. One simple rule of thumb to follow when setting the two parameters below is that if you want the particles to advance through a domain of length $D$, the Length Scale times the number of Max. Number of Steps should be approximately equal to $D$. See this section in the separate Theory Guide for details about the items below.

Max. Number of Steps   is the maximum number of time steps used to compute a single particle trajectory via integration of this equation in the separate Theory Guide and  this equation .

Specify Length Scale   when enabled allows you to specify the length scale.

Length Scale   controls the integration time step size used to integrate the equations of motion for the particle. It appears only when the Specify Length Scale option is enabled.

Step Length Factor   specifies the value of $\lambda$ in Equation  23.2-2.

Drag Parameters   allows the setting of the drag law used in calculating the force balance on the particles. See this section in the separate Theory Guide for details on the items below.

Drag Law   is a drop-down list containing three choices:

spherical   assumes that the particles are smooth spheres.

nonspherical   assumes that the particles are not spheres, but are all identically shaped. The shape is specified by the Shape Factor.

Stokes-Cunningham   is for use with sub-micron particles. A Cunningham Correction is added to Stokes' drag law to determine the drag.

high-Mach-number   is similar to the spherical law with corrections to account for a particle Mach number greater than 0.4 or a particle Reynolds number greater than 20.

dynamic-drag   accounts for the effects of droplet distortion. This drag law is available only when one of the droplet breakup models is used in conjunction with unsteady tracking. See this section in the separate Theory Guide for details.

Shape Factor   specifies the shape of the particles when nonspherical is selected as the Drag Law ( $\phi$ in this equation in the separate Theory Guide). It is the ratio of the surface area of a sphere having the same volume as the particle to the actual surface area of the particle. The shape factor value cannot be greater than 1.

Cunningham Correction   ( $C_c$ in this equation in the separate Theory Guide) is used with Stokes' drag law to determine the force acting on the particles when the particles are sub-micron size. It appears when Stokes-Cunningham is selected as the Drag Law.

Physical Models   contains optional discrete phase models and their relevant parameters.

Options   contains additional models that can be included in the calculation. See Section  23.2.5 for more information.

Particle Radiation Interaction   includes the effect of radiation heat transfer to the particles ( this equation in the separate Theory Guide). You will also need to define additional properties for the particle materials (emissivity and scattering factor), as described in Section  23.5.2.

This item appears only if the P-1 or discrete ordinates model is selected in the Radiation Model dialog box.

Thermophoretic Force   enables the inclusion of a thermophoretic force on the particles as an additional force term. See this section in the separate Theory Guide for details.

Brownian Motion   enables the incorporation of the effects of Brownian motion. See this section in the separate Theory Guide for details.

Saffman Lift Force   enables the inclusion of Saffman's lift force (lift due to shear) as an additional force term. See this section in the separate Theory Guide for details.

Erosion/Accretion   enables the monitoring of erosion/accretion rates at wall boundaries. See Section  23.2.5 for details. This item appears only if Interaction with Continuous Phase is enabled.

Two-Way Turbulence Coupling   enables the effect of change in turbulent quantities due to particle damping and turbulence eddies.

Spray Model   contains parameters that control droplet breakup and collision. (This section of the dialog box appears only if Unsteady Tracking is enabled.)

Droplet Collision   includes the effect of droplet collisions. See this section in the separate Theory Guide for details.

Droplet Breakup   includes the effects of droplet breakup.

Breakup Model   contains parameters that control droplet breakup. (This item appears only if Droplet Breakup is enabled.)

TAB   enables the Taylor Analogy Breakup (TAB) model, which is applicable to many engineering sprays. This method is based upon Taylor's analogy between an oscillating and distorting droplet and a spring mass system. See this section in the separate Theory Guide for details.

Wave   enables the wave breakup model, which considers the breakup of the injected liquid to be induced by the relative velocity between the gas and liquid phases. See this section for details.

Breakup Constants   contains model constants used in the equations for spray breakup. (This item appears only if Droplet Breakup is enabled.)

y0   (only for the TAB model) is the constant $y_0$ in this equation in the separate Theory Guide.

Breakup Parcels   is the number of child parcels the droplet is split into, as described in this section in the separate Theory Guide.

B0   (only for the wave model) is the constant $B_0$ in this equation in the separate Theory Guide.

B1   (only for the wave model) is the constant $B_1$ in this equation in the separate Theory Guide.

UDF   contains parameters that can be used to customize the discrete phase model using UDF. See the separate UDF Manual for details about user-defined functions.

User-Defined Functions   lists will show available user-defined functions that can be selected to customize the discrete phase model.

Body Force   contains a drop-down list of user-defined functions available for including additional body forces.

Erosion/Accretion   contains a drop-down list of user-defined functions available for incorporating non-standard erosion rate definitions. This item will appear only when the Erosion/Accretion option has been enabled.

Scalar Update   contains a drop-down list of user-defined functions available for calculating or integrating scalar values along the particle trajectory.

Source   contains a drop-down list of user-defined functions available for modifying interphase exchange terms.

Spray Collide Function   contains a drop-down list of user-defined functions available for modifying spray collide function.

DPM Timestep   contains a drop-down list of user-defined functions available for modifying DPM time step.

User Variables   lists the user input variables.

Number of Scalars   sets the number of scalar values used in the calculations with user-defined functions.

Numerics   tab gives you control over the numerical schemes for particle tracking as well as solutions of heat and mass equations. See Section  23.2.8 for details.

Options   contains parameters of solutions of heat and mass equations.

Accuracy Control   enables the solution of equations of motion within a specified tolerance.

Tolerance   is the maximum relative error which has to be achieved by the tracking procedure.

Max. Refinements   is the maximum number of step size refinements in one single integration step. If this number is exceeded the integration will be conducted with the last refined integration step size.

Coupled Heat-Mass Solution   enables the solution of the particle heat and mass equations using a stiff, coupled ODE solver with error tolerance control. See Section  23.2.8 for details.

Track in Absolute Frame   enables tracking the particles in the absolute reference frame.

Tracking Scheme Selection   contains parameters for selection of numerical schemes.

Automated   enables a mechanism to switch in an automated fashion between numerically stable lower order schemes and higher order schemes, which are stable only in a limited range.

High Order Scheme   can be chosen from the group consisting of trapezoidal and runge-kutta scheme.

Low Order Scheme   consists of implicit and the exponential analytic integration scheme.

Tracking Scheme   allows to choose any of the tracking schemes. You also can combine each of the tracking schemes with Accuracy Control. It is selectable only if Automated is switched off.

Parallel   contains parameters that control the compute nodes for performing discrete phase calculations in parallel. See Section  23.8 for details.

Message Passing   enables cluster computing and also works on shared memory machines. With this option, the compute node processes themselves perform the particle work on their local partitions and particle migration to other compute nodes is implemented using message passing primitives. No special requirements are placed on the host machine. Note that this model is not available if the Cloud Model option is turned on under the Turbulent Dispersion tab of the Set Injection Properties dialog box. The Message Passing option is irrelevant for the serial ANSYS FLUENT code while the Shared Memory option remains valid.

Shared Memory   allows you to specify parameters for performing the calculations on shared-memory multiprocessor machine.

Workpile Algorithm   specifies that the discrete phase calculations are to be performed on a shared-memory multiprocessor machine.

Number of Threads   specifies the number of threads to be used in performing the particle calculations. By default, this parameter is equal to the number of compute nodes you specified for the parallel solver. (This item appears only if Workpile Algorithm is enabled.)