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22.11.5 Physical Models for the Discrete Phase Model

This section provides instructions for using the optional discrete phase models available in FLUENT. All of them can be turned on in the Discrete Phase Model panel (Figure  22.11.3).

Define $\rightarrow$ Models $\rightarrow$ Discrete Phase...

Figure 22.11.3: The Discrete Phase Model Panel and the Physical Models
figure



Including Radiation Heat Transfer Effects on the Particles


If you want to include the effect of radiation heat transfer to the particles (Equation  13.3-13), you must turn on the Particle Radiation Interaction option under the Physical Models tab, in the Discrete Phase Model panel (Figure  22.11.3). You will also need to define additional properties for the particle materials (emissivity and scattering factor), as described in Section  22.14.2. This option is available only when the P-1 or discrete ordinates radiation model is used.



Including Thermophoretic Force Effects on the Particles


If you want to include the effect of the thermophoretic force on the particle trajectories (Equation  22.2-14), turn on the Thermophoretic Force option under the Physical Models tab, in the Discrete Phase Model panel. You will also need to define the thermophoretic coefficient for the particle material, as described in Section  22.14.2.



Including Brownian Motion Effects on the Particles


For sub-micron particles in laminar flow, you may want to include the effects of Brownian motion (described in Section  22.2.1) on the particle trajectories. To do so, turn on the Brownian Motion option under the Physical Models tab. When Brownian motion effects are included, it is recommended that you also select the Stokes-Cunningham drag law in the Drag Law drop-down list under Drag Parameters, and specify the Cunningham Correction ( $C_c$ in Equation  22.2-11).



Including Saffman Lift Force Effects on the Particles


For sub-micron particles, you can also model the lift due to shear (the Saffman lift force, described in Section  22.2.1) in the particle trajectory. To do this, turn on the Saffman Lift Force option under the Physical Models tab, in the Discrete Phase Model panel.



Monitoring Erosion/Accretion of Particles at Walls


Particle erosion and accretion rates can be monitored at wall boundaries. These rate calculations can be enabled in the Discrete Phase Model panel when the discrete phase is coupled with the continuous phase (i.e., when Interaction with Continuous Phase is selected). Turning on the Erosion/Accretion option will cause the erosion and accretion rates to be calculated at wall boundary faces when particle tracks are updated. You will also need to set the Impact Angle Function ( $f(\alpha)$ in Equation  22.5-1), Diameter Function ( $C(d_p)$ in Equation  22.5-1), and Velocity Exponent Function ( $b(v)$ in Equation  22.5-1) in the Wall boundary conditions panel for each wall zone (as described in Section  22.13.1).



Including the Effect of Particles on Turbulent Quantities


Particles can damp or produce turbulent eddies ([ 269]. In FLUENT, the work done by the turbulent eddies on the particles is subtracted from the turbulent kinetic energy using the formulation described in [ 100] and [ 9].

If you want to consider these effects in the chosen turbulence model, you can turn this on using Two-Way Turbulence Coupling, under the Physical Models tab.



Tracking in a Reference Frame


Particle tracking is related to a coordinate system. With Track in Absolute Frame enabled, you can choose to track the particles in the absolute reference frame. All particle coordinates and velocities are then computed in this frame. The forces due to friction with the continuous phase are transformed to this frame automatically.

In rotating flows it might be appropriate for numerical reasons to track the particles in the relative reference frame. If several reference frames exist in one simulation, then the particle velocities are transformed to each reference frame when they enter the fluid zone associated with this reference frame.


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