Learning Forum

[Rui Qiao]

Hello CFX users,

I hope to perform a particle tracking study using CFX. My flow is steady and particle density is so low that there is only one-way coupling from flow to particle. Given this, I expected to finish the flow simulation and then perform particle tracking.

However, I heard that in CFX, flow simulations and particle tracking are done simultaneously. Is this right? This sounds quite counterintuitive.

Thanks!

Rui

[Mark Owens]

Particle tracking is not done simultaneously. The particle tracking is a separate algorithm to the flow solver and you can control how frequently it runs. Please see the CFX Solver Modelling Guide for Particle Transport Modelling->Particle Solver Control. If you expect the feedback to be weak you can do the particle update less frequently than the default.  But it may still be worth doing more than one particle update. It is probably better to let the solver discover that the feedback is weak and so it will automatically stop once both the flow and particle solvers have converged (and they will do that quite independently if there is no strong feedback) rather than trying to force the issue by running only the flow solver followed by a single instance of the particle solver, although you can do that if you want by adjusting the particle control parameters.

[nilotpalc]

 

 

Mark,

If I got this right, the particle solver control parameters you mentioned apply to a two-way coupled simulation. The first parameter on that list is “First Iter for Particle Calculation” and determines when the source terms from the solution of the fluid momentum equation will go into the particle momentum equation. After this, the source term going into the particle equation changes every iteration, representative of the effect of changing fluid calculations on the particles. This is reasonable for a two-way coupling. However, for a one-way coupling (which I explicitly specify in CFX), I’d rather want the source term going into the particle equation from the fluid calculation to not change with iterations. This is because I’d already have a converged fluid calculation, before introducing particles into the domain.

Is such a one-way coupling possible in CFX? If I could bypass the iterative calculations of the fluid momentum equation, that could save time.