two-way coupling problem in multiphase simulation
 

Hi all,

I am working on the simualtion of spray. The breakup models I used are LISA and TAB. I am using k-Epsilon model for turbulence, two-way coupling and schiller Naumann for drag force model. Turbulent dispersion force is on with default Eddy viscosity ratio limit.
The setting seems alright. However, there is huge difference between the spray droplet speed and the flow field's speed (Max. speed are 24ms^-1 and 0.27ms^-1 respectively). Is there anything I can do for improving the two phase coupling performance?

Thanks!

I suggest you check the droplet diameter and other parameters pertinent.
What you have set as you said is not the matter, you needn't rework them.
Look into the help docs carefully.

Hi Jeff,

I think, you need to check your physics of the problem first, What is an approximate size of your particles and the particle loading ( no of particles/ m3 of Air). If particles are too big and if you think that they can change the momentum of the air, then only use two way coupling other wise one way coupling is good. Please check how you have defined the density of the spray particles?

Thanks! I will check that

Hello everyone,


I am using CFX transient lagrangian particle tracking model to track particles and determine their concentration in a clean room.
The particle volume fraction is very low (< 10^-8). I am using full buoyancy model. The particles are to be simulated for different particle temperature and hence varying buoyancy.

The particles size ranges from 0.5 micron to 5 micron.


Do i need to use two way coupling or is one way coupling sufficient?.


Thank you all.
Ganesh

You should decide on the coupling by the significance of the effect of one phase on the other. The particles are affected by the air flow, of course - that is why you are using a particle tracking model. But it would be very unusual if such small and sparse particles then had a significant effect on the air flow.

In that case you can model this as one-way coupling.

But I am just guessing as I do not know what you are doing, why you are doing it and what physics is important. You have to make your own decision.

Hello Glenn,
Thank you for the reply. I am trying to simuate the effect of particle temperature on the buoyancy.The particles are generated by an injecion molding machine in a cleanroom. I would like to check how the temperature effect the trajectory and hence concentration of particles in the clean room.


Thank you,
Ganesh

Does the temperature make the air have buoyant effects? Then the moving air would affect the particles?

Or are you saying the temperature of the particles affects the buoyancy? This sounds highly unlikely as the particles (if they are some sort of solid or polymer) are going to have a density far larger than the surrounding air, so a small change in the density of the solid due to temperature is going to have no significant effect.

Hello Glenn
Thank you for the reply.
Yes the temperature makes the air have buoyant effect. The material is polypropylene particles. I have used full buoyancy model with ideal gas as continuous fluid . And thermal energy as heat transfer for air and particle temperature for particles.


Thank you,
Ganesh Naik

In that case it sounds like this case is two way coupling as the particles affect the air flow. In this case the coupling is indirect as it is through heat transfer, but it is indeed coupled. So you need a two way coupled model.

Have you considered doing this with a Eularian particle model? It may well be easier and will probably be much faster and easier to get to a mesh independent solution.

Hello Glenn,
Thank you for the reply. I have not tried it using Eularian Model. I will read about it.


Thank you,
Ganesh