# Boundary condition question, help please!

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 June 10, 2009, 15:30 Boundary condition question, help please! #1 New Member   Francisca Join Date: Jun 2009 Posts: 14 Rep Power: 16 Hello again. I posted recently about a multiphase problem. The idea is to model a launder with a flow of water that carries particles, and above this is air. I first did the case of water and air (free surface), and to express the inlet condition I had to use a step to say that the phases where separated. This is, in the volume fraction of Air at the inlet I put the expression UpVFAir=step((z-w[m])/1[m]) ,where w is the water height, and for the water volume fraction I put 1-UpVFAir. Now that I want to include the particles, which I described as a liquid dispersed phase, I don't know how to include them so that they remain only in the water area. I know the air inlet volume fraction will remain the same, but how should I put the water and particles? I know the volume fraction of each, but I don't know how to put it so that they don't mix with the air. Thank you all Francisca

 June 10, 2009, 18:03 #2 Senior Member     George Join Date: Mar 2009 Location: Birmingham, UK Posts: 257 Rep Power: 18 you need to initialize the air,water and particle volume fraction. create an expression for water as you did in your example and multiply the equation with a dispersion factor for the sake of this example vfwater * 0.9 . in a similar way express the same equation for the volume fraction of the particles in this case vfwater * 0.1 . until now particles and water share the same volume in your domain. for the air you need to leave the initialization on automatic and cfx will set the rest of your fluid in the remaining volume in your domain dont forget to enable buoyancy __________________ Top 4 tips 1. Knowledge is everything and Ignorance is dangerous. 2. Understand your limitations and try to eliminate them. 3. Get yerself a bike and hoon the chuffer. You will soon learn why dogs like to hang their heads out the car window. 4. Please before asking any questions on how to run simulations in CFX, go though all the tutorials

 June 11, 2009, 12:52 Thanks!! #3 New Member   Francisca Join Date: Jun 2009 Posts: 14 Rep Power: 16 Thank you!!

 Tags ansys, boundary condition, cfx, cfx11, multiphase