# Compressible Fluid in COMET

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 February 15, 2005, 19:58 Compressible Fluid in COMET #1 saang Guest   Posts: n/a I have tried to implement compressible fluid with free surface flow by defining "density in user subroutine" for specie 1. Actually, it likes there are 2 materials in one domain (Domain Mat is air (constant density)and Specie 1 is water (compressible density)). But the solution is blown up. Does anyone face this problem before and how you guys tackle it? By the way, i am doing fine to solve compressible fluid in the regular domain (one material in one domain)

 February 18, 2005, 07:57 Re: Compressible Fluid in COMET #2 JBS Guest   Posts: n/a If have the same problem with cavitation. The pressure denpendent density description for the liquid works fine as long as I do not activate cavitation. But when activating the cavitation I get NaN for the produced species in the first Iteration (although there is no cavitation at the beginning of the simulation at all). I have a support case on that, I'll report when I have news on that.

 February 18, 2005, 18:50 Re: Compressible Fluid in COMET #3 saang Guest   Posts: n/a I didnt activate any cavitation. I just use "Free Surface with HIRC". I got the same result as yours that NaN error occur at SP1 at very first iteration of the first time step. Please let me know if you have any further information. It would be great if you could email me directly. Thank you in advance.

 February 22, 2005, 11:19 Re: Compressible Fluid in COMET #4 4xF Guest   Posts: n/a You can't run compressible VOF using the COMET solver. This is inherent to the design of the solving algorithm itself when the free-surface modeling with HRIC is used. The formulation is based on the assumption that the fluids (liquid & gas) are inmiscible and the flow is incompressible (since div(V)=0 is assumed for the free-surface modeling).

 February 22, 2005, 12:47 Re: Compressible Fluid in COMET #5 JBS Guest   Posts: n/a I don't use HRIC for cavitating flows.

 February 22, 2005, 22:16 Re: Compressible Fluid in COMET #6 saang Guest   Posts: n/a To Mr 4xF, Thank you so much for your help. It's very helpful informatin. By the way, my model is about to squeeze the volume to gain the pressure (due to bulk modulus of water) and, then track the free surface. Is it possible to implement compressible fluid at the first few time steps without "free surface", and then, in the later time step after I got the pressure, I turn "compressible fluid" off and turn on HIRC for free surface?

 March 5, 2005, 03:18 Re: Compressible Fluid in COMET #7 xhliu1 Guest   Posts: n/a I have the same problem with JBS,If some one can help us to solve it!!

 March 5, 2005, 03:24 Re: Compressible Fluid in COMET #8 xhliu1 Guest   Posts: n/a Hello,everyone! I want to change the solving algorithm in star-cd,is it possible?

 March 5, 2005, 22:36 Re: Compressible Fluid in COMET #9 xhliu1 Guest   Posts: n/a I have a problem with cavitation. The pressure dependent density description for the liquid works fine as long as I do not activate cavitation. But when activating the cavitation I get NaN for the produced species in the first Iteration (although there is no cavitation at the beginning of the simulation at all). As I using the cavitation model,density of the heavy fluid just can be set as a constant number.Can I using some method to solve this problem?

 March 19, 2005, 22:45 Re: Compressible Fluid in COMET #10 Tridib Guest   Posts: n/a Hallo everybody, I have COMET software(education version). I need the full user manual. Please help me in getting a comet user manual. Tridib

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