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Old   January 29, 2004, 13:31
Default Compressible Flow Problems
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Gopher
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I'm doing a final year project of a simulation of the flowfield around what is essentially a missile nosecone travelling at Mach 2. At the moment, I'm trying to work up a grid so that I can do a series of runs to get results out of, however I've encountered a number of problems. The first one has been partially resolved (something to do with a certain amount of cells being too much for the VR-Results viewer to handle?) however the second one is a bit of a showstopper, and goes something like this:

absolute pressure .le. 0. run aborted l0p =15371536 i = 396 p =-1.113567E+05 press0 = 1.000000E+05

namsub= PRFILE; namfun= G 9S14 set varmin(p1)) to: - 0.5*PRESS0, say, for a near-atmospheric-pressure flow isweep = 30 izstep = 44 ixy slab= 396

I tried setting the Min P1 value to half PRESS0, however at the point where the pressure singularity occurs, the results suddenly go crazy, so this isn't the ideal solution.

I've already read elsewhere on this board that this error is indicative of a problem elsewhere like in boundary conditions or something, however my limited experience in CFD in general pretty much precludes me from knowing what I should be doing, what to look for and what "looks right".

I don't suppose anyone can give me some ideas, in more Layman terms? Any help would be appreciated.
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Old   February 2, 2004, 01:44
Default Re: Compressible Flow Problems
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Leon Mills
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Gopher,

I have had the same problem. For me it is generally related to a convergence problem.

I typically adjust the relaxation parameters, so that they are less tight. For me the big ones are density, and pressure then velocity.

Hopes this helps.

Leon

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