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Old   May 9, 2008, 18:36
Default negative density/pressure
  #1
littlelz
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I am calculating external air flow around airplane. I got the negative density/pressure error message as the Mach number=0.768. The calculation crashed. if I change the mach number to 0.125, the calculation can get through. what's the problem? which direction I should go? mesh? solver?

many thanks
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Old   May 10, 2008, 11:09
Default Re: negative density/pressure
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chw
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I think there is definitely something wrong with your solver code. Which method/scheme did you implement?
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Old   May 10, 2008, 16:07
Default Re: negative density/pressure
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littlelz
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actually, I don't know because I am using a research code. I don't know much on it. I do know it is using RANS method for turbulence modelling. are you sure there is nothing wrong on anything else. many thanks for your reply.

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Old   May 12, 2008, 03:07
Default Re: negative density/pressure
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Vinayender
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Hi,

Thats the sign of diverging. Better run with less CFL or change your grid (make it little more courser).

Thanks, Vinayender.
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Old   May 12, 2008, 17:24
Default Re: negative density/pressure
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littlelz
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thanks, Vinayender.

how less of the CFL is your recommendation?

do you think the mesh should be coarser, it seems there is shock for high mach number. am I supposed to refine the mesh? what's your point
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Old   May 13, 2008, 00:36
Default Re: negative density/pressure
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Vinayender
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Hi,

Who much CFL ??... that you can get by trial and error. If you dont want to change the coursen the grid then better use more dissipative schemes in your code.

One more sugesstion, better know about the code that you are using, that will help you out to figure whats the problem could be !!!!!

Thanks, Vinayender.
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