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Negative densities at the start of a run

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Old   February 21, 2003, 10:09
Default Negative densities at the start of a run
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I am trying to model the supersonic flow between two finite width wedges. The model has approx 250000 elements. I am attempting to run it as an inviscid calculation with an upwind scheme. The solver fails within the first three steps citing 'negative densities found in more than 100 cells as the error'. how can this be rectified, any help in this matter is greatly appreciated.

cheers nandu
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Old   February 21, 2003, 12:17
Default Re: Negative densities at the start of a run
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Try pseudo-transient runs. Adjust time step to taste. Also, try using double-precision. Worked for me.
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Old   April 20, 2003, 23:48
Default Re: Negative densities at the start of a run
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Same problem... for my transient moving mesh case. I've tried: 1) changing the time step to be one order to order of magnitude smaller but didn't work. 2) using double precision but didn't work 3) changing all relaxation factors (everything not just pressure) but didn't work 4) all above with 2-3 different values as trial and error and still didn't work. 5) looking into mesh quality possibilities now... don't know yet.

Appreciate if someone with experience could give some tips here. Thanks.
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Old   May 13, 2003, 17:18
Default Re: Negative densities at the start of a run
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I've had this problem quite often. From my expirence (I'm a fairly new user) mesh quality is the cause. I've only come across this when using PROAM to mesh.

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