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Expansion of a pressurized channel with negligible initial velocity
Posted Jun 14, 2012, 8:31 p.m. EDT Acoustics & Vibrations, Computational Fluid Dynamics (CFD) Version 4.2 0 Replies
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I have a case in which a gas, contained in a chamber, with initial uniform density, has a pressure distribution highly non-uniform (6 times the average pressure at maximum), which consists of a channel, with diameter 4 times smaller than the caracteristic length of the chamber, with something like p0*(1+6*exp(-x^2-y^2)) pressure initial value. Actually you get such a case when a very fast and violent plasma discharge just passed in an energetic streamer, and heated the gas faster than it could expand. The Temperature rises but the density moves only afterwards; and the pressure profile has no discontinuity at the beginning, because the plasma boundary is "smooth" (discontinuities come later in the process, of course).
But when I try using the High Mach Number flow module (hmnf) in 3D, it gives me first "attempt to evaluate negative power of zero" all the time, and it does this even when I try to make non-zero all initial values, I only have air, I specified everything correctly I thought...but still I have this "negative power of zero" problem...it only goes away when I put an "artificial" inlet and outlet, but then it would keep saying me "stiffness matrix with NaN/inf" numbers. One problem instead of another; actually I do not know if it would still tell me about the negative power of zero problem, once the stiffness matrix becomes acceptable again! It may be a pile of problems...the "zero" problem is especially irritating because all the log shows is the sign "^", saying that the problem occured when performing the operation "^". Yes, but WHERE!...
So I would like to know if someone knows of a model of acoustics, where the pressure perturbation is no longer a perturbation and exceeds by 6 or 7 times the "reference pressure" of the gas itself. Maybe the high mach number flow module is not made for that, too complicated or something else...there are few models using this high mach number flow module, I found this sajben diffuser model but it is a stationary case, I need something time dependent...
Does anyone has any references or user experience about that kind of problem?
Hello Jean-Pierre Matan
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