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Old   December 18, 2005, 18:39
Marco Giuliani
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Dear Fluent users ,

I deal with a compressible nozzle; i know only total pressure and total temperature at the inlet , and static pressure at the outlet. Which value i must input for the supersonic/initial gauge pressure? It seems to me that supesonic/initial gauge pressure should be the static pressure at the inlet , so i tried to verify this calculating this value for the nozzle cases in fluent tutorial , making the hypothesis of isentropic evolution of flow , but the values don't match. Can someone help me to understand the exact meaning of "supesonic/initial gauge pressure" and suggest if an isentropic treatment to get it is correct? Is supesonic/initial gauge pressure really important and must be chosen carefully or it is used only to initialize the solution so one can approximate it?

Thanks in advance

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Old   December 19, 2005, 02:24
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Initializing solution closer to final values will, of course, shorten the calculation time. But, in this particular case (compressible nozzles) it will make no difference, because it is almost impossible to correctly initialize the solution in the whole flow domain, even when using patching! So, simply impose an equal or a bit lower value for this initial/supersonic pressure (which after all is the static pressure for the inlet area) compared to the total pressure. And that's it.

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