Fluids

Fluids

Wrong total pressure for thermally perfect gas

    • shuvCFD
      Subscriber
      Hello everyone. nThere seems to be a critical error produced by Ansys Fluent and I would appreciate any comments in this regard. We are trying to simulate a compressible inviscid, thermally perfect gas in the ANSYS Fluent 19.1. i.e. the Cp is a function of temperature. The Cp is modelled as piecewise polynomial. The geometry is simply a hypersonic inlet and the inlet of the geometry is modelled as pressure-far-field. The incoming flow is hypersonic.The problem is with the estimates obtained for total pressure everywhere in the domain (over-prediction), including the freestream! A quick check from the simple gas dynamic relations for the freestream reveals a completely different value as compared to the estimates obtained from Fluent (since it is freestream with temperature ~230K, it is expected the Cp or gamma, won't be too different than 1.4, for diatomic air. Hence the gas dynamic relations in the inlet should hold). Moreover, changing the Cp treatment from piecewise polynomial to kinetic theory, the Cp values were now severely under-predicted.Upon treating the gas as calorically perfect gas (i.e. Cp constant), the total pressure values were found to be correct and equal to the ones obtained from isentropic relations. I wonder if anyone has faced such issues and if the total pressure values can be trusted at all. nRegardsn
    • Rob
      Ansys Employee
      I'm not aware of any issues, can you check for convergence and post some images?n
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