POLYFLOW - non-conformal interface for internal flow simulation yields strange temperature results
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A non-isothermal flow simulation involving non-conformal interface and (discontinuous) temperature imposed along outside walls may produce unrealistic (unphysical) temperature distribution, while the flow seems properly calculated. In fact, the temperature at the non-conformal interface exhibits overshoots and undershoots. Changing the dilation coefficient or the volume coefficient for non-conformal boundary donditions does not help. We suspect that there is a conflict of boundary condiitons. Indeed, the set of constraints created at the non-conformal interface may be affected by the additional temperature condition imposed; this may become worse when there is a discontinuity in temperature boundary conditions on both sides of the non-conformal interface. The case is presumably overconstrained. Actually, a discontinuity in temperature boundary conditions may cause troubles for the set of constraints between variables, and this adds to the fact that discontinuity in temperature boundary conditions usually produce oscillations, which are also propagated with the flow. In order to circumvent this, temperature boundary conditions along walls can be replaced by forced convection condition alpha*(T-Talpha), where a reasonnable value for alpha could be 250 W/m/°C while Talpha corresponds to the initially imposed temperature. For a heat conduction calculation, this has produced a significantly better temperature distribution. |
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