I need a periodic BC where mass flow rate is specified to model fully developed flow, and another periodic BC with no pressure drop. However, once I define the mass flow rate for one periodic BC, another periodic BC is defined with the same value. Can anyone help to solve this issue?
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Yes, probably this is an issue in Fluent when the mass flow rate is specified instead of the pressure gradient. I never worked with double periodicity and the mass flow rate but, if you have experienced troubles, there is probably no solution except reverting to the pressure gradient.
Paolo Lampitella Thank you for the suggestions. I have made double periodic conditions (both streamwise and spanwise direction) for a simple rectangle channel flow. The flow is in x-direction (streamwise). Previously, the calculation of the volume flux using Q=2/3*Vcentreline*Across-area would give the mass flow inlet by multiplying with fluid density. I suspect that the calculation of the cross sectional area in the equation above (in x direction only) differs from the calculation from FLUENT since we have two translational plane (x&z direction) right now. I suggest that the mass flow rate that is applied in fluent to consider the total cross sectional area of two planes (A in x-direction and A in z-direction). Then, we can see that the computed velocity in initialization is tallied with the Reynolds number and flows only in one direction (x-direction). Any comment on my suggestion?
Have you tried first a 2d channel with a single periodic direction and mass flow rate prescribed?
Filippo Maria Denaro No i haven’t. I will give a try on that later. Thank you.
That's probably the case, but you can't compute the mass flow rate in that way for a turbulent flow. That formula is valid for laminar cases.
Try using a pressure gradient in x direction only
Paolo Lampitella I see. Thanks for the info! I will give a try.
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