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Translational periodicity with specified mass flow rate

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Old   August 12, 2014, 01:48
Default Translational periodicity with specified mass flow rate
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Kalle Tiitinen
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Fellow CFX users,
I wanted to simulate a fully developed pipe flow using the translational periodicity bc with user specified mass flow rate. My geometry is a 90 degree section (taking advantage of the rotational periodic geometry) 4 diameters long. Fluid is water. As basic as a simulation can get.

When I apply translational periodicity with specified mass flow rate it appears impossible to obtain convergence as the solution starts to oscillate (pressure loss of the pipe section going up and down). This happens with different Reynolds numbers alike. Adjusting the pressure update multiplier even to small values like 0.001 cannot stabilize the solution. When I change interface model to specified pressure change the solution converges monotoniously and is completetely stable (resulting in same Re as targeted with specified mass flow rate).

Has anyone had similar experience with convergence using the specified flow rate? I am really not confident trying to use it for any real case if even this dummy pipe cannot be properly solved. Any ideas if I should check some particular settings?
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cfx 14.5, convergence problem, translational periodicity

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