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CFX predicts soundwaves at the wrong frequency.

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Old   July 28, 2016, 15:38
Default CFX predicts soundwaves at the wrong frequency.
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Michael P. Owen
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Good afternoon, gents. I have a strange on I am scratching my head over.

I have a transient rotating machine problem with a blade passing frequency of 3050 Hz. I'm running the model with 32 timesteps per blade passing and 20 elements per wavelength, which should be adequate to to resolve the acoustic waves. Ideal gas, total energy equation on. Convergence criteria is 10^-5 RMS. Imbalances are running 0.01%. Acoustic nonreflectivity on the boundaries. Everything appears well resolved and well converged. However, the traveling acoustic waves have a frequency much lower than expected, around 2000 Hz. Is there something obvious that I'm missing here? Is 20 elements per wavelength not adequate for acoustic wave propagation in CFX?



Nevermind. User error. Frame Change model left as Frozen Rotor instead of Transient Rotor/Stator. Derp.
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