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supersonic flow in compressor valve?

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Old   January 10, 2007, 11:50
Default supersonic flow in compressor valve?
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Perceptron
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Hello,

maybe you can help me with this problem: I'm simulating a compressor valve which is pressed onto its seat with a spring and opened by the increasing gas force from the upmoving piston. The CCL formulas used to describe the valve motion are nearly the same as in tutorial 20 (FSI-valve). Pressure and valve lift increase as the piston starts moving, but suddenly the following message appears:

ERROR #004100018 has occurred in subroutine FINMES. Message: Fatal overflow in linear solver.

When reviewing the results of the timesteps before, the subsonic flow (Ma=0,4) changes suddenly into supersonic (1,7) during the last step, which ends the solver. All input data seems physically correct, and analytic calculations of gas pressure and valve movement show good and reasonable results. The mesh also worked fine in simulations using little different values, for example for piston velocity. Thanks in advance for your support.

Perceptron
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Old   January 11, 2007, 18:02
Default Re: supersonic flow in compressor valve?
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Joe
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Reduce the timestep size during the sonic transition?
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Old   January 12, 2007, 01:16
Default Re: supersonic flow in compressor valve?
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Perceptron
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I already tried this. In some cases the solver error appeared earlier than with greater timesteps - a miracle. Perceptron
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