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Best CFX settings for supersonic free expansion [CFX] ? |
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August 30, 2012, 07:17 |
Best CFX settings for supersonic free expansion [CFX] ?
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ivan
Join Date: Jun 2012
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Hello there!
The objective of my simulation is to reproduce a free expansion in a vacuum vessel. The flow reaches, before 1s, supersonic velocity. I used adaptative timestep and I set the solver control as follows: TIME STEPS: First Update Time = 0.0 [s] Initial Timestep = 1e-06 [s] Option = Adaptive Timestep Update Frequency = 1 TIMESTEP ADAPTION: Courant Number = 5 Decreasing Relaxation Factor = 1 Increasing Relaxation Factor = 0.75 Maximum Timestep = 0.0001 [s] Minimum Timestep = 1e-06 [s] Option = RMS Courant Number SOLVER CONTROL: Turbulence Numerics = High Resolution ADVECTION SCHEME: Blend Factor = 0 Option = Specified Blend Factor END COMPRESSIBILITY CONTROL: High Speed Numerics = On END CONVERGENCE CONTROL: Maximum Number of Coefficient Loops = 20 Minimum Number of Coefficient Loops = 1 Timescale Control = Coefficient Loops END CONVERGENCE CRITERIA: Conservation Target = 1e-06 Residual Target = 1e-06 Residual Type = RMS END TRANSIENT SCHEME: Option = Second Order Backward Euler TIMESTEP INITIALISATION: Option = Automatic END END VELOCITY PRESSURE COUPLING: Rhie Chow Option = High Resolution END The simulation seems to be fine but after a certain time the residual begin to high. I don't undestand why there are this oscillations and why the convergerce criteria is not achieved. Is there any setting most suitable for my case? Why if I load another finer mesh residuals do not fall? |
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