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Problem with Negative Sonic Velocity.....

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Old   September 25, 2005, 15:13
Default Problem with Negative Sonic Velocity.....
Mohamed Yousuf
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Presently i am doing a code development for Viscous compressible flow through cascades.. For code validation part, i took viscous flow over NACA0012 aerofoil problem. Forthat, i created a square domain around the airfoil and discretized using Gambit (unstructured grid). Boundary conditions are top and bottom walls of square i applied zero gradient BC.. For left wall i applied Farfield BC For Right wall i applied outlut extrapolation BC and for airfoil i applied No-slip Bc My problem is... While running my code... after 10- 100 later... i am getting negative sonic velocity and negative pressure nearby trailing edge of airfoil... where i am doing mistake ?? will Domain Section and length affect the solution? thanks...

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Old   September 25, 2005, 16:47
Default Re: Problem with Negative Sonic Velocity.....
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1- Top and bottom BC are the same as the inlet BC i.e. far field 2- Negative pressure etc, Assuming your code is free of bugs, normally this needs reducing the underrelaxlation parameters, this is a sign of a numerical instability 3- domain should extend at least 10 Chord length in all directions 4- Since you are using Gambit, you have access to FLUENT web site, check their tutorial library,
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