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Shock Induced Seperation

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Old   March 21, 2006, 13:34
Default Shock Induced Seperation
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Nick
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Has anybody had any experience with predicting shock induced seperation from a wall. We know that it is not happening in reality but our predictions do not tie up with this. We are using 2nd order descritization with standard K-e. We have tried various things mainly , changing the surrounding conditions but to no avail.

Cheers, Nick

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Old   March 21, 2006, 22:19
Default Re: Shock Induced Seperation
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Ahmed
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It is not clear to me what you really mean? Whether you are asking about a shock wave formed as a result of a separation Or separation results as a result of a shock wave. Both cases are physically possible provided the conditions are the proper ones. A separation bubble can cause a shock wave if the flow is supersonic. A shock wave is formed when a supersonic flow is deflected (perturbed) whether that perturbation is caused by a boundary layer, by a mechanical means,.........etc. Separation is caused by adverse pressure gradients. So what is your geometry and flow conditions, so one can try to engage in a useful discussion Good Luck
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Old   March 22, 2006, 05:16
Default Re: Shock Induced Seperation
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Nick
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Sorry for being vague, but I can't go into depth about the geometry. Its certainly a high mach number flow seperating as a result of the shock wave, (extremely unfaourable pressure gradient resulting in reverese flow within the boundary layer) Needless to say with a first order scheme it remains attached but switch on up to 2nd order and the flow jumps right off the surface. we're looking at a jet attached to a surface, with peak mach numbers of the order of 2.

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Old   March 22, 2006, 19:55
Default Re: Shock Induced Seperation
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Ahmed
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I normally start analysis using first order upwind schemes then I switch to second order (Just to save computing time), in simple language I never trust final results based on first order schemes, I do not know if that will help you. A jet attached to a surface, have you considered the so called The Coanda Effect? The Mach number reaching the value of 2, this might be the result of Thermodynamics, The speed of sound is a function of temperature, so check the thermodynamics of your problem. One more point:- For Your results based on first order schemes, Plot both the Entropy generation and the vorticity generation. Does the Entropy plot Satisfies the Second Law of Thermodynamics? Good Luck
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