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Old   July 16, 2003, 13:42
Default Supersonic flow over rough wall
Danny Tandra
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Dear All: Is there any special treatment if we are dealing with supersonic flow over a rough wall (In the contex of two equation model)?

The roughness height might go to the supersonic stream and create a shock.

As far as I know there is no paper that discuss this issue.

If I use rough wall function: U+ = (1/K)ln(Y/Ks) +8.5 where Ks is roughness height

Based on your intuation, do you expect a reasonable result or not (zero pressure gradient)

Thank's a lot

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Old   July 18, 2003, 05:35
Default Re: Supersonic flow over rough wall
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Which Reyblods number? Are you starting the domain with a developed velocity profile or a sharp leading edge (some viscous interaction effects may play soem role there and there is already a shock)?.

If your roughness height is smaller than the boundary layer thickness (which grows with M^2) I would not expect a new shock, the disturbances will not travel across the boundary layer but propagate downstream. The main differences could be in bypass transition an skin friction distributions.

However if your roughness is quite high, or is more like an obstacle, there would be local sepration of the boundary layer and secondary shock will appear.

This is my own opinion regarding laminar supersonic-hypersonic flow over a flat plate. In a two-equation model it seems to me that teh roughness will reduce/increase dissipation, however I cannot see straight away its influence over creating new shocks.

At the end everything will depend on Mach and Reynolds numbers

I do not if it helps but its my intuition only, maybe I am completly wrong ( I haven't read anything about it)

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