Hi
This is Ravi. i am trying to create a separation bubble on a flat plate using a contoured upper wall. I want to apply same pressure distribution of a given blade on the flat plate. I have read few paper and they mentioned something like this:
" The shape of the contoured wall is designed using a simple one-dimensional continuity argument to match the pressure distribution measured on the flat plate to that measured on the T106 LP turbine cascade."
It would be helpful if some one tell me the procedure or related derivation.
The simple schematic of the contour wall is attached
I am not sure if you can make it using commercial CFD codes, because you are going to depict a 3D phenomenon in a 2D screen plane.
Dear Ravi,
if you prescribe some pressure distribution, you can rearrange the Bernoulli and the continuity equation in that way to determine the cross section as a result. The cross section represents the passage height between the flat plate and the opposite wall, providing the opposite wall geometry. Depending on the Mach number, you can use incompressible or compressible Bernoulli equation. The figure you show looks like the experimental setup from TU Berlin (Hourmouziadis, Lou, Talan). A similar test case has been used at Univ. Genova:
-Simoni D, Ubaldi M, Zunino P, Lengani D, Bertini F (2012) An experimental investigation of the separated-fow transition under high-lift turbine blade pressure gradients. Flow Turbul Combust 88:45–62
-Matteo Dellacasagrande et al: Response of a fat plate laminar separation bubble to Reynolds number, free‑stream turbulence and adverse pressure gradient variation, Experiments in Fluids (2020) 61:128
However, the wall geometry from this 1D theory will probably not provide a good agreement to the prescribed pressure distribution, since the passage is 2D and asymmetric. Further, some experimentalists report about separations at the opposite wall, considerably retarding the flow. Hence, I highly recomment to mesh the complete test case, including also the passage below the flat plate, and to run several CFD iterations for fine-tuning the wall geometry. Of course, you can use the 1D geometry as initial step. Don't forget to use elliptic leading edge. Also, you should use flexible materials for the wall construction.
Best regards,
Dragan
Thanks Dragon
I did the same using a turbine blade and I found that a separation bubble is also forming on the contour wall. How to remove it. I cannot change the countour shape.
Do i need to apply suction at upper wall? or i need to decrease the velocity.
Reducing the velocity will reduce the adverse pressiert gradient and the separation will disappear at some point. However, this will also change the Reynolds number, hence I think this is a bad procedure. Active flow control is very powerful but also non-practical. I suggest some passive measure, e.g splitter vane or trip wire prior to the separation.
Best regards
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