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problem is modeling and simulation of an air foil

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Old   November 29, 2010, 04:41
Default problem is modeling and simulation of an air foil
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hellow,

i have to simulate one system which is the flow of air around an air foil. the speed from the inlet - the circle red - is around 160 m/s. the outlet is marked with the green circle. this image shows the model of the problem:
1.jpg

the following picture shows the mesh;
2.jpg

the problem is the pressure distribution i'm getting which is totally wrong. what i can do now ?
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Old   November 29, 2010, 18:24
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Glenn Horrocks
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Why do you say the pressure distribution is totally wrong? What are you comparing it against? If you are comparing it against far-field values (ie in an infinite domain) then of course your result will be totally different as you have a very constrained flow with a upstream wall and strange outlet.
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Old   November 29, 2010, 19:44
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Joshua Counsil
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Agreed with Glenn. Your domain is pretty tiny. You may be experiencing problems due to artificial truncation of the domain. Try making the domain larger in every direction.
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Old   December 2, 2010, 08:02
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this model is of a real device and we need to inspect it and insure the work that it will do. this device is a separator , so the pressure up the wing should be smaller the aht under it by an enough amount . but this is not the case here !

what do you think about the provided mesh above ? is it good or not? because that is the best one i can obtain from ANSYS CFX until now!
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Old   December 2, 2010, 14:24
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OK, I'll ignore the domain for now, but I can almost guarantee it's causing problems.

You can't properly judge a mesh from one picture or one simulation. You need to check its quality, refinement, and convergence. See: http://www.cfd-online.com/Wiki/Ansys_FAQ

For this type of simulation, I'd use a structured mesh, which the CFX built-in mesher cannot do. Use a program like ICEM. The advantages of a structured mesh are listed in the above link. It should be very easy to create a structured mesh for that domain due to its straight edges. At the very least, your boundary layer should be structured. Also, if the domain you're using represents a real device, then shouldn't the outside walls be viscous (and, therefore, have a refined boundary layer)? Whichever type of mesh you use, be sure to check the quality (e.g., aspect ratios, orthogonality... see link above).

You should create at least 3 meshes of varying density. Keep simulating until further mesh refinement does not significantly change the parameter(s) of interest (e.g., pressure distribution).

How's the convergence? What are your residuals like?
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