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LES outflow condition for a subsonic flat plate boundary layer

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Old   August 24, 2018, 23:00
Lightbulb LES outflow condition for a subsonic flat plate boundary layer
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Hello all!

I'm trying to use a compressible LES code to simulate a subsonic flat plate turbulent boundary layer. For the inflow, RRM(rescaling and recycling method) will be used, but I'm not sure how to give outflow condition. If the computational field is truncated at the end of the flat plate and no extra domain is connected behind, farfield pressure cannot be specified here, right?

Some paper used non-reflecting outflow and sponge layer was added, but it seems too complicated for me to understand the procedure(I'm a new learner )

I was wondering if the convective outflow can be applied in compressible flow? Is this outflow condition proper for my problem? Is there any reference for it?

Would you give me some advise? Thanks a lot!
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Old   August 25, 2018, 03:33
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Originally Posted by chris x View Post
Hello all!

I'm trying to use a compressible LES code to simulate a subsonic flat plate turbulent boundary layer. For the inflow, RRM(rescaling and recycling method) will be used, but I'm not sure how to give outflow condition. If the computational field is truncated at the end of the flat plate and no extra domain is connected behind, farfield pressure cannot be specified here, right?

Some paper used non-reflecting outflow and sponge layer was added, but it seems too complicated for me to understand the procedure(I'm a new learner )

I was wondering if the convective outflow can be applied in compressible flow? Is this outflow condition proper for my problem? Is there any reference for it?

Would you give me some advise? Thanks a lot!



For compressible flows, you have to follow the characteristic lines, therefore one condition must be fixed at the outlet as the characteristic enters into the domain.
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Old   August 25, 2018, 04:19
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For compressible flows, you have to follow the characteristic lines, therefore one condition must be fixed at the outlet as the characteristic enters into the domain.
Thank you for your reply. As far as I know in most cases, the outflow boundary is set far away from the main region and the pressure at the infinity will be specified. For the flat plate boundary layer however, if the outflow boundary is set right at the end of the plate, how can I specify this one fixed condition?
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Old   August 25, 2018, 05:09
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In the BL approximation, dp/dy->0, therefore you can set the external pressure
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