CFD Online Discussion Forums - Pressure transmissive bc

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Hi Patty,

just for completeness. A more handsome way to optimize your Linf might be a FFT of your problem and adapting Linf to a value the main wave length fits into at least once.

Quote:

to have "buffer zones", I suppose you mean increasing the NUMBER of cells close to the outlet? It it so?

:eek:Absolutely not! :eek:
You should increase the cell size (Max ratio 1.2) in the travelling wave direction until you reach something like 10-20 cells per critical wavelength and then let it travel one or more periods.

CJA :D

Quote:

Originally Posted by woody (Post 294341)

Hi Bertrand,

I figured it out. Do you have the Paper Boundary conditions for direct simulations of compressible viscous flows
T. J. Poinsot* and S. K. Lelef†
Center for Turbulence Research, Stanford University, Stanford, California 94305, USA
NASA Ames Research Center, Moffett Field, California 94305, USA

Received 23 February 1990;
Revised 12 April 1991.
Available online 24 September 2004.
of Poinsot & Lele

It is simply inserting the two LODI formulations (Eqs. 25+34) by eliminating L1. You receive a differential equation in p. L5 is replaced by K/Linf(p-pinf).
Then you have to reformulate it as a mixed BC.

Hope this helps

Tobias

Hi, I think L1 is replaced by K(p-pinf)/Linf.

Question about how to implement Open Atmosphere

Hi Everyone, Thanks for your discussion on waveTransmissive BC, I learned a lot.
Basically I'm trying to use Open atmospheric BC in a Shear-Layer case, and based on the papers I studied (Stanley and Sarkar) I have to use a non-reflective BC for sides and outlet. For pressure I`m sure wave transmissive is a good BC. but for others I have questions. I have tried BCs like inletOutlet and zeroGradient for U, but they don't give a good result.
The problem is when I studied the paper by Poinsot and Lele, which you've discussed here, it mentions that we have to use LODI equations to solve for L1-L5 . For variables, like P,V and T we have to solve for their characteristic equations in time based on L1-L5. Also we have to implement zeroGradient BCs for viscous stresses.
This is discussed in the paper by Poinsot and Lele in page 115 section 3.2 "A subsonic non-reflecting outflow." For step 2 it says we put for L1 (as I mensioned above) :

L1=K(p-p_Inf)

and

K=Sigma(1-Ma^2)c/L_inf

( proposed by Rudy and Strikwerda)
then we solve for eqs 9-13 to get values at BCs.
My Question is which OpenFOAM Boundary condition is the same as above, and how should I implement the zero gradient terms for Viscous Stresses. If the waveTransmissive does this for all of them (solves the equations for each variable ) how should I describe the BC for U and T in OpenFOAM?

Hi Ali,

I am trying to help you, but unfortunately this would recommend to much information for a discussion forum.

Just relaxing, that is what waveTransmissive does, U and especially T does not make sense since it is an outlet. Concerning your Viscous Stresses problem, I am not the man to ask.

Generally I would recommend to read the papers of Yoo and Im 2005, and 2010 (Combustion Theory and Modelling) and Lodato and Vervisch 2008 (J. of Computational Physics) about NSCBCs.

Nevertheless we are working on an implementation of these boundary conditions, but it might take up to a year to publish them....

Regards Tobias

Quote:

Originally Posted by woody (Post 305880)

Hi Tobias,
I am wondering if you already published your boundary conditions what you have mentioned in your post. If yes, could you please send me a link or copy of the article.
Thanks in advance.
M K Singh