how can i impose a pressure boundary condition when i'm using onservation variables

What do u mean by conservation variables? And what kind of flows are u trying to simulate : incompressible or compressible....

Conservative variables are rho, rho*U, rho*V, and \rho E, which are often used as dependent variables to be solved for compressible flows and imply quantity per unit volume. The boundary contidions state their own, irrespetive of conservative or not. Therefore you can use pressure or temperature or velocity or other BC conditions, which may appear in a BC specification.

yes your definition of the conservation variables are true, sir, but i still don't know how to impose this boundary condition.

NOTE: I'm using Finite Element techniques!!!

Hi Guirguis,

the theory of setting boundary conditions is a complex subject and therefore I cannot give any recipe out of my head.

Anyway, I assume you know that prescribing pressure is the correct physical boundary condition. In Hirsch "Numerical Computation of Internal and External Flows" Vol. 2 you can find in Chapter 19 a in-depth discussion on how to set boundary conditions. In particular, Hirsch discribes how to transform boundary conditions given in one set of variables (e.g. primitive vars) into another set of variables (e.g. conservative). The only drawback of the sited reference is that it deals with Euler equations. An extension to Navier-Stokes is given in T. Poinsot and S. Lele. "Boundary conditions for direct simulations of compressible viscous flows." Journal of Computational Physics, vol.101(1):104-129

Hope that helps.

Have fun, Alan

Thank you Alan for your help. I solved my problem with home made technique. BUT it was very useful when I went to the library and took a look on Hirsch. It is an excellent book for finite difference techniques.

Also I recommend Chung, T. J. "Computational Fluid Dynamics". This book is ann excellent one too. It covers finite difference, finite element, and finite volume all with semi equal depth.

I hope everyone have fun with CFD.

BYE