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 student December 26, 2006 00:05

backward facing step flow

im solving backward facing step flow.....how to give boundary condition at the exit. at the exit dp/dx=0 from y=0 to y=H or p=0 from y=0 to y=H im considering the flow is fully developed so at the exit du/dx=0 and dv/dx =0 at the top and bottom walls dp/dy=0 u= v=0 (no slip boundary condition)

at the inlet im giving a parabolic profile before the expansion. please give me the correct boundary condition for pressure. thanks in advance.

 Josyula March 31, 2009 06:56

Quote:
 Originally Posted by student ;47161 im solving backward facing step flow.....how to give boundary condition at the exit. at the exit dp/dx=0 from y=0 to y=H or p=0 from y=0 to y=H im considering the flow is fully developed so at the exit du/dx=0 and dv/dx =0 at the top and bottom walls dp/dy=0 u= v=0 (no slip boundary condition) at the inlet im giving a parabolic profile before the expansion. please give me the correct boundary condition for pressure. thanks in advance.
Hi,
Do you have the C or FORTRAN code for the 2-D unsteady backward facing step in FDM/FVM scheme ?

 maysmech February 27, 2011 03:44

Quote:
 Originally Posted by student ;47161 im solving backward facing step flow.....how to give boundary condition at the exit. at the exit dp/dx=0 from y=0 to y=H or p=0 from y=0 to y=H im considering the flow is fully developed so at the exit du/dx=0 and dv/dx =0 at the top and bottom walls dp/dy=0 u= v=0 (no slip boundary condition) at the inlet im giving a parabolic profile before the expansion. please give me the correct boundary condition for pressure. thanks in advance.
Hi,:)

I have these questions too.
I want use Driver and Seegmiller Paper.

What is the inlet turbulence? it is not mentioned on paper.
What should be set for outlet.
what is inlet k and epsilon for this paper?

Regards.

 Kyounghwa January 21, 2012 09:17

Help me.

Quote:
 Originally Posted by Josyula (Post 211388) Hi, Do you have the C or FORTRAN code for the 2-D unsteady backward facing step in FDM/FVM scheme ?
Hello. I'm Kyounghwa.
I have same question.

I have the C code and FDM scheme by projection method.
I give inlet and outlet as follows.

Inlet : u_mean=1, u_max=3/2;
Outlet : u_mean=1, u_max=3/4;

The hight of domain is 2.
The inlet size is 1 and outlet size is 2.

Am I wrong?

ps : I'm reading "A numerical revisit of backward-facing step flow problem" by T.P.Chiang and Tony W.H. Sheu. in 1999.

 Kyounghwa January 23, 2012 10:41

Does anybody know?

Does anybody know?

 rmh26 February 17, 2012 11:54

You should look into the open/traction boundary condtion for this sort of flow through situation. A Recent paper "Improvements on open and traction boundary condtions for the NS time splitting methods" by A.Poux JCP 2011

But I guess a simpler answer is that if the flow is steady and parabolic at the outlet then P = 0 at the outlet is ok but the you might be constraining the flow by setting du/dx = 0.
Try extending the domain a little and seeing if the flow changes. Specifically the condition du/dx is not appropriate if you are near the recirculation zone or have any vortex shedding and you can't really be sure that you aren't artificially shortening the recirculation zone by imposing that condition without doing domain independence studies.

BTW I have done this sort of study recently for the axisymmetric case (flow through an expansion) and I using the du/dx = 0 and p = 0 at the exit condition with a long domain if you want to compare results or have further questions.

 sahand saghari June 9, 2013 11:17

Quote:
 Originally Posted by Josyula (Post 211388) Hi, Do you have the C or FORTRAN code for the 2-D unsteady backward facing step in FDM/FVM scheme ?
hi