Hello all:

1) I need help regarding "shock-stability" and "convergence" problems during CFD simulation of internal supersonic flow in a wind-tunnel. 2). I am trying to fix-up the normal shock at particular locations (i.e. center of cavity) in a constant area test section to study shock-wave/boundary layer interactions(SWBLI). 3) I am varying the "back pressure" to change the shock-locations and speed. 4) But neither i am getting stable steady state solutions nor good convergence in mass & energy residuals 5). I need relevant literature sources or hints to track this problem. Help would be greatly appreciated. Thanks in advance, Regards.

You are looking at a difficult problem, especially if you are trying to capture the normal shock. Inherent dissipation in the solution scheme will tend to smear the normal shock and the growth of the wall boundary layer will tend to make the location of the normal shock be unstable (the displacement effect due to the boundary layer will make the inviscid flow similar to a converging duct, for which a standing normal shock is unstable - think of a converging inlet problem).

Two suggestions which may be helpful:

(1) instead of specifying back pressure, try fixing mass flow rate. They should be equivalent, but sometimes computationally a fixed back pressure will give you waves reflected from the boundary which may or may not settle out, especially with a standing normal shock.

(2) Try placing a computational/zonal boundary where the normal shock is supposed to be and write a boundary condition routine to impose the normal shock conditions across this boundary (allow for continuity in mass, momentum and energy flux, but discontinuity in primitive variables - density, pressure, velocity, etc.)

Hope this helps.

(1). Are you sure that you can get a normal shock stabilized in a constant area test section?

Hi Rajeev

I don't anything about SWTBLI but some days back I reached Prof D.Knight's website(Rutgers Univ)searching for some paper thru google. I browsed through his site. he's working on SWTBLI, u can download some papers from his site too. Hope this helps abhijit

Hi,

Thanks alot! I greatly appreciate you for understanding my problems and providing some lucrative hints and suggestions.

Thanks once again, Regards.

Hi Abhijeet:

Thanks alot. I got couple of useful papers from Prof. Knight web-page.

Thanks once again, Regards.

Hi, Abhijit

Please tell me the web site to download the papers you mentioned. Thanks in advance

Yong

Hi you can visit http://cronos.rutgers.edu/~mechaero/ & look for Prof D.Knight's website then it's there on his site under publications Abhijit

Hello John:

1) Yeah, i appreciate your doubts regarding stability of normal shock in a constant area duct. Even i was also wondering alot on that. 2) By the way, I am working on a project Mesoflaps aeroelastic transpiration (MAT) to control SWBLI in supersonic a/c inlet (without bleeding) 3). In UIUC, we have performed wind tunnel testing to control Normal and Oblique shock boundary layer interactions by means of mesoflaps over the cavity. 4). Briefly, I have experimental data for normal shock and boundary layer interaction near the cavity regions. In experiment, there is no problem in getting stable normal shock in the test section by means of varying "back pressure". Boundary layer development after the lambda shock helps in stabilizing the shock in test section. 5) Now I am simulating this case and want to make comparison between experiment and CFD data.

I hope this will help you to understand my problem. Regards, Rajeev.