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-   -   pipe shock problem (http://www.cfd-online.com/Forums/cfx/91835-pipe-shock-problem.html)

test3r August 24, 2011 07:32

pipe shock problem
 
Hello

I am computing 1/6 of a pipe with a restriction inside. The material is air. As a BC I use a pressure difference of 1 bar between the inlet and outlet. (Advection and Turbulence Scheme: High Resolution) This results in a Mach number of 5.
I expect a shock after the restriction but unfortunately there is no. Does somebody know which options I have to change to get the shock?
Thanks for helping!

Regards

ghorrocks August 24, 2011 07:44

Post an image of what you get. And the CCL file.

test3r August 24, 2011 08:09

1 Attachment(s)
This is one of the results I got.

ghorrocks August 24, 2011 18:49

Your image looks like it shows a shock wave at the end of the Mach 5 section to me.

test3r August 24, 2011 19:00

Thanks for looking. In contrast to real experiments the shock should start earlier. Further the influence to the upper area is too small. Do you have an idea to improve the shock "qualitiy"?

ghorrocks August 24, 2011 19:03

So your problem is accuracy, not that the shock does not appear.

Try the suggestions here:
http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F

test3r August 24, 2011 19:29

Thus you think there is a shock? I am not quite sure.
At the moment I am working at a sensitve analysis. I think the grid is fine but I will test a much finer one. I will report about the result.
Do you think the timestep size could be the right influence parameter?

ghorrocks August 24, 2011 19:49

It looks like a shock wave, but I do not have the data set in front of me so I cannot check. If you do not think it is a shock then post an image which shows it.

The FAQ explains the key general issues required for an accurate CFD analysis. I recommend you work through the suggestions.


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