pipe shock problem

test3r · August 24, 2011, 07:32

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

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.

August 24, 2011, 07:32	pipe shock problem	#1
test3r New Member Thomas Join Date: Aug 2011 Posts: 11 Rep Power: 14	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

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
analytical solution of 1D shock tube problem	ma	Main CFD Forum	10	May 11, 2015 05:20
using ghost fluid method in shock tube problem	Amir	Main CFD Forum	4	February 24, 2011 10:09
Shock tube problem	ger	Main CFD Forum	1	September 24, 2003 07:41
CV problem with a long pipe..	rosco	FLUENT	10	May 6, 2003 13:48
looks simple,but confusing,a pipe flow problem!	W.Z.H	FLUENT	14	March 14, 2003 07:27

August 24, 2011, 07:44		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,701 Rep Power: 143	Post an image of what you get. And the CCL file.

August 24, 2011, 18:49		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,701 Rep Power: 143	Your image looks like it shows a shock wave at the end of the Mach 5 section to me.

August 24, 2011, 19:00		#5
test3r New Member Thomas Join Date: Aug 2011 Posts: 11 Rep Power: 14	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"?

August 24, 2011, 19:03		#6
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,701 Rep Power: 143	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

August 24, 2011, 19:29		#7
test3r New Member Thomas Join Date: Aug 2011 Posts: 11 Rep Power: 14	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?

August 24, 2011, 19:49		#8
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,701 Rep Power: 143	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.