# How to do analysis at backward facing step

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 December 8, 2011, 09:51 How to do analysis at backward facing step #1 New Member   Join Date: Nov 2011 Posts: 24 Rep Power: 14 Image above is Backward Facing Step. The upper side is inlet, the lower side is outlet. I need to do analysis at the step height area. Is there any analysis I can perform? I was told to do analysis of wall shear, mass flow, shear stress, shear strain and velocity. I already done velocity by using graph a line, contour and streamline. Please enlight me for the other analysis. Thanks in advanced.

 December 8, 2011, 16:34 #2 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143 There are millions of academic paper analysing this flow. have a look at some and see what they use as their key flow parameters.

 December 11, 2011, 04:12 #3 New Member   Join Date: Nov 2011 Posts: 24 Rep Power: 14 Thanks. I get some idea now. However, I have difficulties at finding the vortex at the step area. From picture above, right side is inlet, left side is outlet. I do streamline using cfx, and it's 3D streamline start from inlet. The variable is velocity. How do I make cfx to 'sketch' the vortex at step area? It's 500 Reynolds Number by the way, and fluid self-circulation should exist at step height. Is there any method for me to view the vortex/self-circulation at step? Thanks in advanced. By the way I am using ANSYS 11.0.

December 11, 2011, 10:02
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Sijal
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another method is to use the tecplot or feildview, you will get very nice pictures
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 December 11, 2011, 18:04 #5 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,703 Rep Power: 143 You do not need tecplot or fieldview for this, CFD-Post will do it just fine. You need to think laterally a bit to show some of these features. If you want the separation length then look at the u velocity on the bottom wall. The point which has zero u velocity is the separation reattachment point. If you want a picture which shows the recirculation then simply put some streamline seed points in the separation region. You can do this either manually, or using the domain with a reduction factor. Adjust the reduction factor to give you a few points in the recirculation region but not too many points. Far: Your image with a release point will not work. streamlines started from your line will simply jump over the separation region. You need to seed streamlines inside the separation region.

 December 21, 2011, 06:50 #6 New Member   Join Date: Nov 2011 Posts: 24 Rep Power: 14 Reduction factor 1.0 did shown recirculation zone at step height. Thanks a lot.