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warlocklw December 8, 2011 10:51

How to do analysis at backward facing step
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.

ghorrocks December 8, 2011 17:34

There are millions of academic paper analysing this flow. have a look at some and see what they use as their key flow parameters.

warlocklw December 11, 2011 05:12

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.

Far December 11, 2011 11:02

1 Attachment(s)
release pathlines from adjacent location
another method is to use the tecplot or feildview, you will get very nice pictures

ghorrocks December 11, 2011 19:04

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.

warlocklw December 21, 2011 07:50

Reduction factor 1.0 did shown recirculation zone at step height. Thanks a lot.

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