How to do analysis at backward facing step

warlocklw · December 8, 2011, 10:51

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

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.

December 8, 2011, 10:51	How to do analysis at backward facing step	#1
warlocklw New Member Join Date: Nov 2011 Posts: 24 Rep Power: 15	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.

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December 8, 2011, 17:34		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,854 Rep Power: 144	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, 05:12		#3
warlocklw New Member Join Date: Nov 2011 Posts: 24 Rep Power: 15	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, 19:04		#5
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,854 Rep Power: 144	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, 07:50		#6
warlocklw New Member Join Date: Nov 2011 Posts: 24 Rep Power: 15	Reduction factor 1.0 did shown recirculation zone at step height. Thanks a lot.