There is big difference in reattachment length for computational and experimental stu

ahmeterko · July 9, 2023, 05:26

Hello everyone!

I am studying on an unsteady Backward Facing Step (BFS) flow. My reference experimental study is the Li et al. (2020) "Effect of periodic perturbations on the turbulence statistics in a backward-facing step flow". In my results, there is a big difference in reattachment length compared the reference study. Reattachmen length is 4.2h in experimental study but in my study reattachment length is the 5.6. Is big difference between experimental and computational study normal?

LuckyTran · July 9, 2023, 20:20

In short yes, there can be massive differences in reattachment lengths depending on which models you use. k-epsilon is notorious for being borderline completely wrong.

However, you should keep in mind that reattachment length determined experimentally may be different than how it is determined in CFD. Experimenters and CFD'ers often have different definitions that can also lead to a 1h difference. Keep in mind reattachment should not be viewed as a phenomenon occurring at a well defined point in space, but a fuzzy area.

ahmeterko · July 11, 2023, 11:54

Thanks for help

July 9, 2023, 05:26	There is big difference in reattachment length for computational and experimental stu	#1
ahmeterko New Member ahmet Join Date: May 2023 Posts: 4 Rep Power: 3	Hello everyone! I am studying on an unsteady Backward Facing Step (BFS) flow. My reference experimental study is the Li et al. (2020) "Effect of periodic perturbations on the turbulence statistics in a backward-facing step flow". In my results, there is a big difference in reattachment length compared the reference study. Reattachmen length is 4.2h in experimental study but in my study reattachment length is the 5.6. Is big difference between experimental and computational study normal?

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July 9, 2023, 20:20		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,753 Rep Power: 66	In short yes, there can be massive differences in reattachment lengths depending on which models you use. k-epsilon is notorious for being borderline completely wrong. However, you should keep in mind that reattachment length determined experimentally may be different than how it is determined in CFD. Experimenters and CFD'ers often have different definitions that can also lead to a 1h difference. Keep in mind reattachment should not be viewed as a phenomenon occurring at a well defined point in space, but a fuzzy area.

July 11, 2023, 11:54		#3
ahmeterko New Member ahmet Join Date: May 2023 Posts: 4 Rep Power: 3	Thanks for help