I consulted several works but could not get any suitable reasoning for the reason of reattachment of the bubble downstream of the flow except the fact that the separated bubble reattaches in the fluid at a point, known as Saddle point. I am in search of physics of reattachment.
Hello Kumar,
In the presence of laminar-turbulent transition, flow may reattach (e.g. on wings of gliders) as follows: Initially laminar boundary flow may separate because of an adverse pressure gradient. Now the flow becomes strongly unstable and hence turbulent. Hence, it reattaches further downstream because of the stronger resistance of turbulent boundary-layer flow against separation.
Best regards, Johannes
Look at this link.Good luck.
http://www.bharath-lab.org/separating-and-reattaching-flows.html
I think it can be intuitively understood as follows: Flows separate in an adverse pressure gradient because the transport of wall-tangent momentum in wall-normal direction is not sufficient enough to counter the friction induced at the wall (or actually the vorticity generated at the wall). So the higher te wall-normal momentum transport, the further separation can be delayed. Off course turbulent flow is orders of magnitude better in wall-normal momentum transport than laminar flow. So when a laminar separation bubble is generated and the flow becomes turbulent further downstream (as Johannes pointed out), then you have a fair chance that the wall-normal momentum transport is able to induce wall-tangent flow again close to the wall, which is seen as reattachment in the flow.
Thank you Johannes, Zoubair and Arjan.
Your answers really added to my knowledge. Thanks again.
@ Johannes Zahn, I have a related question. If the flow is strictly laminar, is there still a possibility of re-attachment of a separated flow?
Dear Anand,
I was also wondering whether reattachment of the separated flow on the cylinder surface possible? If yes, what is the physics behind this?
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