Boundary layer thickness of cylinder

Asiap · March 4, 2019, 15:28

Hi,

I am simulating air flow past cylinder and I wanted to calculate analytically the boundary layer thickness, just to compare it with what I got from Fluent. So I found this formula: δ ≈ 4,91√(νx/u) but I read it is applicable for flat plates. So my question is: can I apply this formula to a cylinder? And if yes, then my second question is: does x in the formula refer to the distance along the surface of the cylinder ex. half the circumference or rather the distance "across" the cylinder (I mean straight in the direction of the flow) ex. diameter?

I would be very grateful for any reply!
Regards,
Asia

FMDenaro · March 4, 2019, 15:43

No, you cannot use the BL theory over a flat plate

Asiap · March 4, 2019, 15:58

You meant I cannot apply it to the cylinder, didn't you? Cuz you wrote "flat plate" and my question is about cylinder.
Anyway, thanks for reply!

FMDenaro · March 4, 2019, 16:04

Quote:

Originally Posted by Asiap

You meant I cannot apply it to the cylinder, didn't you? Cuz you wrote "flat plate" and my question is about cylinder.
Anyway, thanks for reply!

yes, you can't use the theory valid for the semi-infinite flate plat for the case of a flow over a cylinder

Asiap · March 4, 2019, 16:11

Is there any formula for the boundary layer thickness in the case of a cylinder then?

agd · March 4, 2019, 21:52

Do a search for Thwaites method.

March 4, 2019, 15:28	Boundary layer thickness of cylinder	#1
Asiap New Member Joanna Pazdur Join Date: Mar 2019 Posts: 3 Rep Power: 7	Hi, I am simulating air flow past cylinder and I wanted to calculate analytically the boundary layer thickness, just to compare it with what I got from Fluent. So I found this formula: δ ≈ 4,91√(νx/u) but I read it is applicable for flat plates. So my question is: can I apply this formula to a cylinder? And if yes, then my second question is: does x in the formula refer to the distance along the surface of the cylinder ex. half the circumference or rather the distance "across" the cylinder (I mean straight in the direction of the flow) ex. diameter? I would be very grateful for any reply! Regards, Asia

March 4, 2019, 21:52		#6
agd Senior Member Join Date: Jul 2009 Posts: 351 Rep Power: 18	Do a search for Thwaites method. aero_head likes this.

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March 4, 2019, 15:43		#2
FMDenaro Senior Member Filippo Maria Denaro Join Date: Jul 2010 Posts: 6,768 Rep Power: 71	No, you cannot use the BL theory over a flat plate

March 4, 2019, 15:58		#3
Asiap New Member Joanna Pazdur Join Date: Mar 2019 Posts: 3 Rep Power: 7	You meant I cannot apply it to the cylinder, didn't you? Cuz you wrote "flat plate" and my question is about cylinder. Anyway, thanks for reply!

March 4, 2019, 16:11		#5
Asiap New Member Joanna Pazdur Join Date: Mar 2019 Posts: 3 Rep Power: 7	Is there any formula for the boundary layer thickness in the case of a cylinder then?