Developed turbulent boundary layer simulation on flat plate

Turbulent · June 8, 2015, 06:50

Hello,

I'm doing a RANS simulation of a developed turbulent boundary layer on a 3-D flat plate. I've assumed a certain thickness for the BL at the inflow and correspondingly defined the inflow velocity profile.

My question is how can I define a pre-calculated shear stress only at x=0 (to simulate a certain shear stress at a given location of developed BL) while the rest of the plate will remain as no-slip wall. Avoiding this will cause a jump in the shear stress near the LE just like in normal BL development.

Thanks,

Jack

ghorrocks · June 8, 2015, 07:30

You could make a separate wall boundary for the first element which you define as a slip wall (or a wall with a defined wall shear stress if you prefer). Then the rest of the wall can be a normal wall boundary condition.

Turbulent · June 8, 2015, 12:41

Hi Glenn,

I've tried your suggestion but it seems that specifying pre-defined shear on the first cell stripe did not helped much... there's still a jump in the shear stresses distribution near the LE and the solution was poorly converged. What do you think?

Thanks,
Jack

ghorrocks · June 8, 2015, 20:46

First of all, check your simulation accuracy: Mesh, convergence, time step, etc. Unless they are under control anything could happen.

Assuming they are under control: I would compare the fully developed BL you have generated to one which CFX generates with a simulation. Are they the same?

June 8, 2015, 06:50	Developed turbulent boundary layer simulation on flat plate	#1
Turbulent New Member Jack B. Join Date: Apr 2009 Posts: 24 Rep Power: 17	Hello, I'm doing a RANS simulation of a developed turbulent boundary layer on a 3-D flat plate. I've assumed a certain thickness for the BL at the inflow and correspondingly defined the inflow velocity profile. My question is how can I define a pre-calculated shear stress only at x=0 (to simulate a certain shear stress at a given location of developed BL) while the rest of the plate will remain as no-slip wall. Avoiding this will cause a jump in the shear stress near the LE just like in normal BL development. Thanks, Jack

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June 8, 2015, 07:30		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,854 Rep Power: 144	You could make a separate wall boundary for the first element which you define as a slip wall (or a wall with a defined wall shear stress if you prefer). Then the rest of the wall can be a normal wall boundary condition.

June 8, 2015, 12:41		#3
Turbulent New Member Jack B. Join Date: Apr 2009 Posts: 24 Rep Power: 17	Hi Glenn, I've tried your suggestion but it seems that specifying pre-defined shear on the first cell stripe did not helped much... there's still a jump in the shear stresses distribution near the LE and the solution was poorly converged. What do you think? Thanks, Jack

June 8, 2015, 20:46		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,854 Rep Power: 144	First of all, check your simulation accuracy: Mesh, convergence, time step, etc. Unless they are under control anything could happen. Assuming they are under control: I would compare the fully developed BL you have generated to one which CFX generates with a simulation. Are they the same?