Boundary Layer & Wall Treatment

GRAUPS · September 14, 2012, 19:48

Hey guys, I've recently started solving some simple models within OpenFOAM to see I could match the same model made and solved in Fluent. One of the most common differences I'm seeing is in wall treatment. It is illustrated in the velocity profile below...

vel _com.jpg

Fluent has a well defined boundary layer and seems to apply the no slip boundary condition very well. Where as in OF it almost appears as if it's applying a slip boundary condition. I'm using OF 2.1.1 and rhoPorousMRFSimpleFoam as the solver. The turbulence model I'm currently using is kEpsilon. My initial wall boundary conditions are outlined below...

U - fixedvalue uniform 0
p - zeroGradient
T - zeroGradient
k - compressible::kqRWallFunction uniform 14
epsilon - compressible::epsilonWallFunction uniform 1500
alphat - alphatWallFunction uniform 0
mut - mutkWallFunction uniform 0

I've set the viscosity using sutherland transport to that of air in the thermophysicalProperties file...

transport
{
As 1.716e-5;
Ts 273.11;
}

The case converges very well in both Fluent and OF, however, I'd like to see better wall treatment in OF. Has anyone else had this problem and can anyone shed any light on what I may be doing wrong? Are there different wall functions I should be using to get better behavior? Let me know if I need to provide any additional information. Thanks!

doubtsincfd · October 16, 2012, 00:16

are are your schemes second order?
I have observed that there is a big variation in the profile when you switch from 1st to second order.

Also, have you monitored the pressure at inlet.
I am simulating a case with rhoporusmrfsimplefoam and the case converges but the absolute pressure oscillates between for a long time before converging. The sad part is, the oscillations are in negative zone also (negative absolute pressure) which is absurd.

September 14, 2012, 19:48	Boundary Layer & Wall Treatment	#1
GRAUPS Member Brock Lee Join Date: Sep 2012 Location: Midwest Posts: 40 Rep Power: 14	Hey guys, I've recently started solving some simple models within OpenFOAM to see I could match the same model made and solved in Fluent. One of the most common differences I'm seeing is in wall treatment. It is illustrated in the velocity profile below... vel _com.jpg Fluent has a well defined boundary layer and seems to apply the no slip boundary condition very well. Where as in OF it almost appears as if it's applying a slip boundary condition. I'm using OF 2.1.1 and rhoPorousMRFSimpleFoam as the solver. The turbulence model I'm currently using is kEpsilon. My initial wall boundary conditions are outlined below... U - fixedvalue uniform 0 p - zeroGradient T - zeroGradient k - compressible::kqRWallFunction uniform 14 epsilon - compressible::epsilonWallFunction uniform 1500 alphat - alphatWallFunction uniform 0 mut - mutkWallFunction uniform 0 I've set the viscosity using sutherland transport to that of air in the thermophysicalProperties file... transport { As 1.716e-5; Ts 273.11; } The case converges very well in both Fluent and OF, however, I'd like to see better wall treatment in OF. Has anyone else had this problem and can anyone shed any light on what I may be doing wrong? Are there different wall functions I should be using to get better behavior? Let me know if I need to provide any additional information. Thanks!

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October 16, 2012, 00:16		#2
doubtsincfd Senior Member Join Date: Nov 2009 Location: Michigan Posts: 135 Rep Power: 17	are are your schemes second order? I have observed that there is a big variation in the profile when you switch from 1st to second order. Also, have you monitored the pressure at inlet. I am simulating a case with rhoporusmrfsimplefoam and the case converges but the absolute pressure oscillates between for a long time before converging. The sad part is, the oscillations are in negative zone also (negative absolute pressure) which is absurd.