External aero wall function selections for kw-SST and kE

aerogt3 · February 1, 2013, 09:01

Hello all,

I have done a lot of searching and found a lot of conflicting information from different time periods, foam releases, etc. I am pretty confused at this point. Basically what I am trying to do is run a case comparing two turbulence modeling approaches. My Reynold's number is about 1 million.

1.) kw-SST, with y+ < 1, and 20 prism layers
2.) realizable kEpsilon, with y+ > 30 and 5 prism layers

For scenario 1, I have full resolution of the boundary layer and do not want to use wall functions. So far, I am setting:
-omega to omegaWallFunction
-k and nut to fixedValue, where that value is very small (1e-09 ).
Is this reasonable, or are there better recommendations? If I am doing it correct, how should I set the fixed value for k and nut? Calculate them? Just set it to a small value arbitrarily?

For scenario 2, I have seen a lot of different options out there. I am using:
-kqRWallFunction for k,
-epsilonWallFunction for epsilon
-nutkWallFunction for nut.
Is this correct? I have read that nutLowReWallFunction and nutUSpaldingWallFunction would also be appropriate, but I don't understand what the difference would be (if any).

Many thanks for any advice on what is, for me at least, a very confusing topic!

maHein · February 1, 2013, 15:57

I can at least help you with your second scenario. The nutUSpalingWallFunction is based on Spaldings law of the wall which was developed for incompressible fluids. It is valid within the whole boundary layer.

kqRWallFuntion just implies a zeroGradient condition and is correct for k. epsilonWallFunction is also correct for epsilon. However, I'm think it's just valid for high-reynolds models.

nutLowReWallFunction simply sets the turbulent viscosity to zero at the wall. This boundary condition, as the name suggests, should only be used for lowRe models. The reason for this boundary condition is the access function to calculate y+, for example with the yPlusRAS tool.

February 1, 2013, 09:01	External aero wall function selections for kw-SST and kE	#1
aerogt3 Member Join Date: Mar 2009 Posts: 90 Rep Power: 17	Hello all, I have done a lot of searching and found a lot of conflicting information from different time periods, foam releases, etc. I am pretty confused at this point. Basically what I am trying to do is run a case comparing two turbulence modeling approaches. My Reynold's number is about 1 million. 1.) kw-SST, with y+ < 1, and 20 prism layers 2.) realizable kEpsilon, with y+ > 30 and 5 prism layers For scenario 1, I have full resolution of the boundary layer and do not want to use wall functions. So far, I am setting: -omega to omegaWallFunction -k and nut to fixedValue, where that value is very small (1e-09 ). Is this reasonable, or are there better recommendations? If I am doing it correct, how should I set the fixed value for k and nut? Calculate them? Just set it to a small value arbitrarily? For scenario 2, I have seen a lot of different options out there. I am using: -kqRWallFunction for k, -epsilonWallFunction for epsilon -nutkWallFunction for nut. Is this correct? I have read that nutLowReWallFunction and nutUSpaldingWallFunction would also be appropriate, but I don't understand what the difference would be (if any). Many thanks for any advice on what is, for me at least, a very confusing topic!

February 1, 2013, 15:57		#2
maHein Member Join Date: Jun 2012 Posts: 76 Rep Power: 14	I can at least help you with your second scenario. The nutUSpalingWallFunction is based on Spaldings law of the wall which was developed for incompressible fluids. It is valid within the whole boundary layer. kqRWallFuntion just implies a zeroGradient condition and is correct for k. epsilonWallFunction is also correct for epsilon. However, I'm think it's just valid for high-reynolds models. nutLowReWallFunction simply sets the turbulent viscosity to zero at the wall. This boundary condition, as the name suggests, should only be used for lowRe models. The reason for this boundary condition is the access function to calculate y+, for example with the yPlusRAS tool.