Yeah sure - just thought he wanted the link. Well in the beginning the mention "It is based on my personal experience". Otherwise i guess that people seem to agree that it is typo.

Hi I am modelling flow past a sphere in openFoam and would like to simulate the same in steady state...I tried using kw-sst-model but for a reynolds no of 400000 the drag coefficint is coming out to be 0.3 which does not match with the literature at all...which model should I use for such cases?

I am using steady state RANS for now

something like reynolds stress model or Spalart-Allmaras might be worth looking into

I would highly assume that Re=4e5 would require a transient simulation with Co<1. The setup it self is unsteady by nature. You will probably have to track the drag-coefficent over a certain time and average.

Hi guys, I've once again thought a little bit more about the turbulence handling in my simulation. I have compared both highRE and lowRE modelling of the wall and wanted to clear something up, because on the forums there is conflicting information and a lot of stuff thrown around. If I want openFOAM to correctly handle the wallfunctions (.com and v2506) how do I defne it correctly?

Curently for the highRE I have:

k
kqRWallFunction with the internalfield value of 0.5

nut
nutkWallFunction with uniform 0

omega
omegaWallFunction with internal field of 2.7

for the lowRE case:

k
kqRWallFunction with uniform 1e-10

nut
nutUSpaldingWallFunction with uniform 0;

omega
omegaWallFunction with uniform 1e-4;

Does this go in the right direction? I am just a little confused with all the information on the web that conflicts itself and is from all over the years. Would appreciate it.

Kqr wall function is basically just a zero gradient BC

That's good for high re, but had for low re

I think, I'll double check

Both Spalding and omega wall function are fine for low re and high re

Yeah you want fixed value of 0 for k

If you know y+<1

There's also the kLowReWallFunction to complicate things as well

Which I guess might be the best one to use if you have a range of y+ values

Im looking at y+ from 0.5 to at most 8 but 95% up to 5 at most

Meaning i should be in the viscous sublayer

I do remember the userguide saying that kqRWallFunction holds for both cases aswell but i couldnt quite comprehend what the guide says sometimes and what is actually being applied

Yeah this is something I've run into before, there's seemingly no good or clear guidance on what you're supposed to do

But the logic is this - for low re conditions, you have 0 velocity at the wall, so therefore you must have 0 tke

so the appropriate boundary condition is TKE = 0

For high re, k in the first cell is determined by the wall functions, and so you don't want the boundary condition to interfere with that value, so you set zeroGradient

I assume kLowRe is intended to blend between those two somehow - but I haven't looked at the derivation much

From the theory this is because of the laminar sub layer that we are resolving right? If its laminar there is no need to calculate any turbulent quantities

But thanks for the info, I will just change the k BC to fixedValue of 0 and see how much that effects things.

Yes

If U=0, k=0

What is the difference between nutUSpalding and nutkWall, because both apparently should account for high and low y+ values, or in my case can I once again force it to a specific uniform fixed value because I resolve the wall? Nu_t should effect my flow behavior more than k and now theres questions rising for that aswell.

If I'm not mistaken, nutU, nutUSpalding and nutk should all account for high/low Re, but they use different variables to compute nut (based on U or k)

Theoretically then they should converge to the same solution?

Is there a general rule I can follow to apply them, say U instead k assuming it provides more accurate numbers