supersonic case with kOmegaSST

cfd.with.openfoam · October 18, 2013, 23:58

I am dealing with a supersonic case and I have a BL resolved grid (i.e y+ < 1 everywhere). Turbulence model being employed is kOmegaSST and the BCs that I am using for k, omega and mut, at the walls are -

k - 1e-10 (simply because viscosity takes charge at the wall)
omega - compressible

megaWallFunction (not sure about this)
mut - 1e-10 (no turbulence at the wall so no turbulent viscosity either)

Questions -

1. Henry mentioned in a couple of posts that if y+<1 then one should use a lowRe model. Another thing that he mentioned somewhere was that the kOmegaSST implemented in OpenFOAM (by the way right now I have OF-2.2.2) is not suitable for wall resolved calculations because some kind of damping is not there. So the question is - Is it OK to use kOmegaSST with y+<1 everywhere or not with OF-2.2.2?

2. If it is OK to use kOmegaSST in this scenario; then are the boundary conditions for k, omega and mut ok here or not?

Thanks very much.

I have read several threads and posts but these things are not clear at all to me.

Tobi · October 23, 2013, 08:48

Hi,

I am not sure if your post is correct in this subforum because your question is not depending on bugs but rather on turbulence models and it s wall functions.

If you use wall functions for the turbulent variables then you should have y+ > 12.4 ... have a look at different literature (for example Ferziger).

If you have y+ round about 1 then you do not Need wall functions because you are solving the whole wall field direct (viscouse sublayer). If you are using wall functions you use the logarithmic wall function to get the effects of the viscous sublayer.

So your omega wall function is wrong because you have y+ < 1.
You k value does not make sence to me?!

If i am wrong please correct me

(it s a long time ago I had the theoretics).

Regards Tobi

PS: @admin - maybe its better to move the last two Posts to a new thread to clean this on.

wyldckat · October 26, 2013, 13:18

FYI: I've moved the two posts indicated by Tobi from the thread http://www.cfd-online.com/Forums/ope...komegasst.html to this new one you are currently reading

October 18, 2013, 23:58	supersonic case with kOmegaSST	#1
cfd.with.openfoam Member Fluid Dynamics Join Date: Mar 2013 Posts: 41 Rep Power: 13	I am dealing with a supersonic case and I have a BL resolved grid (i.e y+ < 1 everywhere). Turbulence model being employed is kOmegaSST and the BCs that I am using for k, omega and mut, at the walls are - k - 1e-10 (simply because viscosity takes charge at the wall) omega - compressiblemegaWallFunction (not sure about this) mut - 1e-10 (no turbulence at the wall so no turbulent viscosity either) Questions - 1. Henry mentioned in a couple of posts that if y+<1 then one should use a lowRe model. Another thing that he mentioned somewhere was that the kOmegaSST implemented in OpenFOAM (by the way right now I have OF-2.2.2) is not suitable for wall resolved calculations because some kind of damping is not there. So the question is - Is it OK to use kOmegaSST with y+<1 everywhere or not with OF-2.2.2? 2. If it is OK to use kOmegaSST in this scenario; then are the boundary conditions for k, omega and mut ok here or not? Thanks very much. I have read several threads and posts but these things are not clear at all to me.

October 26, 2013, 13:18		#3
wyldckat Retired Super Moderator Bruno Santos Join Date: Mar 2009 Location: Lisbon, Portugal Posts: 10,975 Blog Entries: 45 Rep Power: 128	FYI: I've moved the two posts indicated by Tobi from the thread http://www.cfd-online.com/Forums/ope...komegasst.html to this new one you are currently reading Tobi likes this.

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October 23, 2013, 08:48		#2
Tobi Super Moderator Tobias Holzmann Join Date: Oct 2010 Location: Tussenhausen Posts: 2,708 Blog Entries: 6 Rep Power: 51	Hi, I am not sure if your post is correct in this subforum because your question is not depending on bugs but rather on turbulence models and it s wall functions. If you use wall functions for the turbulent variables then you should have y+ > 12.4 ... have a look at different literature (for example Ferziger). If you have y+ round about 1 then you do not Need wall functions because you are solving the whole wall field direct (viscouse sublayer). If you are using wall functions you use the logarithmic wall function to get the effects of the viscous sublayer. So your omega wall function is wrong because you have y+ < 1. You k value does not make sence to me?! If i am wrong please correct me (it s a long time ago I had the theoretics). Regards Tobi PS: @admin - maybe its better to move the last two Posts to a new thread to clean this on.