Wall functions for y+ < 1

y.liu · December 9, 2022, 15:10

Hi guys,

I'm trying to run an LES Smagorinsky simulation where my average y+ is 0.74 and my max y+ is 2.

These are low y+ values, so I've read that I don't need a wall function.

Is there any reason why I shouldn't use a wall function (nutUSpaldingWallFunction for example), since it gives me accurate results anyway?

sbaffini · December 10, 2022, 05:34

I don't remember the details for OF wall functions but, if a wall function is an all y+ one then, for low y+ values it just behaves as if it was off.

For the static Smagorinsky model, you should also check that OF has some damping function near walls for the turbulent viscosity, as it is known to produce the wrong near wall behavior.

These aspects could or not actually be relevant for your case depending from how important the wall turbulence production is in the overall flow mechanism at play. This, in addition to the discretizazion, of course.

December 9, 2022, 15:10	Wall functions for y+ < 1	#1
y.liu New Member Yicong Join Date: Nov 2022 Posts: 2 Rep Power: 0	Hi guys, I'm trying to run an LES Smagorinsky simulation where my average y+ is 0.74 and my max y+ is 2. These are low y+ values, so I've read that I don't need a wall function. Is there any reason why I shouldn't use a wall function (nutUSpaldingWallFunction for example), since it gives me accurate results anyway?

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December 10, 2022, 05:34		#2
sbaffini Senior Member Paolo Lampitella Join Date: Mar 2009 Location: Italy Posts: 2,195 Blog Entries: 29 Rep Power: 39	I don't remember the details for OF wall functions but, if a wall function is an all y+ one then, for low y+ values it just behaves as if it was off. For the static Smagorinsky model, you should also check that OF has some damping function near walls for the turbulent viscosity, as it is known to produce the wrong near wall behavior. These aspects could or not actually be relevant for your case depending from how important the wall turbulence production is in the overall flow mechanism at play. This, in addition to the discretizazion, of course.