# Y+ for K omega SST in a micro channel with surface roughess not coming out.

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• Last Post 28 April 2019
jonheb posted this 14 February 2018

Hi there I was wondering if you could help me out with a similar problem.

I am modelling a micro channel with k omega SST turbulence and there is a constant heat flux also added at the wall of my micro channel.

I have modelled the micro channel as a smooth flow initially and have been getting a Y+ of 1 for Reynolds of 40k approx., but when I add a roughness ks of 9.84e-5 the Y+ is now 200+. I don't understand what I need to do in order to get it back to Y+=1 again, I have played with the bias of the mesh and tried increasing the number of cells but very little happens.

I am trying to see the sublaminar layer in so that I can see the effects of heat transfer.

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Raef.Kobeissi posted this 27 February 2018

hI,

Adding wall roughness does affect the Y+ Value. To understand the relationship I advise you to read the documentation.

Regards

Raef Kobeissi

mdfaizan444 posted this 11 January 2019

hey, i am working in a wavy channel in which i want to calculate y+ value... i tried to calculate from your website but it requires boundary layer length that i not know.. so plz help me regarding this.  And also how to calculate the Nussult number in 2D flow, like as 3D flow will it be calculated from area weighted average?

abenhadj posted this 11 January 2019

For channel there is some other correlations to get the friction factor. Check the blog of our partner: https://www.computationalfluiddynamics.com.au/tips-tricks-cfd-estimate-first-cell-height/

Best regards, Amine

LorenzoMazzei posted this 28 April 2019

hI,

Adding wall roughness does affect the Y+ Value. To understand the relationship I advise you to read the documentation.

Regards

Actually, the virtual wall shift approach should change the y+ value given the ks+ value. At that point the shear should be calculated depending on the new y+ value, using wall integration or wall function. Am I right?

abenhadj posted this 28 April 2019

Yes.

Best regards, Amine

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