Near wall k in stand kepsilon
Hi,
I have a problem understanding the modelling of the kequation in the standard kepsilon model with wall functions (i.e. wall functions for the mean velocity): It is said that the full kequation is solved in the control volume adjacent to the wall, giving the kequation a boundary condition of zero normal flux at the wall. Normally the standard kepsilon model with wall functions is used with the cell center of the cell adjacent to the wall having a y+ value larger than say 11 or even larger. But it is found that k+ has a maximum at around y+=15 and falls steeply down when approaching the wall. Isn't this contradictory to the above mentioned solution method for the kequation? I mean how can you allow for a maximum for a function at y+=15 when your cell center of the control volume adjacent to the wall is at say y+=20?</div> I hope the problem in understanding I am having became clear.</div> Cheers Fabian 
Re: Near wall k in stand kepsilon
(1). Yes, you are looking in the right direction. (2). As a result, the computed TKE (k) distribution and level are not correct, normally. (3). If you are just a user of the code, do you care? If you are the vendor of the code, do you care? (4). It is not easy to predict the turbulence quantities , and normally they are not accurate. (the mean flow is somewhat less sensitive .) (5). Even with low Reynolds number models, the modeling of turbulent flows is still a research field.(PhD research subject) (6). By the way, I have said that CFD is a personal thing, and it is not CAD. If it can not meet your requirement, then it is not good for you. I think, I like your question.

Re: Near wall k in stand kepsilon
hi fabin,
What jhon has said is right. I would like to add something more. The emphasis in wall function approach is on getting good estimate of value of near wall gridpoint. the log law says that u can have ur first gridpoint from the wall anywhere between 11.6 and 100. As ur point shifts further u the value of k will decrease exponentially.It really does'nt matter if we do not capture the maximum atleast for highre non seperating flows. (this can be of serious consequence in seperated flows). As speaking of standard ke model there are lot of problems with it. hope this helps bye abhijit tilak 
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