Question about Wall function in CFX5.7
 

Hi everyone,

I recently found one article about "application of advanced wall functions to forced & mixed convection flows" by Dr Hector Iacovides at UMIST. He discussed about the different wall-function strategies-analytical wall functions that do not rely on the log law but solve the simplified momentum equation across the near-wall cells. The paper claimed that this approach is as computationally efficient as the standard wall function & yet has the quality of low-Re approach.

Anyone know if CFX has the similar wall function as well?

Thanks,Sam

Re: Question about Wall function in CFX5.7
 

The CFX equivalent is the bounded wall function which effectively caps the Y+ value at about 11 (the point where the log-law breaks down. Note: it's at this point that low-Re models kick in and integrate through the viscous sub layer). While it sounds crude it works quite well.

Re: Question about Wall function in CFX5.7
 

You are talking about the scalable wall functions. This is the default wall function when you run any of the epsilon based turbulence models in CFX-5. The underlying assumption is that the vertex at the wall is at the edge of the viscous sublayer and that you are not resolving the laminar region.

CFX-5 also has the automatic treatment available with the blended epsilon/omega models (eg: SST). With these models the flow solver will integrate to the wall where it can (i.e. where you have enough grid resolution to resolve the boundary layer) and use scalable everywhere else. It also blends to k-epsilon in the free stream where k-omega is known to not behave well.

In CFX-5.8 you will be able to override the wall functions for the epsilon based models. So, theoretically you could implement the UMIST treatment yourself if you felt that was necessary for you application.

Neale.