Hi everyone!

I am working with an axial pump in TASCflow at low Reynolds and I am using a Reynolds stress model (RSM). I am looking for the best solution for my problem.

In Near Wall Model, in advanced, there are two options: Log Law (standard) and Log Law (scalable).

I would like to know which is the difference between both options, and the concept of these, and which is more convenient in a problem with Low Reynolds where there are large variations of thickness of the boundary layer. And if there is some difference in the conception an generation of the mesh when I consider one or other alternative.

Thank you in advance!

The concept of scaleable wall function is coming from Menter. It is a scheme to ensure that there's no encroachment of the mesh in the log law region when you are using a law of the wall.

Thanks for your response Herve

I have more questions… If I am right when I use RSM I compute the Boundary Layer with the nodes that I put into its, and my first node have to be at a Y+ =2 approximately. Law of the wall in what region is applied? Y+ change in different places of the wall because thickness of boundary layer change and first node of the mesh respect of the wall is in different Y+ depending of the place. Scalable Wall takes into account this? Where I can find more information about Menter model?

Thank you very much again

Hi,

I think the purpose of the scalable wall function is that it allows you to be "careless" about your choice of y+ (y*). The edge of the viscous sublayer is assumed to be at the wall. If you contact CFX, they will send you a paper regaring the scalable wall functions. I am sure. Also, my definition of a scalable wall function is that used in NUMECA's software, not CFX's.

Hi J. Keays,

Thank you very much for your contribution. I don't understand very well when you say "The edge of the viscous sublayer is assumed to be at the wall" Do you mean that the limit between the boundary layer and principal flow is on the wall? Which is the thickness of the boundary layer?

Thank you again!

Martín

Martin, Contact your CFX vendor. He will send you the detailed paper of Menter who deviced the scalable wall function technique I believe and also happens to work for CFX.