I am comparing a couple manifolds made in different ways - (1) cast manifold (2) fabricated manifold. Cast manifold surface is much more rough than fabricated. Is there a way to input surface condition into Fluent to highlight the difference. I am doing a steady state flow - k-epsilon turbulent

Thanks venu

Hi,

To incorporate the effects of surface roughness you need to specify a couple of values - 'Surface roughness' and 'roughness constant'. These are accessed through the boundary condition panel for the surface and under the momentum tab. The surface roughness value is defined as a physical measure of the roughness of the surface, think of it as a measure of the height of each individual irregularity on the surface. A common example is a surface covered in sand grains, in this case the roughness height would be the height of the sand grain. If you specify it as 0 then the surface will be treated as completely smooth. To get the surface roughness your best bet is to do some internet searches, you may not find the exact material but you should find something similar.

The roughness constant default value is 0.5 which has been demonstrated to represent uniformly rough surfaces well - castings are generally quite uniformly rough so you can probably leave this value as it is. Non uniformly rough surfaces require a different value, normally higher.

Hope this helps

Steve

Thanks a lot! Steve, I will dig into that. Should we assume no shear condition for rough and smooth cases with the difference being in height and coefficient?

Venu

You should set the walls for both cases as 'no slip' (no specified shear).

Steve