hello user, i want to know that how we can capture the boundarly layer in CFX5.5 and we should use the wall function or not and for boundary layer capturing whcih tubulence model should be used for incompressible flow. Thanks in advance

You got to create an inflated mesh that adequately resolves the boundary layer, which means you'll have to have an idea of the BL thickness. Go search for "modelling flow near the wall" in the manual for the details. I got good results with y+ of the first node point close to 11, but some people suggest going as low as 2.

Wall functions depend on the turbulence model you're going to use, k-e based models use them, k-w based not. Turbulence model depend on your application, but for general incompressible flow in favourable pressure gradient normal k-e should be fine. Use scalable wall function in konjunction with k-e, unless you know the standard ones give better results. You can also use the SST model and compare the results.