Hydraulic Diameter
 

I'm trying to solve a sudden expansion mesh in FLUENT using K-e model. I'm using turbulent intensity and hydraulic diameter for giving turbulence BC. I want to what should be the hydraulic diameter for a axisymmetric sudden expansion and also how do I guess the value of turbulence intensity?

CFD-Wiki contains an estimation of the turbulence intensity in a fully developed pipe flow. see http://www.cfd-online.com/Wiki/Turbulence_intensity. That page also links to the definition of the hydraulic diameter.

For a sudden expansion there are two diameters. which one should be taken into account when I'm interested only the flow behaviour at the downstream of the expansion.

can you please help me setting the BC for a sudden expansion?? I really need some help here.

What you want to compute are boundary conditions at the inlet, right? Then it is the inlet dimensions that you should use.

yes. BC at inlet.

so simple!

n eureka ! i just discovered that .. any response < 10 characters won't get submitted to the forum.

P.S: was it to stop spam ?

I'm posting the pics of sudden expansion. The inlet dimensions were variable in the actual experiment but How do I do that in the given mesh? I have to compare the results with the experimental data.