hello, I found in many tutorials of fluent6.0(like elbow tutorial), in specifying turbulence boundary conditions that turbulence is modeled with INTENSITY % and hydraulic diameter the values of I% (often 10%)do not correspond with the definition of I%=(Rdh)^(-1/8) (etablished in user guide, modelling turbulence). and what exactly the hydraulic diameter. thanks

Ok, good question.

Turbulence intensity calculation procedure as outlined in the Fluent manual works well for internal duct flows. Usually for such flows, using 1 or 10 percent makes little difference as eventually, the value changes as the solution proceeds due to the viscous effects that result due to the presence of the wall.

This page provides a good explanation about the Hydraulic Diameter:

http://www.piping-toolbox.com/hydrau...er-18_458.html

ok PU1! how about the Reynolds number presented in the first part of the tutorial ( Re=50000)!! and the formula I%=f(Re)??

thanks for all

I'm not sure what exactly you are referring to, but even for a pipe elbow case, using 1 OR 5 or even 10% Turbulence Intensity should not influence the results for the same reason as I have given earlier in this thread.