Hi all....

I have doubt about definition of turbulence intensity when I try to compare CFD turbulence profile with my experiment.

TI= u'_RMS(x)/U_mean(x)

Should I take absolute value of U_mean(x) while calculating U_mean(x)? CFD shows reverse flow (negative velocity) at some locations.

Thanks for help.

Turbulence inensity is always positive.

You should take the absolute value of the mean flow velocity. Check out the CFD-Wiki page on turbulence intensity for a more comprehensive definition. You can find it here:

http://www.cfd-online.com/Wiki/Turbulence_intensity

Jonas is correct, but I rather say (like in the Wiki information that Jonas added recently) that you should take the speed or norm of the transient averaged velocity vector, i.e. U .

Absolute value of a vector is a generalization and may confuse those not used to it.. I rather say the norm of the velocity vector or speed.

good luck, Opaque.