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Is negative turbulence intensity right?

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Old   April 18, 2006, 10:00
Default Is negative turbulence intensity right?
  #1
Oliveir
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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.
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Old   April 18, 2006, 10:35
Default Re: Is negative turbulence intensity right?
  #2
Jonas Larsson
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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

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Old   April 18, 2006, 12:33
Default Re: Is negative turbulence intensity right?
  #3
opaque
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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.

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