# Turbulent parameters for external flow

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 June 28, 2017, 01:33 Turbulent parameters for external flow #1 New Member   Join Date: May 2017 Location: Japan, Kitakyushu Posts: 19 Rep Power: 5 Hello, I'm trying to set up a k-omegaSST model but I'm facing some problems to determine the value of the parameters. I want to simulate a supersonic external flow around a rocket body. The more I seek the answer, the more questions I have. For k, I need the turbulent intensity however I've just found some relations for internal flows using characteristic length as diameter of a pipe. But nothing precise for an external flow. According to this discussion : Turbulence length scale and intensity The turbulent intensity should be around 0.07-0.01%. But this result is based on an exp(N) criterion. I can't find any explanation about this, do you know some paper which explains this ? I thought the value of k at the inlet depends only of the inlet flow and not the geometry but if I well understood the exp(N) criterion is related to the shape of the solid. I'm a bit lost... To find omega I started to search the mixing length, but once again I didn't find any relation for an external flow. So, I've decided to use the velocity ratio thinking it would be easier to find a value. I often see that for a wind tunnel the value is around 1-10. How can I decide to use 1 more than 10, or the opposite ? I used the cfd-online calculator with a freestream velocity equal to 1208 m/s (Mach 3, gamma=1.35) : https://www.cfd-online.com/Tools/turbulence.php But according to the value of Tu (0.01-0.07) and viscosity ratio (1-10) the results range from 71500 to 145 s-1 for omega and from 0.00001 to 0.001 m for the turbulence length scale. Thank you for your help !

 Tags parameters, turbulent