# Turbulence Intensity

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 March 19, 2016, 10:32 Turbulence Intensity #1 New Member   Niels Hawinkel Join Date: Mar 2016 Posts: 6 Rep Power: 3 I'm trying to model the drag coefficient on a car. When i set the Turbulence Intensity to 15% at the inlet and outlet backflow and plot the result, I can see that the turbulence intensity immediatly drops to basically 0% right after the inlet (so it has no influence). The turbulence viscosity ratio is 10 and I use a uniform velocity profile (25m/s horizontal at inlet). How do I solve this?

 March 20, 2016, 12:59 #2 New Member   Niels Hawinkel Join Date: Mar 2016 Posts: 6 Rep Power: 3 up, post boost

 March 24, 2016, 06:04 #3 New Member   Niels Hawinkel Join Date: Mar 2016 Posts: 6 Rep Power: 3 up, post boost

 March 25, 2016, 14:21 #4 Senior Member   Lucky Tran Join Date: Apr 2011 Location: Orlando, FL USA Posts: 1,904 Rep Power: 26 A uniform velocity profile is shear free and therefore has limited capability to produce and sustain turbulence. Thus any turbulence at the inlet will eventually decay and die out (reach 0%). The question is how long of a distance until it decays and this depends on the length scale of the turbulence. A turbulence viscosity ratio of 10 is extremely (pathetically) mild. This magnitude of the viscosity ratio is what you would expect to see at the edge of a boundary layer (the freestream boundary, where the shear is very small and very little turbulence exists).

February 3, 2017, 15:24
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Quote:
 Originally Posted by NielsHaw I'm trying to model the drag coefficient on a car. When i set the Turbulence Intensity to 15% at the inlet and outlet backflow and plot the result, I can see that the turbulence intensity immediatly drops to basically 0% right after the inlet (so it has no influence). The turbulence viscosity ratio is 10 and I use a uniform velocity profile (25m/s horizontal at inlet). How do I solve this?
Hi NielsHaw,

Did you find the way to solve this problem? I'm getting the same results when running a 16% turbulence intensity external flow case.

Thanks,

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