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Old   March 19, 2016, 10:32
Default Turbulence Intensity
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Niels Hawinkel
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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?
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Old   March 20, 2016, 12:59
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Old   March 24, 2016, 06:04
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Old   March 25, 2016, 14:21
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Lucky Tran
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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).
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