Turbulence Intensity

NielsHaw · March 19, 2016, 09:32

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?

NielsHaw · March 20, 2016, 11:59

up, post boost

NielsHaw · March 24, 2016, 05:04

up, post boost

LuckyTran · March 25, 2016, 13:21

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).

Piedrapablo · February 3, 2017, 14:24

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,

March 19, 2016, 09:32	Turbulence Intensity	#1
NielsHaw New Member Niels Hawinkel Join Date: Mar 2016 Posts: 6 Rep Power: 10	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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March 20, 2016, 11:59		#2
NielsHaw New Member Niels Hawinkel Join Date: Mar 2016 Posts: 6 Rep Power: 10	up, post boost

March 24, 2016, 05:04		#3
NielsHaw New Member Niels Hawinkel Join Date: Mar 2016 Posts: 6 Rep Power: 10	up, post boost

March 25, 2016, 13:21		#4
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,674 Rep Power: 65	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).