Equation in Turbulent Intensity

gbgracio · July 8, 2023, 12:42

What is the equation used to determine the Turbulent Intensity in the fluent solution software?

LuckyTran · July 8, 2023, 14:16

The square of the (temporal) standard deviation of the mean velocity is zero because it is a mean. Clearly this is not what you mean...

However, there is the caveat that you cannot get the fluctuations, which if you remember is why we have turbulence models in the first place. So, the rmse of the fluctuations is back-calculated from $\sqrt{\frac{2}{3}k}$

Next is the issue is which mean velocity to use. You can take either the local mean velocity or a bulk average velocity or free stream velocity. For conventional reasons, most people use one of the latter ones. So... Fluent normalizes by the reference velocity in reference values which is a user specified number and default is 1.

If you want to calculate a turbulence intensity using local mean velocity, you have to create your own field function.

View Poll Results: What is the equation used in turbulent intensity?
The square of the standart deviation of the mean velocity divided by the mean velocity itself?	1	50.00%
Or another equation?	1	50.00%
Multiple Choice Poll. Voters: 2. You may not vote on this poll

July 8, 2023, 12:42	Equation in Turbulent Intensity	#1
gbgracio New Member Guilherme Grácio Join Date: Jul 2023 Posts: 1 Rep Power: 0	What is the equation used to determine the Turbulent Intensity in the fluent solution software?

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July 8, 2023, 14:16		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,747 Rep Power: 66	The square of the (temporal) standard deviation of the mean velocity is zero because it is a mean. Clearly this is not what you mean... However, there is the caveat that you cannot get the fluctuations, which if you remember is why we have turbulence models in the first place. So, the rmse of the fluctuations is back-calculated from $\sqrt{\frac{2}{3}k}$ Next is the issue is which mean velocity to use. You can take either the local mean velocity or a bulk average velocity or free stream velocity. For conventional reasons, most people use one of the latter ones. So... Fluent normalizes by the reference velocity in reference values which is a user specified number and default is 1. If you want to calculate a turbulence intensity using local mean velocity, you have to create your own field function.