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Equation in Turbulent Intensity

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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

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Old   July 8, 2023, 11:42
Question Equation in Turbulent Intensity
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Guilherme Grácio
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What is the equation used to determine the Turbulent Intensity in the fluent solution software?
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Old   July 8, 2023, 13:16
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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.
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