Learning Forum

[mutianzi1]

Hello!

 

I was working on CFD simulations of a wind tunnel testing. I used Large Eddy Simulation (LES) as the Viscous Model. At the Velocity Inlet, I used a UDF for the X-velocity, which follows the power law. Y- and Z-velocity are zero. For the input regarding turbulence. I selected Spectral Synthesizer for Fluctuating Velocity Algorithm. I used Intensity and Length Scale for the Specification Method. Turbulence Intensity is 10%, and Turbulent Length Scale is 0.01 m.

 

After the calculation is completed. I would like to plot the contour of turbulence intensity for the computational domain, but I cannot find turbulence intensity from the drop down list. I only found Subgrid Turbulent Viscosity, subgrid Effective Viscosity, subgrid Turbulent Viscosity Ratio and subgrid Filter length.

 

I also tried Custom Field Function, but turbulence intensity is calculated based on turbulence kinetic energy and mean velocity. Turbulence kinetic energy is also not available in the outputs.

 

I am wondering whether you can give me some suggestions on how to plot turbulence intensity contour when LES turbulence model is used.

 

Another question is that will turbulence intensity decay with the distance from the velocity inlet? If it decays with distance, how can I evaluate the turbulence intensity at the inlet to make sure turbulence intensity of the location of interest will reach the expected value?

 

Any help are greatly appreciated.

 

Best Regards!

[Keyur Kanade]

its not directly available for les. 

you can create a custom field for it using following. 

if this helps you, please mark this post as 'is solution' to help others on forum. 

[mutianzi1]

Hello kkanade,

 

Thank you very much for your reply and for providing the equation to calculate turbulence intensity.

 

I have one more question about the equation. For the turbulent velocity fluctuations, they are also not directly available, right? This one might be easy to define in the custom field by subtracting the mean from the time history of the velocity. But how can I define the mean of the square of the turbulent velocity fluctuations in the custom field in Fluent? I did not find where to define the mean value in the Custom Field Function Calculator. Could you please give me some suggestions on this? 

 

Best Regards!

 

 

 

 

 

 

[DrAmine]

You need to enable transient data sampling to get access to mean values

[mutianzi1]

Hello Amine,

 

Thank you for your suggestion! Can I also get root-mean-square of velocity fluctuations by enabling data sampling?

 

Best Regards!

[Rob]

I think so: switch it on and have a look! 

[DrAmine]

Yes.

[mutianzi1]

Thank you!

[mutianzi1]

Thank you!