Learning Forum

[Alek Nino]

I would like to know the equations that relate mean and RMS velocity components. I have found some other posts that relate the variables but are pretty old and wanted to confirm ANSYS's relation specifically. If someone could share the relations or a link to ANSYS documentation that would be great. 

The specific names of the variables in CFD Post in question are:

Mean X Velocity, Mean Y Velocity, Mean Z Velocity

RMS X Velocity, RMS Y Velocity, RMS Z Velocity

Velocity u, Velocity v, Velocity w

My goal is to use these variables to calculate the turbulent kinetic energy and turbulent intensity and I also want to confirm that I am using the right variables to display my velocity contours. 

Thanks in advance!

[Federico Alzamora Previtali]

Hello Alek, 

Velocity [u,v,w] is the instantaneous resolved velocity -> Ui;

Mean Velocity [u,v,w] is the time averaged resolved velocity -> {Ui}^bar

RSME Velocity [u,v,w] is the fluctuating velocity -> Ui'

where 

Ui = {Ui}^bar + Ui'

 

[Alek Nino]

Thank you for your response, but is the RMS velocity the same as RMSE or do I need an additional expression to obtain RMSE. A previous post that answered this question wasn't very clear to me so some clarification would be great. From what I understand, if they are different, then is Ui' = SQRT(U_RMS^2), where Ui' is the RMSE velocity.