[nasir.iitd]

Hi Everybody,
I want to calculate integral length scale( axial and transverse), turbulent length scale and energy spectra of my cylindrical domain in fluent.Can anybody help me?

[Vandeley]

The integral length scale is quite easy to calculate (by two-point correlation), you will need at least 15 points in a line that preferably is located 1 cell distance from each other. You will need to sample the u-velocity for your points in axial direction and the same can be done for the two other velocity components. (i usually save a .csv file for every time step with the velocities for every point in the line/rake)
Now that you are sampling the data for each point you will need to sample for a number of flow through's for the domain to get a good correlation.

When you are done with the sampling you can write a Matlab script to store the velocities in each point over time by reading the .csv-files. Then just solve the equation:


For the integral length scale one usually says the signal correlates when B_uu < 0.2, so just sum the values until the signal decorrelates and multiply with the Delta x/y/z

[nasir.iitd]

Hello Vandeley,
I have the data and case files in .cas and .dat format. How to introduce 15 points to fluent for calculation? Is the Matlab script of the formula is to be wriiten as UDF before simulation starts or after the simulation completes? Are u'1,RMS and u'1 rms values?

nasiruddin