Federico Alzamora Previtali

Hello Saif, 

how is the propeller moving? Are you setting a Dynamic Mesh with 6-DOF for the propeller to react to the incoming fluid? If you do, you have the option of Writing Motion History when setting it up.

You may also monitor the position of a point on one of the blades on your propeller. Choose an axis normal to your rotation vector and you should get a sinusoidal position as a function of time. The period of this sinusoid will be the inverse of your frequency.

I hope this helps!