[lxlylzl]

I want to compute the frequency of rotating fluid in a cylinder whose rotational axis does not coincide with the geometrical axis of cylinder. In fact, the axis of rotating fluid, indeed, revolves around the geometrical axis.

For my problem I recorded velocity time series at a point lying on the geometrical axis and carried out the FFT. I have two distinct peaks, which means I have two periodicity in the system. One peak is known to me as the rotation (precession) of the axis of rotating fluid about the geometrical axis.

I am confused about the other peak. Since the velocity time series is recorded at the geometrical center, will it account for the frequency of fluid rotating about its own axis? What I mean is that w.r.t. the geometrical axis, the rotation of fluid about its own axis will be in non-inertial frame of reference.

I am confused......., Plz help....