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In this paper, the TVDFT Order Tracking technique (Time Variant Discrete Fourier Transform) is used to process complex non-stationary signals, generated by real measured signals. The method is applied in an experimental set-up for several run-ups, in order to identify the forward and backward precession movement in the directional order map. In this map, the negative orders are related to the backward and the positive ones to the forward orbit movement. The directional order maps are obtained for several rotor stations in order to identify the mixed operational modes, i.e., when some stations of the rotor describe their precessional movement in the forward direction while others move in the backward direction simultaneously. The experimental results showed the influence of the spatial distribution of the imbalance in the occurrence of the mixed operational modes.

The quality of the results of any order analysis depends on the accuracy of the tachometer signal used to estimate the instantaneous rotational speed. There are several techniques used to process the tachometer signal. However, in some cases, there are difficulties in measuring this signal due to physical limitations of the equipment under analysis. This paper investigates a methodology to estimate the instantaneous frequency of a nonstationary signal using the Directional Wigner Distribution. Therefore, the variation of the rotational speed of a rotating equipment can be obtained using only the accelerometer signal, eliminating the need of acquiring the tachometer signal.