Cyclostationarity by examples

Cyclostationary modelling of rotating machine vibration signals

Cyclostationarity in rotating machine vibrations

The unsteady flow field generated by the rotor provides unsteady aerodynamic excitations to the downstream stator, which can result in vibrations such as forced response In this paper, measurements of the rotor wake and rotor tip leakage flow from an embedded rotor in a multistage axial compressor are presented A unique feature of this work is the pitchwise traverse of the flow field used to highlight the changes in the rotor exit flow field with respect to the position of the surrounding vane rows Results acquired at mid-span focus on characterizing an average rotor wake, including the effects on the frequency spectrum, from a forced response perspective While many analyses use an average rotor wake to characterize the aerodynamic forcing function to the downstream stator, this study explores the factors that influence changes in the rotor wake shape and the resulting impact on the spectrum Additionally, this paper investigates the flow near the endwall where the tip leakage vortex is an important contributor to the aerodynamic excitations for the downstream vane For the first time, experimental data are presented at the rotor exit, which show the modulation in size and radial penetration of the tip leakage vortex as the rotor passes through the upstream vane wake As computational models become more advanced, the ability to incorporate these aerodynamic excitation effects should be considered to provide better predictions for vane vibratory responseCopyright © 2015 by ASME

Considerations for Measuring Compressor Aerodynamic Excitations Including Rotor Wakes and Tip Leakage Flows

Fast-response pressure measurements collected in a three-stage axial compressor highlight the development of the rotor tip leakage flow. Data collected from an array of high-frequency-response pressure transducers measure time-resolved static pressure over the rotors at several loading conditions for three tip clearance heights. The influence of surrounding vane rows on the rotor tip leakage flow is investigated by adjusting the position of the vanes with respect to fixed sensor positions. One key result is that the wake from the upstream vane creates a modulation of the leakage flow. However, the upstream propagating potential field from the downstream vane row has no measureable impact on the leakage flow trajectory. In some cases, variations of the leakage flow trajectory angle due to these blade row interactions are greater than the differences due to a doubling of the rotor tip clearance height, an important finding not previously reported in the literature. Differences of the leakage flow trajectory...

M. Suarez

Papers

The stochastic structure of downstream pressure from an axial compressor—ii. an investigation of blade-to-blade variability

The stochastic structure of downstream pressure from an axial compressor—i. a periodic time–frequency spectral description