A general theory is proposed for the small disturbance field in strongly swirling flows in turbomachines. In contrast to the situation in nonswirling flows, vorticity, pressure, and entropy fields are not independent. Shear disturbances are not purely convected but rather propagate slowly in flows stable in the sense of Rayleigh, and are unstable in flows approaching free vortices. In the course of the propagation, there is an interchange between radial and tangential velocity perturbations. General conditions for propagation of pressure modes in the strongly swirling flow show the effects of rotation to be small if the frequency is large compared to base rotational frequency. Oscillatory shear flows have been observed in experiments in the MIT Blowdown Compressor.
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Jack L. Kerrebrock (1977) studied this question.