A unique, actively controlled pumping system allows independent control of inflow and impeller perturbations, as well as the phase shift between them. The basic configurations of an impeller and an impeller-diffuser blade system have been investigated, with the objective of manipulating the spectral content of the unsteadiness of the near-wake at the impeller discharge. Substantial alteration of the discrete spectral components can be attained. A central feature is the generation of a number of nonlinear interaction components, corresponding to sum and difference frequencies, of the forcing- and blade passing-frequencies and their harmonics. With proper choice of perturbation conditions, it is possible to attenuate the inflow perturbation, as well as to alter the magnitudes of the blade passing component and its harmonics.

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