An experimental investigation is presented which analyzes the fluctuating pressure field existing in the volute of a centrifugal pump, in order to characterize the effects of blade-tongue interaction. For that purpose, pressure signals were obtained simultaneously at different locations on the volute casing and for different flow-rates by means of fast-response pressure transducers. Particular attention was paid to the pressure fluctuations at the blade passage frequency, regarding both amplitude and phase delay relative to the motion of the blades. The dependence of the obtained pressure fluctuations with respect to both flow-rate and position along the volute clearly indicates the leading role played by the tongue in the impeller-volute interaction and the strong increase of the magnitude of the dynamic forces in off-design conditions.
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