A theoretical investigation of hydraulic noise in pumps

Abstract

A theoretical investigation of hydraulic noise produced by volute and diffuser pumps was carried out to determine the effect of design and operating conditions on the noise level in the pumped liquid. Preliminary theoretical work showed that the noise measured by hydrophones in the pump discharge branch was related to the static pressure fluctuations across the exit from the pump volute and a theory based on the potential flow analysis of fluctuating flow through series of blade cascades, in which viscous wake effects were included, produced expressions enabling the effects of pump load, cutwater position and pump speed on the noise level of the pump, to be estimated. This theory showed that although noise generated by the pump casing itself was unimportant, blade circulation and blade wake were of prime importance in determining the pump noise level and the interaction between these two was responsible for the effect of pump loading. The theory also provided an explanation of the observed interaction between the blade frequency noise and the shaft frequency noise if it was also assumed that the impeller flow pattern was asymmetrical. The above theory was compared with some experimental data taken on two pumps, and the effects of pump speed, cutwater clearance and pump load showed satisfactory agreement, particularly since no adjustable parameters were involved. In addition, a simple empirical formula, based on a wider range of pumps, was produced, enabling the general noise level measured in the discharge branch of a pump to be predicted to within ± 2 dB for pumps of a wide range of specific speeds and power consumption groups.