Noise as indicator of instability in centrifugal pumps

Abstract

The total emitted noise from the pumping set is generated partially by the pump, partially by the electric motor and partially by the cooling fan, and has four characteristic noise origins: aerodynamic, hydrodynamic, mechanical, and electromagnetic. Emitted noise level of a centrifugal pump depends on its size and the operating conditions (speed and load). At the design point of operation (Qdes) and without cavitation the hydrodynamical and aerodynamical noise in form of the rotational noise due to the rotational frequency and blade passing frequency are predominant noise sources. At the off-design operating condition the dominant noise sources within the pumping set without cavitation of the pump is nonrotational noise due to the rotating stall and surge, at Q<Qdes, and due to the laminar boundary layer vortex shedding, at Q>Qdes. When the cavitation within the pump occurs the nonrotational noise predominates within the entire range of operating conditions. The onset of the stall, surge, and cavitation in the centrifugal pump cause instability of a pumping system. Special attention was given to the state of pump operation when the instability due to the stall or surge and cavitation simultaneously occurs, and to the noise generated thereof.