This Review describes the research work conducted by many researchers in the field of hydro-acoustics of centrifugal pumps. This study aims to understand the flow induced noise mechanism, factors affecting it, and available methods to attenuate the same in centrifugal pumps. In general, the noise generated by a pump is interpreted in terms of pressure pulsations and can be represented in the frequency domain as a combination of discrete components and broadband components. In the discrete frequency noise component, the major emphasis is given on blade pass frequency noise and its relation to the rotor–stator interaction in pumps. The intensified rotor–stator interaction results in high pressure pulsations, thus strong flow induced noise. The effect of various geometrical parameters on the rotor–stator interaction and available methods to mitigate it to reduce noise are discussed in detail. Apart from the rotor–stator interaction, the importance of energy loss mechanisms, such as flow recirculation, flow-separation, and jet-wakes occurrence in pumps, which affect the blade pass frequency component, are also discussed. One of the other discrete noise components, the rotating stall mechanism with its physical mechanism, was also explored in detail. Subsequently, two major phenomena of broadband noise components, turbulence and cavitation, are explained. For cavitation, the phenomenon is elaborated in detail as well as various methods explored by the researchers to predict the existence of the cavitation phenomenon using the acoustic spectrum. Conclusions are also drawn for each source by describing the major events. In the end, the possible future scope of work that can be explored is given.

Various geometrical parameters like cut-water clearance, volute tongue location, tongue radius, vane trailing edge profile and flow parameters like speed, operating point affect the rotor-stator interaction in a centrifugal pump. In the present investigation, vane trailing edge is selected as a design parameter for profile modifications to study and reduce the rotor-stator interaction intensity and hence the pressure pulsations. A double suction centrifugal pump with tangential discharge volute (M1), specific speed (n_s) 19 has been selected for the numerical experiments. Transient analysis using Detached Eddy Simulation is used for predicting flow parameters behavior at impeller periphery (primary source) and volute tongue locations (secondary source). The impeller periphery probes in the rotor-stator interaction zone are used to identify the intensity of jet-wake flow phenomenon and its interaction with the volute tongue. Similar strategy has been applied by modifying the trailing edge profile of the original geometry with vane underfiling (M2) and the M2 vane geometry with novel trailing edge profile (M3). The pressure pulsation behavior along the impeller periphery (primary source) shows the strong reduction of pressure amplitude near volute tongue by 42% in M3 compared to M1 aligning with the reduction of jet-wake flow intensity. The pressure fluctuation (rms) near volute tongue (secondary source) shows an average reduction of 11% in modified trailing edge (M3) relative to M1. The intensified rotor-stator interaction due to vortex shedding in M2 causes relatively higher pressure fluctuations (rms) near volute tongue compared to M1 and M3.

A numerical investigation was performed to study the wake dynamics of a D-shaped cylinder, and the effect of the aspect ratio of the cylinder on the onset of primary instabilities was explored. The aspect ratio ( L/D) is varied by increasing the cylinder’s length ( L) while keeping the cylinder’s diameter ( D) constant. Five aspect ratios ranging from 1 to 3 in increments of 0.5 were considered for the present study. The essential variables are the Reynolds number (Re) and the aspect ratio (AR). The primary instability analysis was performed using the Stuart-Landau equation to determine the critical Reynolds number value where the instability sets in. At low Reynolds number, the flow is steady and symmetric; at critical Reynolds number, the flow experiences Hopf bifurcation resulting in a time-periodic flow. As the aspect ratio was increased, the critical Reynolds number over which the primary instability sets in was found to increase linearly in the present study. Increasing the aspect ratio leads to significant modification of the flow topology and force coefficients. For aspect ratio two, the wake is more streamlined and narrower leading to a drag reduction of 14.49%. The drag reduction magnitude diminishes with a further increase in aspect ratio due to increased surface area resulting in more friction drag. The phase diagram and Fast Fourier transform (FFT) analysis revealed a reduction in vortex shedding activity, and velocity fluctuations in the wake.