Experimental study of cavitation noise characteristics in a centrifugal pump based on power spectral density and wavelet transform

Cavitation is a harmful flow pattern in hydraulic machinery that disrupts the normal energy exchange and damages the flow channel components. Therefore, studying cavitation in hydraulic machinery and exploring efficient monitoring methods are currently key research topics. This paper examines the characteristics of inlet and outlet noise from centrifugal pumps at different stages of cavitation development under multiple flow rates. The results indicate that: The inlet and outlet noise of a centrifugal pump mainly consists of discrete noise and broadband noise. Discrete noise is shaft passage frequency, blade passage frequency, and their lower harmonic frequencies. The energy is mainly concentrated in discrete noise. Cavitation has a significant impact on the noise at the inlet, where the power spectral density of discrete noise and broadband noise both sharply decrease as cavitation develops, while the noise at the outlet is largely stable. Through relative energy analysis, it has been found that the relative energy of the different layers of noise at the inlet and outlet changes a lot as cavitation happens. The obvious wavelet energy fluctuation layer of inlet noise is relatively wide, while the obvious wavelet energy fluctuation layer of outlet noise is relatively concentrated, especially in the frequency-containing layer. The wavelet time-frequency diagram indicates that the cavitation noise of centrifugal pumps exhibits temporal stability and is devoid of stochastic interference. It can be observed that the sudden change in sound field during centrifugal pump cavitation is a significant characteristic, and earlier detection of cavitation occurrence can be achieved by analyzing the power spectral density of noise at both inlet and outlet of the pump as well as monitoring relative energy changes in wavelet decomposition layers.