Unsteady cavitation analysis of the centrifugal pump based on entropy production and pressure fluctuation

Authors

Qiaorui SI - Jiangsu University, China, People's Republic of China
Fanjie Deng* - Jiangsu University, China, People's Republic of China
Yu Lu - Jiangsu University, China, People's Republic of China
Minquan Liao - Jiangsu University, China, People's Republic of China
Shouqui Yuan - Jiangsu University, China, People's Republic of China

Abstract

After cavitation occurs, the flow structure inside the centrifugal pump is complex, and the volume pulsation and collapse of the cavity will radiate large noise, which seriously affects the concealment and comfort of the pump system equipment. a numerical simulation method of cavitation induced noise is proposed based on acoustic finite element method and spherical cavity radiation theory. And cavitation induced noise of NACA0015 hydrofoil is simulated numerically based on the study of unsteady cavitation flow around hydrofoil. Furthermore, considering the effect of impeller rotation, a RZGB cavitation model is obtained based on the secondary development technology. Combined with numerical simulation and experimental measurement, the unsteady cavitation flow and induced noise characteristics of a medium specific model pump is studied.Combined with the numerical simulation method and experimental measurement, the cavitation induced noise at the inlet of the model pump was studied, and the internal relationship between the unsteady cavitation flow and cavitation induced noise was analyzed and discussed. The results show that: the sound power value of the suction surface of the model pump blade is larger than that of the pressure surface of the blade. With the decreases of the cavitation number, the area covered by cavitation on blade suction surface gradually increases, and the acoustic power value will also increase. The cavitation volume fluctuation is the main reason for the increase of acoustic power. Under different cavitation numbers, the sound energy of cavitation induced noise of the model pump is mainly concentrated in the low frequency band of 0~2StBPF, and the main frequency of SPL is the blade frequency and its multiple frequency, indicating that the cavitation induced noise of the model pump without considering the cavitation volume pulsation is modulated by blade sweep. The frequency corresponding to the peak value of the SPL of the cavity volume pulsating radiated noise is the cavity shedding frequency, indicating that the cavity volume pulsating radiated noise of the model pump is modulated by the cavity shedding. With the decrease of cavitation number, when the cavitation of the model pump reaches the serious stage, the sound pressure and pressure level at the inlet of the model pump presents a decreasing trend, indicating that with the development of cavitation, the cloud cavitation in the impeller low pressure area will absorb the radiated noise generated by the collapsing cavitation in the downstream high pressure area. Secondly, a large number of cavitation may gather at the inlet of the impeller to cause blockage, and the incoming flow in the inlet pipe interacts with the cavitation to form an impact, which causes the cavitation to move downstream, thus affecting the upstream propagation of sound waves.