Numerical Investigation Of Cavitation Flow Induced Noise

With the continuous development of hydraulic machineries to high power,high speed,and high loadings,the problems of noise induced by cavitation flow are increasingly outstanding,which become the core and key technical problems that related to the target stealth and combat performance of underwater weapons,water surface and underwater vehicles.The mechanism research on cavitation flow induced noise has always been a frontier issue in the research field of hydraulic machineries due to its complexity and seriousness of damages,meanwhile,it is further the premise and foundation to put forward reasonable noise reduction measures.This paper first reviews the numerical research status of cavitation flow and its induced noise at home and abroad to establish the calculation method of cavitation flow and its induced noise,and then the theoretical basis and mathematical models of numerical prediction involved in the paper are introduced.Based on different mechanism of cavitation flow induced noise of the underwater target,the main components of the noise are divided into loading noise and bubble noise.The hybrid method in the frequency domain based on the theory of acoustic analogy is used for the prediction of loading noise,while a time domain method based on the theory of spherical bubble acoustic radiation is adopted to predict bubble noise.The basic research on cavitation flow induced noise of an Clark-Y hydrofoil model is firstly carried out,and the results indicate that: non-cavitation loading noise is mainly subjected to linear spectrum property at the low frequency,and the acoustic fundamental frequency is basically the same with the frequency of vortex shedding,which means that the radiation noise is mainly modulated by periodic shedding of vortex structure on the trailing edge.In the stage of sheet/cloud cavitation,the continuous spectrums of loading noise is significantly enhanced compared to the linear compositions.meanwhile,the bubble noise becomes the main noise source that radiates broad spectrums,and the radiation noise is mainly modulated by the periodic shedding of attached sheet cavitation on the leading edge.In the cloud cavitation stage,the loading noise is similar to that of sheet/cloud cavitation in the transitional stage,while the bubble noise's first and second peak frequency of the acoustic power spectrum density,respectively,is consistent with the shedding frequency of cloud cavitation on the leading edge and the shedding frequency of vortex structure on the trailing edge.Nevertheless,it is worth to notice that the acoustic power density of bubble noise is concentrated in the higher frequency bands,which may be resulted from the growth and shedding behavior of multiple-scale bubbles behind the tail of cavity.Combining with the engineering practice,take the high skewed propeller of full-scale as research object to explore the intrinsic relationships between the propeller sheet cavitation flow and its radiation noise.The results show that: The acoustic energy of propeller loading noise is concentrated at the low frequency and the radiation noise is mainly subjected to linear spectrum property at its low-order blade passage frequency,exhibiting a distinct dipole characteristics,in the stage of both non-cavitation and cavitation.In the non-cavitation stage,the maximum sound pressure level occurs at the first order of blade passage frequency,and the sound pressure level from low-order to high-order is followed by a decreasing trend.While in the stage of propeller sheet cavitation,though the maximum sound pressure level of loading noise is still in the first order of blade passage frequency,the sound pressure level of its low-order blade passage frequencies become more complicated.Also in this stage,the bubble noise becomes the main source,whose acoustic energy is concentrated at the low frequency and the radiation spectrum is broadband characteristics,and the maximum sound pressure level of bubble noise is at the first order of blade passage frequency.Weather it is loading noise or bubble noise,the radiation noise spectrum can reflect its relationships with the geometric feature of the propeller and the operating condition,which provides a reference for the selection of propeller noise reduction measures and the design of low noise propeller.