Research On The Characteristics And Control Technology Of Unsteady Cavitation Flow Around Hydrofoils

Cavitation is a complex flow phenomenon that occurs uniquely in liquids.It involves the process of steam or gas bubbles forming,developing,shedding,and collapsing in the liquid or on the liquid-solid interface when the local pressure in the liquid drops to the saturated vapor pressure.The occurrence of cavitation can cause strong nonlinear flow,which in turn affects the safe and stable operation of machinery.Additionally,cavitation can increase hydraulic machinery resistance,affect its hydrodynamic performance,and reduce work efficiency.The energy and pulse generated during cavitation are extremely destructive,causing erosion of machine surface material,cavitation,and strong cavitation noise.A systematic investigation was conducted in this paper on the unsteady cavitation characteristics of hydrofoils.The generation mechanism and control mechanism of cavitation were explored,and a solution was proposed to effectively control cavitation by combining active jet and passive control technology.The effectiveness of cavitation suppression was comprehensively evaluated based on the hydrodynamic performance and noise of the cavitation flow field.The main research contents are as follows:(1)The detached eddy simulation(DES)method and the Schnerr-Sauer cavitation model were used to analyze the unsteady cavitation flow characteristics around the hydrofoil and the mechanism of cavitation,and the cavitation flow field noise was numerically predicted in combination with the permeable FW-H acoustic analogy equation.Considering the installation error between the hydrofoil and the wall in the experiment,this paper discusses the influence of the existence of the gap on the cavitation flow characteristics.The research results show that the cavitation generated in the gap accelerates the shedding of the cavitation cloud on the suction surface of the hydrofoil.The cavitation bubbles generated at the location will excite additional noise,resulting in an increase of the total sound pressure level of the cavitation far-field noise by 4～5d B.(2)Based on the idea of blocking and weakening the backflow to control cavitation flow,a jet groove structure is proposed near the separation point of hydrofoil flow and active jet flow is carried out.The results show that the active jet mode can effectively restrain the length of cavitation generation and development at the leading edge of the hydrofoil,and the shedding and collapse of small-scale vortices will occur in the downstream of the jet groove,avoiding the instability of hydrodynamic performance caused by the shedding of large-scale vortices;The active jet mode can effectively reduce the far-field noise of hydrofoil cavitation,and considering the hydrodynamic performance and the noise result of cavitation flow field,the active jet with zigzag jet groove structure has a more obvious inhibition effect on cavitation.(3)The characteristics of cavitation flow field and the noise of cavitation flow field of propeller are numerically calculated by hybrid computational hydro-acoustic.The results show that with the increase of the advance coefficient,the propeller thrust and torque decrease,the open water efficiency increases first and then decreases,and the cavitation hydrodynamic performance of the propeller gradually approaches to the hydrodynamic performance without cavitation.With the increase of the cavitation number,the cavitation degree gradually weakens.The cavitation noise of propeller presents obvious quadruple noise characteristics.