Study On The Effect Of Bionic Structure Of Sailfish Tail Fin On Cavitation Performance In Centrifugal Pump

Cavitation issue is inevitable in the operation of fluid machinery,the instability caused by cavitation will lead to drastic changes in the global flow rate and pressure,which will cause the dynamic characteristics of the unsteady rotor and eventually lead to the destruction of the hydraulic system structure.The low specific speed centrifugal pump has the characteristics of high lift,small flow rate and low efficiency,when the impeller inlet pressure drops to the saturation pressure,it is easy to cavitate at the back of the blade inlet.The generation of cavitation leads to increased unsteady turbulent pulsation inside the impeller,drastic changes in blade load,reduced external head and efficiency,and a series of effects on noise and vibration during impeller operation.Taking effective measures to control the generation of cavitation is of great significance for the stable operation of fluid machinery.In this paper,NACA 0015 hydrofoil and low specific speed centrifugal pump are taken as the research objects.A method for actively cavitation control of bionic structures on the surface of the blade is proposed through theoretical analysis,experimental research and numerical simulation.The cavitation flow and hydrodynamic characteristics of NACA 0015 airfoil,the cavitation characteristics of low specific speed centrifugal pump,the change law of cavitation flow,and the variation law of blade load are systematically studied.The main research contents and conclusions are as follows:（1）The numerical simulation of cloud cavitation of three-dimensional NACA0015 hydrofoil under typical working conditionsσ=0.8 was studied,and on this basis,the influence of bionic structure of hydrofoil surface arrangement on cavitation performance was studied,and the cavitation flow field and hydrodynamic characteristics of hydrofoils with different parameters were numerically simulated and studied.The results show that when the chordwise position of the bionic structure is L=0.3c,the width is b=0.15δ_max,and the angle isθ=14°,the suppression effect is the most obvious,compared with the prototype hydrofoil,the number of cavitations is reduced by 24%,the vibration frequency of hydrofoils is reduced by 23%,the lift-drag ratio is increased by 4.73%,and the thickness and strength of the retrojet are significantly weakened.（2）Combine experimental and numerical simulation methods to explore the instability of cavitation flow of centrifugal pump.The numerical simulation of the unsteady cavitation flow inside the centrifugal pump is analyzed,and the results show that when the cavitation allowance of the device is reduced to a certain extent,the head has a cliff-like drop.This is due to when the cavitation develops to a certain extent,the cavitation occupies most of the flow channel,and the blade load pressure will suddenly decrease,resulting in the loss of functional ability of the blade.The extra-experimental characteristics and cavitation performance are compared with the numerical simulation values,and the experimental values are in good agreement with the simulated values,which proves that the numerical simulation and cavitation model are reliable.（3）Based on the effectiveness of bionic hydrofoils arranged in hydrofoils and the accuracy of numerical simulation of centrifugal pumps,the applicability of bionic structures in low-specific speed centrifugal pumps was studied by numerical simulation method,and the cavitation flow mechanism and the mechanism of action of bionic structures inside the impeller were studied.It was found that the bionic structure arranged on the back side could effectively inhibit the initial generation of cavitation,while the bionic structure arranged on the working face greatly delayed the occurrence of cavitation in critical cavitation and fracture cavitation,and increased the operating range of the pump.（4）The bionic structure on the back reduces the volume of the primary cavitation by 44%,which significantly reduces the low pressure area generated in the leading edge of the blade,reduces the energy dissipation at the back position,increases the low vortex viscosity area at the inlet area,and reduces the vortex intensity.Compared with the prototype centrifugal pump model,the head at critical cavitation point increased by 3%,the cavitation volume decreased by 20%,the head at the cavitation fracture point increased by 10%,and the cavitation volume decreased by 18%.Moreover,the bionic structure arranged on the working surface effectively reduces the distribution of low pressure area,optimize the internal flow field structure of the centrifugal pump,weaken the pressure pulsation at the impeller inlet of the centrifugal pump and near the volute,so as to delay the development of the internal cavitation of the centrifugal pump and improve its cavitation performance.