Study On The Control Mechanism Of Cavitation Flow In The Pectoral Fin Segment Of Humpback Whale

In recent years,with the development of ultra-high speed and large displacement turbomachinery,the demand for anti-cavitation performance of turbomachinery is increasing gradually.In order to reduce the cavitation volume of the blade,suppress the development of cavitation,and improve the lift and drag performance of the blade,it was found that the pectoral fin nodal of Marine life humpback whale has good hydrodynamic characteristics and anti-cavitation characteristics through research.Therefore,NACA 63₄-021 airfoil,which is geometrically similar to the pectoral fin section of humpback whale,was selected for numerical simulation.The control mechanism of bionic airfoil on cavitation flow is expounded.The specific research ideas and conclusions of this paper are as follows:（1）Firstly,the lift and drag characteristics and flow field characteristics of basic and bionic airfoils under different flow parameters are numerically simulated by means of large eddy simulation method.The large eddy simulation method can clearly describe the flow field in the large scale vortex and broken small vortex structure,so as to interpret based airfoil and flow angle of attack to bionic mechanism of the influence of the airfoil cavitation morphology,reveals the front bump airfoil space-time evolution of three-dimensional vortex structure.It is founded that the front bump has good inhibition to the cavitation.（2）The pressure pulsation on the suction surface and flow field of the basic airfoil and the bionic airfoil at different attack angles was compared in detail.The amplitude and frequency characteristics of pressure pulsation in different cavitation forms were explored,and the relationship between pressure pulsation and the frequency of cavitation shedding was analyzed.By using the method of fast Fourier transform,the amplitude change of pressure coefficient of bionic airfoil relative to the basic airfoil was quantitativelystudied.（3）By changing the amplitude and wavelength of the bionic airfoil,the control mechanism of structural parameters on the cavitation flow of the airfoil was explored.By analyzing the position of the separate vortexes in the flow field,the influence mechanism of the lift and drag characteristics of the airfoil is clarified,and it is found that the streamwise vortexes have a certain influence on the transition of cavitation morphology.The results show that the large-amplitude bionic airfoil has better anti-cavitation performance,which can inhibit the occurrence of cloud cavitation and reduce the instability of hydrodynamic performance.Small wavelength bionic airfoil can relieve the unstable shedding of cloud cavitation and reduce the pressure pulsation of the flow field.In this paper,the mechanism of cavitation suppression is studied in detail,with emphasis on the interaction mechanism between cavitation morphology and vortex structure and the relationship between pressure pulsation and cavitation abscission dynamics.The inhibiting effect of the bionic airfoil on the cavitation volume is proved,and the quasi-periodic law of pressure pulsation and cavitation shedding is clarified.It is concluded that the velocity variation of cavitation region is the main cause of pressure pulsation.This study will promote the development of anti-cavitation bionic airfoil design to a certain extent,and has reference significance for the research of bionic airfoil in the field of cavitation control.