| Cavitation flow is a kind of multi-scale cavitation flow with phase change,turbulence and other non-constant characteristics,accompanied by complex hydrodynamic load changes,resulting in cavitation erosion,noise and vibration and other hazards,is the difficult problem faced by hydraulic machinery,underwater high-speed navigation body.In order to improve the working performance of equipment,currently in engineering composite materials and other light elastic materials are widely used,the structure will be under fluid load vibration deformation,in cavitation flow in the fluid-solid coupling phenomenon is more prominent,the flow field and structural safety can cause serious impact.Therefore,it is of great theoretical significance and practical application to master the fluid-structure coupling characteristics and influence rule of non-constant cavitation flow to solve the negative effects of cavitation and improve the working performance of equipment.The main work and results carried out in this paper are:Firstly,this paper establishes a numerical computational model of fluid-solid coupling for the cavitation flow field with the hydrofoil as the base model.The computational model adopts the large eddy simulation(LES)method to solve the turbulent flow,the volume of fluid(VOF)domain method to simulate the gas-liquid interface,the Schnerr-Sauer cavitation model to simulate the cavitation phase change process,the finite element method(FEM)to solve the structural deformation and displacement,and the data interaction at the solid-liquid interface under the tight coupling strategy to complete the fluid-solid coupling calculation.The validity of the computational model is verified by comparing and analyzing the numerical simulation results with the existing experimental results.Secondly,in order to study the effect of hydroelasticity on the cavitation flow field,the cavitation flow of NACA66 rigid and elastic hydrofoils is simulated based on the established numerical calculation model of fluid-solid coupling.By comparing the cavitation patterns of rigid and elastic hydrofoils,it is found that although hydroelasticity inhibits the development of cavitation and the cavitation evolution period is reduced,the cavitation presents a broken state,the pressure pulsation peak is larger and the fluctuations are more intense.In addition,the analysis of the turbulence characteristics of the wake field shows that the elastic hydrofoil produces greater turbulence intensity and integration scale in the incoming flow direction,the velocity pulsation is more intense,and the large scale vortices occupy more areas.Finally,the dynamic mode decomposition velocity field is used to capture the flow field modal characteristics,and it is found that the energy of the elastic hydrofoil is mainly concentrated in the first two orders of modes with larger coherent structure scales,while the high-frequency modes contain less energy with smaller coherent structure scales.Finally,based on the elastic hydrofoil cavitation fluid-solid coupling research basis,the evaluation study of composite materials to improve the hydrofoil cavitation phenomenon and hydrodynamic performance was carried out.By comparing the numerical calculation results of fluid-structure-acoustic coupling between bronze alloy and composite hydrofoil under two working conditions,it is found that the composite material can suppress the sheet cavitation attached to the suction surface of the hydrofoil and the top gap leakage vortex(TLV)cavitation,and lead to the decrease of hydrofoil lift and drag coefficient,but the pressure pulsation in the flow field becomes weaker and the lift-to-drag ratio of the hydrofoil increases.In addition,the composite material has a significant improvement effect on the wake field turbulence,reducing the turbulence intensity and integration scale,and the large scale vortices nearly disappear,effectively reducing the sound pressure level of the self noise and far-field radiation noise caused by cavitation. |
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