Research On Cavitating Flow And Turbulence Kinetic Energy Transport Around A Hydrofoil In OpenFOAM

Cavitation flow is the key problem in the stability of hydraulic machinery operation.It is urgent to investigate the effects of cavitation on the flow structure and energy evolution of hydraulic machinery or flow hydrofoil.In this paper,the open source software OpenFOAM was used to modify the turbulence model and numerical simulation is performed on the cavitation flow around the NACA66 hydrofoil.By comparing with the existing experimental results,the accuracy of the numerical calculation and the accuracy improvement effect of the modified model are verified.Based on the calculation results of the flow field,the flow state and dynamic characteristics of the unsteady cavitation flow around the two-dimensional hydrofoil are analyzed.By analyzing the relationship between turbulent kinetic energy distribution and cavity form,cavitation development stage and cavitation number,and based on turbulent kinetic energy transport equations,the interaction between turbulence and cavitation development is analyzed in depth.The cavitation internal flow mechanism is obtained on the level of turbulent energy transport.The main research content of this paper is as follows:(1)For the deficiency of the standard SST k-? turbulence model in the calculation of cavitation flow,the local compressibility correction and curvature correction were performed in OpenFOAM,and the modified model was used to simulate the unsteady cavitation flow around the hydrofoil.Compared with the experimental results and the original model calculation results,the accuracy of the numerical calculation and the accuracy of the modified model were verified.(2)Based on the calculation results of the modified model,we analyzed the cavitation volume distribution in the development cycle of cavitation,the distribution of cavitation and the distribution of flow lines in the shedding process,and the cavitation flow characteristics such as the pressure pulsation in the cavitation development cycle,and found that the modified SST k-? model has lower prediction of the frequency of cloud cavitation shedding but is closer to the experimental results,and more accurate unsteady cavitation flow state and dynamic characteristics are obtained.(3)By studying the distribution of turbulent kinetic energy in the cavitation development cycle under different cavitation numbers and along the streamlines,the relationship between the distribution of turbulent kinetic energy and the volume fraction of cavitation,the stage of cavitation development,and the cavitation number were analyzed.It was found that the distribution of turbulent kinetic energy was related to the degree of change in the volume fraction of cavitation.When the cavitation was in a stable state or non-cavitation occurred,the turbulent kinetic energy was close to zero.The more vigorous the volume fraction of vacuolar bubbles,the greater the turbulent kinetic energy.(4)An in-depth analysis of the relationship between turbulent energy transport and the development of cavitation reveals that the generation of cavitation,cavitation shedding movement and re-entrant jet will promote turbulence,and turbulence will in turn promote the production and collapse of cavitation.The movement of cavitation promotes the generation of turbulent kinetic energy and causes the turbulent kinetic energy to dissipate due to the viscosity of the fluid.At the vapor-liquid interface of the cavitation,the generation and collapse of cavitation will largely affect the transmission of turbulent kinetic energy.The operation is mainly reflected in the change of pressure action term and stress diffusion term;the viscous diffusion term only affects the transport of turbulent kinetic energy in the cavitation shedding stage of the hydrofoil wake region,and can be ignored in other stages.