基于弱可压的混流式水轮机流动特性数值研究OA

Due to the high pressure difference between the upstream and downstream of high-head Francis turbines,the water flow exhibits weak compressibility under high pressure,which affects the distribution pattern of the internal flow characteristics of the units.To further investigate the influence of weak compressibility on pressure pulsation and vortex characteristics of turbines,this paper considers the weak compressibility of water flow and conducts an unsteady numerical study on part-load flow characteristics of the Francis99 high-head model turbine.The results indicate that the patterns of pressure pulsation signals in the bladeless area and the runner are quite consistent,whether compressibility is neglected or considered.When compressibility is considered,both low-frequency high-amplitude pressure pulsations and high-frequency low-amplitude pressure pulsations in the draft tube are predicted,closely aligning with the test results.This finding indicates that weak compressibility significantly influences the accurate capture of flow information in the draft tube.After the synchronous and asynchronous decomposition of pressure signals,it is found that the asynchronous component,which characterizes the rotation of the vortex rope,dominates the motion of the draft tube vortex rope.Furthermore,when water flow compressibility is considered,the captured helical vortex rope in the draft tube exhibits a continuous structure throughout the entire evolution cycle.The backflow zone corresponds to the vortex rope location,indicating that the area occupied by the vortex rope is primarily dominated by backflow motion.