双平板叶栅绕流的流动结构及其激励特性研究

绕流叶片的非稳态流动及其尾迹涡结构是诱发水力机械振动的主导因素。以横向布置的一对平板叶栅为研究对象,基于LES计算雷诺数在4.8×104下的三维绕流流场,分析绕流流场涡演化结构、升阻力及压力脉动等特性,以揭示尾迹干涉下平板绕流的流场结构及其激励机制。结果表明:该雷诺数下,单平板绕流平板表面存在错列布置的发卡涡结构,绕流尾迹呈现出高度的三维特性;双平板叶栅绕流状态下,上、下游平板间的间隙流动结构有明显抑制上游平板表面涡结构演化的作用;平板受力在模式H和模式L之间不断切换,且升力波动的幅值随阻力的增大而增大,尾迹干涉下下游平板受力的模式切换频率升高,升力波动幅值也增大;平板表面压力脉动的主要激励源为平板尾涡脱落。尾迹干涉下平板绕流及受力分析,可为水力机械叶片尾迹干涉下的流动主动控制提供参考。

Flow Structure and Excitation Characteristics of Flow around Double Plate Cascades

Unsteady flow and vortex-wake structure of flow around a blade are the main factors inducing hydro-mechanical vibration. A pair of plate cascades arranged transversely was taken as the research object. The three-dimensional flow field was calculated based on the large-eddy simulations (LES) when the Reynolds number was 4.8×104, and the characteristics of vortex evolution structure, lift and drag coefficients and pressure pulsation were analyzed. The flow field structure and excitation mechanism of the flow around the plate under wake interference were discussed. Results showed that the hairpin vortex structure on the surface of the single plate is staggered and the wake shows a high degree of three-dimensional characteristics under this Reynolds number. The flow structure between the upstream and downstream plates under the cascade flow regime significantly restrained the evolution of vortex structure on upstream plate surface. The force of plate was continuously switched between the regime H and regime L, and the magnitude of lift fluctuation was increased with the increase of drag. The regime switching frequency of downstream plate force under the wake interference and the amplitude of the lift fluctuation were both increased. Analysis on the results of flow and force around plate under wake interference can provide reference for active control of hydro-mechanical blades wake interaction, which would facilitate the development of the design to control vibrations and noise.