Unsteady Behavior of a Tip Vortex and Its Effect on the Unsteady Aerodynamic Force of a Downstream Blade

在低速风洞中，利用三传感器热线风速仪对周期性阵风作用下的叶尖泄漏涡和振荡叶片产生的叶尖泄漏涡的非定常特性进行了实验研究。实验中，叶片与风洞壁面之间留有间隙，在叶片中引入旋转圆柱的周期性阵风，在下游位置测量了三维流动速度，当尾流到达叶片前缘时，观察到叶尖涡减弱，涡心在叶片厚度方向上有较大幅度的振荡，从而阐明了涡心在叶片厚度方向上的振荡叶尖涡受到来流阵风的强烈影响。然后用热线风速仪检测了由振动叶片产生的叶尖涡。清楚地观察到叶尖涡与叶片振动的同相振荡。下游方向涡振荡相位的变化可以用平均流引起的涡对流来解释。在最后阶段，在振动叶片下游的平板上测量了非定常压力分布。由于振动叶片的叶尖涡的通过，表面压力显著降低，从而显著改变了平板上的非定常气动力。当叶尖涡穿过平板时，同时，本文还对非定常压力场进行了理论研究，其中发展了一种新的奇异性方法来估算具有任意涡量的非定常叶尖涡诱导的非定常气动力，位置

Unsteady behavior of a tip leakage vortex affected by periodic gust, and the one generated from an oscillating blade, were experimentally studied with a three-sensor hot-wire anemometer.The experiment was conducted in a low-speed wind tunnel in which a blade was set with a clearance between its tip and the tunnel wall.The periodic gust from rotating cylinders was introduced to the blade, and the three dimensional flow velocities were measured at downstream positions.When the wake reached the blade leading edge, the tip vortex was observed to diminish, and then it gradually regained the vorticity.The vortex center was found to oscillate with a large amplitude in the direction of blade thickness.It was thus clarified that the tip vortex was quite strongly affected by the incoming gust.The tip vortex generated from an oscillating blade was then detected by the hot-wire anemometry.The in-phase oscillation of the tip vortex with the blade oscillation was clearly observed.The change in the phase of the vortex oscillation in the downstream direction could be explained by the convection of the vortex due to mean flow.In the final stage, the unsteady pressure distributions were measured on a flat plate set at a downstream position of the oscillating blade, The surface pressure substantially decreased due to the passage of the oscillating tip vortex, and, thereby, the unsteady aerodynamic force on the flat plate was significantly changed.When the tip vortex moved across the flat plate, its position changed widely in the spanwise direction.The unsteady pressure field was accordingly changed in a wide area in the spanwise direction.A theoretical study was performed at the same time, in which a new singularity method was developed to estimate the induced unsteady aerodynamic force by the unsteady tip vortex with arbitrary vorticity and position.