激振控制分离流动的初步研究

A PRELIMINARY INVESTIGATION OF THE CONTROL OF SEPARATED FLOW BY MEANS OF EXCITATION

采用流场显示与测力相结合的方法研究平片激振控制二维锐缘分离流动问题。结果表明:若模型原始流态是闭式分离泡状态,适当频率的激振可使分离泡减小,升力和阻力也相应地减小。达时激振减阻的最佳Strouhal数(St_(x_(ro))=(fx_(ro)/U_∞)范围为3～5。若模型原始流态是完全分离流动,适当频率的激振状态与未激振状态相比,模型升力明显增加;相应地,流态从完全分离流动转变成闭式分离泡。激振增升的最佳Strouhal数(St_c=fc/U_∞)范围为0.7～2.5。

Force measurements combined with flow visualization are used to investigate the control of two dimensional leading-edge separation by means of flap oscillation. It is found that the results of control are related to the model natural flow patterns. When the natural flow pattern is a closed separation bubble, the excitation causes a lift loss. A reduction of reattachment length and a reduction of the drag of the model can be achieved by proper frequency excitation.The most effective Strouhal number range based on the reattachment length and the main stream velocity for drag reduction is 3- 5. When the natural flow pattern is full separation, proper frequency excitation changes the flow field into a closed separation bubble and a lift increment is achieved. The most effective Strouhal number range based on the chord of the model and main stream velocity for lift increment is 0.70-2.5.