Study on Separation Bubble on the Constant Thickness Airfoil with Circular Leading Edge

对半径为10 mm的圆形前缘等厚翼型的均匀流动和加速流动进行了实验研究，研究了分离特性、分离气泡的结构、分离气泡内的流动特性以及表面压力与表面速度的关系。基于翼型厚度的雷诺数为2.65x10^4，迎角改变为0ﾟ-5ﾟ。结果表明：(1)在边界层过渡区发生分离时，分离气泡中的大尺度涡中心位于分离气泡的后半部分附近。分离气泡后半部分的分离流线弦向梯度大于前半部分。在湍流边界层分离的情况下，这一现象是相反的。(2)关于再附着，能量通过剪切涡从主流提供给分离的剪切层，从再附着点提供相当于从分离气泡到主流的卷吸体积的反向流量。(3)在边界层过渡区分离的情况下，雷诺切应力在大尺度涡中心下游变得最大，而在湍流边界层分离的情况下在大尺度涡中心的上游。(4)在过渡区分离时，再附着点位于分离气泡内恒压区后面的压力恢复区内。在湍流边界层分离的情况下，再附着点出现在压力恢复完成后。(5)在过渡区分离时，最大压力波动出现在再附着点附近，而在湍流边界层分离的情况下，最大压力波动发生在再附着点的上游。

Uniform flow and accelerated flow around the constant thickness airfoil with circular leading edge of 10mm radius has been studied experimentally on the characteristics of separation, the structure of separation bubble, the characteristics of flow in the separation bubble and the relation between surface pressure and surface velocity. Reynolds number based on airfoil thickness is 2.65x10^4 and angles of attack are changed 0ﾟ - 5ﾟ. The results are as follws.(1) In case of separation in transition region of boundary layr, the center of large-scale vortex in the separation bubble is found around the latter half of separation bubble. The chordwise gradient of separation-streamline at the latter half of separation bubble is larger than that at the front half of it. In case of separation in turbulent boundary layr, the phenomena are reversed.(2) Relating to the reattachment, the energy is supplied from main flow to separated shear layr by means of shear vortex, and the reversed flow volume equal to the entraining volume from separation bubble to main flow is supplied from reattachment point.(3) Reynolds shear stress become maximum downstream the center of large-scale vortex in case of separation in transition region of boundary layr, but upstream the center of large-scale vortex in case of separation in turbulent boundary layr.(4) In case of separation in transition region, the reattachment point is located in the pressure recovery region just behind constant pressure region in the separation bubble. In case of separation in turbulent boundary layr, the reattachment point appears after the completion of the pressure recovery.(5) Maximum pressure fluctuation occurs around the reattachment point in case of separation in transition region, but upstream the reattachment point in case of separation in turbulent boundary layr.