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

本文对均匀流和加速流绕半径为10 mm的等厚度圆弧前缘翼型的分离特性、分离泡的结构、分离泡内的流动特性以及表面压力与表面速度的关系进行了实验研究。基于翼型厚度的雷诺数为2.65x10^4，攻角变化范围为0 ° ~ 5 °。结果如下。(1)在边界层转捩区分离时，分离泡内大尺度涡的中心位于分离泡的后半部附近。分离泡后半部分的分离流线弦向梯度大于前半部分，在湍流边界层中分离时，情况正好相反。(2)与再附着有关的是，主流通过剪切涡向分离剪切层提供能量，再附着点提供相当于分离泡向主流卷吸量的反向流量。(3)在边界层过渡区分离时，雷诺切应力在大尺度涡中心下游最大，而在湍流边界层分离时，雷诺切应力在大尺度涡中心上游最大。(4)在过渡区分离的情况下，再附着点位于分离泡内恒压区后面的压力恢复区。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之后。(5)在过渡区分离时，最大压力脉动出现在再附着点附近，而在湍流边界层分离时，最大压力脉动出现在再附着点上游。

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.