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

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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.