ADVERSE REYNOLDS NUMBER EFFECT ON MAXIMUM LIFT OF TWO DIMENSIONAL AIRFOILS

An adverse Reynolds number effect on C !max of NACA 8318 airfoil was experimentally investigated, using a rectangular wing model with an aspect ratio of 5.7. At a little lower Reynolds number than that of old test data by NACA, a slight decrease of the C !max , namely the adverse effect was confirmed. Furthermore, short bubble that did not play a major role in the old explanation given by Tani was also observed at the condition showing the adverse effect. The adverse effect is clearly based on the forward movement of turbulent separation point, and we assumed new mechanism that the forward movement was dominated by the initial state of turbulent boundary layer at reattachment point. At relatively higher Reynolds numbers, large adverse effect was also obtained and it strongly originated in three-dimensionality of separated flow. This means such threedimensionality is more important in the study on C!max of two-dimensional airfoils in addition to the new mechanism, because turbulent separation has almost three-dimensionality at high Reynolds numbers.