Appropriate Timing to Start Suppressing a Dynamic Stall

The appropriate timing to start controlling a dynamic stall was studied to find an optimum timing to start control just before separation and a way to reduce the total amount of energy to suppress separation. The dynamic stall of an airfoil in pitching-up motion was adopted because the time when separation occurs can be determined beforehand. The timing of control was defined as the interval from the start of control to the onset of separation without control. A wall-jet ejected from a thin slit near the leading edge of the airfoil at a constant velocity was used to suppress the separation. Many combinations of the timing of ejection and velocity of the jet were tested to determine the optimum amount of energy required to suppress the stall. It was found that, within the limits of our experimental conditions, there exists an optimum combination.