| Popis: |
This paper introduces the effects of disturbed incoming flow on the acoustic control of separated flow over a low-speed 2D airfoil at large angles of attack, including the benefits of acoustic excitation, the influence of sound excitation parameters, and the flow parameter variation in the boundary layer. Based on the testing results, the first (minimum) and second (effective) threshold values of the sound pressure level of the exciting sound are defined. It is indicated that the benefit of the lift coefficient, reduced by the exciting sound, will rapidly decrease along with the increased turbulence of the incoming flow. The peak lift coefficient, as well as the effective threshold value of the sound pressure level, will still gradually increase in the same situation. The oscillating incoming flow does not influence the acoustic excitation for the low-speed 2D airfoil at large angles of attack in either uniform or disturbed incoming flow. Finally, for the evaluation of the threshold value of the sound pressure level and optimum frequency of the exciting sound, an idea is proposed for the nonlinear analysis of the sound-turbulence interaction in the separated boundary layer. (Author) |
