A STUDY ON MECHANISM OF ACOUSTIC CONTROL OVER AIRFOIL FLOW IN UNIFORM INCOMING FLOW

An experimental study on the acoustic control of separated flow on a 2-dimensional airfoil at low speed ( Re =3—6×10⁵) and high angle of attack was completed at the Turbine  Aero-Acoustics Laboratory,SJTU.Based on the comparison of test results with or without the acoustic control in uniform incoming flow,the benefits of the acoustic control (improvement of lift and drag coefficients),the effects of the parameters of exciting sound (sound pressure level SPL and frequency f_s ) and the variation of flow parameters in the boundary layer on the suction side of airfoil (mean flow velocity,turbulence and the spectrum of fluctuating velocity) have been investigated,and some valuable conclusions have been obtained for exploring the mechanism and exploiting the acoustic control.Two threshold values of SPL for the exciting sound have been defined.There is only one optimum frequency,corresponding to the fundamental frequency of acoustic cross-resonance of the testing tube,at which the SPL of exciting sound and the enhancement of lift coefficient will approach maximum value simultaneously.It is evident that the optimum frequency of exciting sound depends not only on the cross-resonance of the testing tube,but also on the dimension of Large Scale Orgnized Structure Vorticity (LSOSV) induced by the exciting sound.Finally,a tentative idea on the non-linear analysis of sound-turbulence interaction in the separated boundary layer has been proposed.