The physics of control by pulsed blowing on a NACA 64 3 - 618 natural laminar flow airfoil is studied using hot-film anemometry. Measurements in the uncontrolled separated shear layer indicate that vortex shedding is taking place due to the Kelvin–Helmholtz-type inviscid instability. Steady and pulsed external acoustic excitation is used as well to decouple the frequency content of the perturbation from the vorticity introduced by the jet. Acoustic control introduces either the most unstable frequency or harmonics of carrier frequency in the most unstable range, which amplify exponentially in the separation region yielding a significant delay of the separation location to approximately 55% chord. Experimental data suggest that pulsed jets introduce higher-order harmonics of the low-frequency pulsing as well, amplifying the natural disturbances in the laminar separation. Phase-averaged wavelet analysis is used to study the control physics within a single pulsing period. It is shown that a jet-induced high-frequency content convects downstream of the jets at approximately the freestream velocity. A second packet of jet-induced frequency content is convected inside the boundary layer at a slower speed. As the second packet interacts with the laminar separation, natural vortex shedding is enhanced. The vortex shedding induces momentum near the wall and temporarily calms the separation. After the convected turbulent structures have passed, vortex shedding subsides, and the boundary layer briefly loses momentum near the wall until the next set of structures return.


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    Title :

    Pulsed Jets Laminar Separation Control Using Instability Exploitation


    Contributors:

    Published in:

    AIAA Journal ; 52 , 1 ; 104-115


    Publication date :

    2014-01-01




    Type of media :

    Conference paper , Article (Journal)


    Type of material :

    Electronic Resource


    Language :

    English