NASA Langley Res. Ctr., MS 463, Hampton, VA 23681-0001
Response and acoustic radiation measurements from aircraft-type panels forced to vibrate by turbulent boundary layer flow are made in a quiet air duct facility and in a wind tunnel. Two types of aluminum structure are used: a newly developed panel with irregular, protruding, varying-thickness wedges at the upstream and downstream boundaries (fractal-type geometry) and a standard aircraft fuselage sidewall panel. Both panels have the same mass and exposed surface area to the flow. The new panel boundary has an extended perimeter with a gradual change in mass stiffness toward the center. The objective is to control the radiated acoustic pressure field. This is achieved by controlling the convective waves reflecting at the upstream and downstream boundaries of the panel. The geometry of the boundary is designed to induce a mismatch and randomness in wave motion along the direction of flow, resulting in significant attenuation of the amplitude of the incident and reflected waves.