Abstract
Theme IRFRAME noise from aerodynamically clean airframes A is assumed to be trailing-edge noise caused by convection of the wing turbulent boundary layer past the wing trailing edge. Resulting maximum flyover noise is predicted from an existing solution for trailing-edge noise plus estimates of turbulent boundary-layer integral scale length and turbulence intensity. Typical airplanes with retracted or well-faired landing gear but with wing-mounted engine nacelles and extensive trailing-edge flap-track shields generate about 8 dB more than this minimum trailing-edge noise. Resulting predicted acoustic intensity varies with airspeed t o the fifth power, in agreement with a linear regression analysis of flight data. ' Trailing-edge noise has been previously inferred' to be the mechanism for airframe noise because of the observed fifthpower velocity dependence. In contrast, other analyses 3.4 have assumed a lift dipole directivity associated with fluctuating-drag noise mechanisms and have predicted a sixthpower velocity dependence.
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