Plato The Complete Works

Abstract

The high lift devices used on the wings of civil aircraft to increase lift at low flight speeds are contributors to the overall noise of aircraft at approach. Although there have been a number of recent steps forward in measurement and numerical modeling techniques for these sources there is still more work to be done in understanding the physical and acoustical reasons why they are so dominant. This paper outlines the analysis and interpretation of noise data from an aircraft in flight and the development of a semiempirical noise model for slats and flaps. Interference patterns observed in the data indicate that the sound radiation process involves multi-path sound propagation to the observer. A specific outcome of this observation was a notional source model which permitted the separation of noise radiation from the leading and trailing edges of acoustically non-compact flaps, and for slats a separation between two paths radiating from the slat trailing edge either above the slat or through the slat gap. Evidence for the fundamental source mechanisms is combined with standard theory of trailing edge and leading edge noise on isolated airfoils and acoustic image source techniques to explain why flap noise dominates the forward arc of the aircraft whereas slat noise dominates the rear-arc and hence why these sources are so significant for an observer on the ground.% (Author)