An Aerodynamic Noise Reduction Study for Airframe Noise from Flap Tips

Abstract

In order to reduce aerodynamic noise from aircraft flap tip, we design two types of low noise flap tips named “Small Barrier” and “Leading Edge Cut”. The former has small cubes on the upper surface near the leading edge at flap tip. The latter has cut leading edge which location is moved backward. Both low noise flap tips are designed to induce flow separation on the flap upper surface. It takes a reduction of aerodynamic lift around the flap tip. Then, it makes flap tip vortexes weaker which causes aerodynamic noise. Other aspect of the flap tip design, we focused on usefulness to apply them to actual aircrafts. The shape is so simple that weight penalty is negligible. And there is not any influence of aerodynamics on cruise condition. In order to evaluate the characteristics of noise and aerodynamic force of these low noise flap tips, wind tunnel testing was conducted using on a simplified high-lift configuration model with sweptback wing (OTOMO2). The result shows that the low noise flap tips have about 1 to 2dBA(SPL overall) noise reduction in wide emission angles at approach angle of attack. The wing lift and drag reduces slightly, but lift per drag difference from original model is almost nothing.