Aerodynamic and acoustic performance of an airfoil with leading edge serrations

Abstract

This thesis describes an experimental investigation into the aerodynamic and acoustic effects of leading edge (LE) serrations on a NACA0012 airfoil, and the specific geometrical parameters of the serrations that influence the airfoil’s performance. It is found that the presence of LE serrations degrades the lift to drag ratio (L/D) of the airfoil in the pre-stall region, owing to a decrease in maximum lift and an early increase in drag. However, the ability to retain lift and reduce drag in the post-stall region enables the airfoil with LE serrations to maintain a slower pace for the decreasing L/D. Serrations with a smaller height and larger wavelength tend to produce higher lift and lower drag. The presence of LE serrations is beneficial for reducing/eliminating an airfoil’s tonal noise, but in the case of broadband noise at higher angles of attack (above 6°), LE serrations are usually detrimental as they increase the sound pressure level (SPL) at medium to high frequencies. Height is found to be essential to the LE serrations’ influences on both tonal noise and broadband noise: larger height is beneficial to tone reduction/elimination, but it causes a higher broadband SPL at frequencies above 1.5kHz. Observations made from the current study generally agree well with the assumption that LE serrations play a similar role as vortex generators. The benefits of maintaining lift after stall and tone reduction/elimination can both be attributed to the turbulent boundary layer caused by the generated vortices. The significant increase of broadband noise could be caused by the overly large sizes of the serrations in the current study, thus explorations of the effects of serrations with smaller sizes (as well as many other parameters) should be made in the future study.

Date of Award	2017
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology