Towards Understanding Aerofoils with Dual-Frequency Wavy Leading Edges Interacting with Vortical Disturbances

摘要

This paper presents numerical simulations of thin aerofoils with dual-frequency wavy leading edges (DWLE) interacting with an upstream vortical disturbance. The approach is based on the 3D compressible Euler equations and a single spanwise vortex which convects downstream with the mean flow inducing velocities at the aerofoil LE. The primary aim of this study is to demonstrate the noise reduction mechanisms of the DWLE by combining analysis of the LE source strengths with the corresponding far field acoustic properties. The motivation for introducing an additional LE frequency is to create an upstream root region with a similar source distribution as the (primary) downstream root, enticing destructive interference between the two. It is shown that the DWLE successfully achieves significant noise reductions in a small frequency band relative to single frequency WLEs of the same height. The suggested noise reduction mechanism is demonstrated by analysing the source strength distribution at the maximum noise reduction frequency, revealing points near the LE roots with equivalent source strengths which achieve phase shifts around π radians. As the LE height is increased the DWLE noise reduction peak shifts to a lower frequency. This is due to a greater streamwise distance between the two root regions, which increases the time lag between the upstream root and downstream root vortex-LE interactions, therefore reducing the out-of-phase frequency.