Trailing-edge noise generation from a flat-plate aerofoil interacting with a prescribed vortex

Abstract

Aerodynamic noise generated by aerofoil-vortex interaction has widely been studied in the past where the primary noise source mechanism is the scattering of the vortex at the leading edge (LE) of the aerofoil. In this paper the secondary source mechanism-the subsequent vortical scattering at the trailing edge (TE)-is investigated in detail, which shows that the secondary source mechanism is mainly contributed by nonlinear effects as predicted by some analytical studies in the past. The present study is performed by employing high-resolution numerical simulations based on a prescribed non-singular vortex impinging on a flat-plate aerofoil with zero mean loading. The present work investigates both inviscid and viscous flow conditions. The inviscid flow condition is intended to support and extend from the existing theoretical works, whereas the viscous one leads to more realistic findings. The current viscous study involves laminar boundary layers and their convective instability travelling with the impinged vortex. One of the most notable observations made in this work is that the vortical scattering at the TE (in the absence of turbulent boundary layers) may become a dictating source of noise at high frequencies (surpassing the primary source at the LE) across a wide range of observer angles for both inviscid and viscous flow conditions. It is found that the high-frequency dominant source is produced by secondary near-wall vortices that are induced as a result of nonlinear interactions between the aerofoil and the impinging vortex. This new discovery makes a contrast to the existing knowledge on aerofoil-vortex interaction noise in which the secondary source is normally assumed inferior to the primary at all frequencies.

Challenges and opportunities for low noise electric aircraft

“…However, recent evidence may suggest that the trailing edge may contribute appreciably to turbulence-airfoil interaction noise. 108,109…”

“…However, recent evidence may suggest that the trailing edge may contribute appreciably to turbulence-airfoil interaction noise. 108,109 In 1975, Amiet published a landmark paper 110 that forms the foundation of leading edge noise prediction to this day. Amiet's approach and its extensions were reviewed by Roger and Moreau, 111 and related to trailing edge noise prediction models.…”

Mitigation of transonic shock buffet on a supercritical airfoil through wavy leading edges

“…In this study, a different approach is used based on a frequency filtering of the flow 41 . The advantage is that once the flow field is filtered, it is still possible to analyse its evolution over time and results are not limited to a contour of the modes.…”

Downstream porosity for the reduction of turbulence–aerofoil interaction noise

“…The phase inversion arises because its sense of rotation is opposite to that of the initial vortex. The existence and significance of secondary vorticity in aerofoil noise 415 generation were first recognised by [32] in a fundamental numerical study of leading edge noise due to flat plates. In [32] it was shown that secondary vorticity is induced as a result of nonlinear interactions between the aerofoil and the impinging vortex.…”

“…The existence and significance of secondary vorticity in aerofoil noise 415 generation were first recognised by [32] in a fundamental numerical study of leading edge noise due to flat plates. In [32] it was shown that secondary vorticity is induced as a result of nonlinear interactions between the aerofoil and the impinging vortex. This secondary vortex then convects towards the trailing edge and was a significant source of trailing edge noise.…”