Spoiler aerodynamics and aeroacoustics

Abstract

This research investigates the aerodynamic and aeroacoustic characteristics of a deployed spoiler used for noise abatement during steep aircraft approaches. When deployed on a multi-element wing, the spoiler's flow field is influenced by the lifting bodies' aerodynamic characteristics and associated circulation changes. Consequently, it is difficult to separate the fundamental flow field characteristics generated by the spoiler from the influence of the other external aerodynamic bodies. To isolate the flow topology and noise sources generated by the spoiler, this study adopts a systematic methodology starting from simplified non-lifting geometries and progressing towards more realistic aircraft wing configurations. This approach not only allows for the characterisation of the flow field and the flow-induced noise sources generated by the spoiler but also assesses the influence of each contributing aerodynamic device on the spoiler's performance.

Initially, a spoiler mounted on a flat, non-lifting surface is examined to establish a fundamental understanding of the flow topology and associated noise sources. Both experimental and numerical methods are employed. Simulations are performed using a Lattice Boltzmann solver, ProLB. These numerical simulations are validated against an experimental dataset. Three dominant flow structures are identified; an upstream separation bubble forming a horseshoe vortex, ground edge vortices attached to the base mounting plate, and an arch-type broadband wake. The unsteady pressure fluctuations generated by these flow features on the spoiler and mounting surface lead to acoustic noise radiation, with the scattering of the ground edge vortices along the spoiler's side-edges identified as primary noise sources. These topological features further influence the acoustic scaling behaviour of a wall-mounted spoiler plate at different deflection angles and frequencies.

The study further addresses spoilers integrated with lifting surfaces by investigating the aerodynamic and acoustic effects of mounting a spoiler on a lifting airfoil and, subsequently, a multi-element wing. In order to achieve this aim, a Kevlar-walled hybrid test section extension was designed to measure the far-field acoustics response of a spoiler deployed on a NACA 0012 airfoil. Numerical simulations reveal that when mounted on a lifting airfoil, the circulation significantly alters the spoiler's flow topology, resulting in a larger adverse pressure gradient upstream of the spoiler, leading to earlier boundary layer separation and shear layer breakdown, larger horseshoe vortices, and the generation of vortex shedding due to the shear layer roll-up along the spoiler's and the airfoil's trailing edge.

In the multi-element wing configuration, the incoming confluence between the boundary layer of the main element and the shed wake from the trailing edge of the slat suppresses upstream separation. Consequently, it changes the effective angle of the incoming flow velocity vector. This induces a shift in the primary noise sources towards the spoiler's trailing edge. A distinctive tone is generated due to cavity resonance between the spoiler and the downstream surface of the main element.

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Identifiers

ORCID for Owen Parnis: orcid.org/0009-0009-6347-8873

ORCID for David Angland: orcid.org/0000-0001-5451-2763

ORCID for Zhiwei Hu: orcid.org/0000-0001-6737-4363

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