Advanced computational modelling for aircraft landing gear unsteady aerodynamics

Abstract

High-fidelity turbulence modelling techniques have been applied to simulate the flow field around a simplified landing gear bay geometry. Three-dimensional Detached Eddy Simulation (DES) simulations have been performed for a cavity with the front 2/3 covered, as is representative of a nose landing gear bay. Resonant modes were observed in the shear layer, with frequencies in good agreement with the Rossiter cavity modes. The side-walls of the cavity, when compared to quasi-two-dimensional simulations with infinite span, were found to suppress the presence of acoustic modes inside the cavity, as well as causing a greater degree of breakdown in the shear layer, and changing the dominant resonant modes.

The geometry was varied to incorporate a single strut, and (separately) open rear doors, to test their separate contributions to the flow field in the landing gear bay. Both were found to produce small, high-frequency vortex structures, which interacted with the cavity shear layer and caused higher resonant modes to be present than with the clean cavity. A Large Eddy Simulation (LES) methodology has been developed and improved using the in-house solver software. An improved subgrid-scale model has been implemented, and the sensitivity of the solution to a variety of settings has been tested. Using a method for efficiently simulating flat-plate turbulence by tripping the flow using a small step, realistic wall-bounded turbulence has been modelled, with mean and turbulent quantities in good agreement with the literature for flat plate boundary layer flows.

The best-practice guidelines from this study were then applied to a turbulent flat plate upstream of the cavity with LES. The boundary layer turbulence structures were found to disrupt the coherence of the shear layer vortices, and lengthwise acoustic modes dominated inside the cavity in most cases. The sensitivity of this baseline simulation to several different parameters was investigated. These included the condition and thickness of the upstream boundary layer, the geometry around the lip of the cover, the turbulence modelling technique, and the spanwise length of the domain. The most significant difference was obtained by adding side walls, which was found to promote the development of shear layer resonance. Lower-mode tones were observed, with the associated pressure fluctuations being imposed and amplified inside the cavity.

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