Numerical Simulation of Landing Gear Noise via Weakly Coupled CFD-CAA Calculations

Abstract

The present work is relevant from the numerical prediction of aircraft noise via aeroacoustics hybrid methods. It is part of a more extensive effort, which final objective is the development of a robust and accurate CFD-CAA weak coupling methodology. Within this framework, we focus here on the so-called surface coupling approach, a technique that allows conducting weakly coupled CFD-CAA calculations. Such approach (which had been previously developed and validated on simpler cases) is here applied to a ralistic problem of aircraft noise, given by the acoustic emission of a nose landing gear in approach flight (a configuration that was addressed in the Airbus LAGooN program). For doing so, several preliminary tasks are first addressed, which are carefully handled and thoroughly detailed. Two CFD-CAA coupled calculations are then conducted, both being based on i) a same CFD dataset coming from an unsteady aerodynamic calculation (zonal DES), and ii) two distinct CAA calculations of different characteristics ; first, a CFD-CAA calculation is conducted for the so-called 'baseline' configuration (i.e. isolated gear within a free-field flow), so as to validate the coupling procedure, as well as to generate a reference solution for subsequent assessment of the mean flow effects induced by the experimental set-up. The validation of the coupling procedure is conducted via a direct comparison of the CFD-CAA results with either experimental or numerical (CFD, CFD-FWH) outputs obtained in the near-, mid, and/or far-field. With the view of assessing the mean flow effects, an alternative CFD-CAA calculation is then performed, which incorporates the realistic sheared jet flow characterizing the anechoic facility. This allows assessing the (partial) convection and refraction effects induced by such jet mean flow, which helps underscoring better the relevance of the present CFD-CAA hybrid approach when it comes to handle real-life noise problems.

An advanced hybrid method for the acoustic prediction

“…Thanks to the various methodological outcomes they led to, these studies made it possible to develop an advanced CAA-based hybrid approach, which integrates and connects altogether the diverse aspects of the problem, whilst accounting for their interactions. Such approach was validated through an application to various acoustic problems of increasing complexity [23,24,31] (some of which are presented hereafter).…”

Landing Gear Noise Identification Using Phased Array with Experimental and Computational Data

“…Regarding these spurious artifacts observed at higher frequencies for the cross-shaped array results derived from the second Article in Advance / BULTÉ AND REDONNET CFD-CAA computation, a plausible explanation for this could come from the fact that, as was extensively documented in [37], the CFD unsteady dataset that was stored to be acoustically exploited through CAA [37] (or IM [33]) exhibited sporadic but rather intense bursts. The latter originated from all the hydrodynamic occurrences (vortices, etc.)…”

“…IM) stage to resolve accurately enough all of the unsteady aerodynamic occurrences, especially over the higher part of the frequency spectrum [34]. It is likely that, in the present case, these spurious noise waves inherited from the CAA conversion of CFD-originated hydrodynamic occurrences [33,37] were interpreted by the sensor array algorithm as additional sources, which were then logically-although abusively-located in the NLG wake region. The observation that only the C19-based numerical outputs were contaminated could be logically explained by the fact that, compared with its F2 starshaped counterpart, the C19 cross-shaped array was larger, as well as centered slightly downstream of the gear axle (see Fig.…”

“…For more details about these CFD-CAA weakly coupled calculations and their underlying hybrid methodology, the reader is referred to [32,37].…”

“…After that, the CFDbased noise generation stage previously simulated was weakly coupled with a CAA-based noise propagation one, the latter conducted using ONERA's sAbrinA solver [34][35][36], which is a timedomain CAA code that solves the perturbed nonlinear Euler equations using high-order finite-differences schemes. The 19th and 21st AIAA Aeroacoustic Conference provided an opportunity to present these CFD-CAA hybrid calculations and outcomes [33,37], which were then thoroughly documented in a dedicated journal paper [32] and are briefly summarized hereafter.…”