Title:	Low-noise solutions for realistic landing gears
DNr:	SNIC 2014/1-73
Project Type:	SNIC Medium Compute
Principal Investigator:	Ciarán O'Reilly <ciaran@kth.se>
Affiliation:	Kungliga Tekniska högskolan
Duration:	2014-03-03 – 2015-04-01
Classification:	20301 20306 20303
Keywords:

Abstract

Aircraft noise in the approach phase represents a significant health hazard for local communities and imposes costly constraints on flight schedules. Deployed landing gears are the main source of airframe noise, which contributes roughly half of the total noise emission for typical commercial aircrafts in the approach phase. The proposed work considers the aerodynamic noise generated by the main and nose landing gears of a 100-seat regional aircraft. For this purpose, a so-called hybrid approach is used. This consists of separating the sound generation by the flow dynamics and the sound propagation. Thus, there are two main areas of investigation: the flow computations and the acoustic propagation. In addition, we introduce and investigate a novel approach to reduce the computational cost of sound propagation, via a modal reduction technique. Time-dependent flow computations are needed to account for the unsteady phenomena associated with sound. A high mesh resolution is required to resolve small-scale turbulent features contributing to high frequencies. Similarly, the sound propagation requires an appropriate temporal and spatial discretization, with a high number of points per wavelength. The objectives of the proposed work are as follows: 1) To investigate the flow dynamics and acoustics of highly detailed main (half-scale) and nose (full-scale) landing gear geometries. The contribution of individual components is to be examined. 2) To examine two realistic low-noise configurations (called LN1 and LN2) based on noise-reduction devices with high Technology Readiness Level (TRL). LN1 and LN2 are designed based on a combination of fairings, hole caps and air deflectors. The flow and acoustic fields of LN1 and LN2 will be compared with that of the baseline design. 3) To compare three different methods for computing the noise propagation, with a view to understanding the impact of simplifying assumptions on the computed acoustics and to informing future aero-acoustics investigations. 4) To perform a modal reduction of the near-field surface pressure fluctuations, via Dynamic Mode Decomposition (DMD), and examine the feasibility of reconstructing the far-field noise with only a few of the most energetic modes. A hybrid approach is used to compute the far-field noise generated by the landing gears. The first step is to compute the flow field for the baseline and low-noise configurations LN1 and LN2. We use a commercial Navier-Stokes solver, STAR-CCM+, to perform a Detached-Eddy Simulation (DES) with high resolution in the near-wall regions. The Reynolds number is 10⁶. Two angles of incidence and two yawing angles are considered, to span a range of different possible approach states. The effect of the turbulence model used is studied. A partner research group at TCD will be responsible for an experimental investigation on the same geometries, which will allow a valuable comparison of the numerical and experimental data. Sound sources are characterized and sound propagation methods are used to investigate the far-field acoustics. Three techniques are considered: the Curle, Ffowcs Williams-Hawkings and a combination of FWH with DMD.