Initial noise predictions for rudimentary landing gear

Abstract A four-wheel “rudimentary” landing gear (RLG) truck was designed for public-domain research, with a level of complexity which is manageable in current numerical simulations, and a weak Reynolds-number sensitivity. Experimental measurements of wall-pressure fluctuations are allowing a meaningful test of unsteady simulations with emphasis on noise generation. We present three Detached-Eddy Simulations (DES) using up to 18 million points in the high-order NTS code. The first is incompressible with the model placed in the wind tunnel, as requested for the 2010 workshop on Benchmark problems for Airframe Noise Computations (BANC-I), intended for force and surface-pressure studies. The second and third are at Mach 0.115 and Mach 0.23, with only one wall, a “ceiling” analogous to a wing (but infinite and inviscid), and are used to exercise far-field noise prediction by coupling the Detached-Eddy Simulations and a Ffowcs-Williams/Hawkings calculation. The results include wall-pressure, and far-field-noise intensities and spectra. The wall pressure signals in the three simulations are very similar and, in a comparison published separately, agree well with experiment and other simulations. In the absence of experimental noise data, the attention is focused on internal quality checks, by varying the permeable Ffowcs-Williams/Hawkings calculation surface and then by using only the solid surface. An unexpected finding at these Mach numbers is an apparent strong role for quadrupoles, revealed by a typical deficit of 3 dB in the solid-surface results, relative to the permeable-surface results. The solid-surface approach has variants, related to the presence of the ceiling (a plane of symmetry), which can increase this error further; there is little consensus on the exact configuration of the solid surfaces in the Ffowcs-Williams/Hawkings calculation procedure. Tentative theoretical arguments suggest that a balance somewhat in favor of quadrupoles over dipoles is plausible at Mach 0.115. However, the scaling of sound with Mach number does not follow the eighth power, as quadrupoles do in theory: it is closer to the sixth power. This trend gives a muddled theoretical picture, but agrees with the scaling observed in experiments. If it is confirmed, this finding will complicate airframe-noise calculations, and prevent the attribution of noise to a given component of the aircraft. Progress in airframe-noise simulations appears real, but systematic grid-refinement studies and noise comparisons with experiment or other simulations have yet to occur, and the theoretical uncertainty is high.

[1]  F. Harris.  On the use of windows for harmonic analysis with the discrete Fourier transform , 1978, Proceedings of the IEEE.

[2]  Philippe R. Spalart,et al.  Detached-Eddy Simulations Over a Simplified Landing Gear , 2002 .

[3]  S. Crow,et al.  Aerodynamic Sound Emission as a Singular Perturbation Problem , 1970 .

[4]  Fei Li,et al.  Aeroacoustic Analysis of a Simplified Landing Gear , 2003 .

[5]  Andrey Garbaruk,et al.  Further Steps in LES-Based Noise Prediction for Complex Jets , 2006 .

[6]  A. Powell.  Aerodynamic Noise and the Plane Boundary , 1960 .

[7]  F. Farassat,et al.  An Analytical Comparison of the Acoustic Analogy and Kirchhoff Formulation for Moving Surfaces , 1997 .

[8]  Bastien Caruelle,et al.  LAGOON: further analysis of aerodynamic experiments and early aeroacoustics results , 2009 .

[9]  Frank Thiele,et al.  Prediction of sound generated by a rod–airfoil configuration using EASM DES and the generalised Lighthill/FW-H analogy , 2008 .

[10]  Ulf Michel,et al.  Directivity of landing-gear noise based on flyover measurements , 1999 .

[11]  Yueping Guo,et al.  Experimental Study on Aircraft Landing Gear Noise , 2006 .

[12]  Philippe R. Spalart,et al.  LES-based evaluation of a microjet noise reduction concept in static and flight conditions , 2010 .

[13]  Philippe R. Spalart,et al.  Initial RANS and DDES of a Rudimentary Landing Gear , 2010 .

[14]  P. Spalart,et al.  Physical and Numerical Upgrades in the Detached-Eddy Simulation of Complex Turbulent Flows , 2002 .

[15]  N. Curle.  The influence of solid boundaries upon aerodynamic sound , 1955, Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences.

[16]  Barry S. Lazos,et al.  Mean Flow Features Around the Inline Wheels of Four-Wheel Landing Gear , 2002 .

[17]  P. Spalart,et al.  A New Version of Detached-eddy Simulation, Resistant to Ambiguous Grid Densities , 2006 .

[18]  Lakshmi Venkatakrishnan,et al.  Experimental studies on a rudimentary four-wheel landing gear. AIAA 2011-354 , 2011 .

[19]  P. Spalart.  Comments on the feasibility of LES for wings, and on a hybrid RANS/LES approach , 1997 .

[20]  F.J. Souliez,et al.  Landing Gear Aerodynamic Noise Prediction Using Unstructured Grids , 2002 .

[21]  D. G. Crighton,et al.  Basic principles of aerodynamic noise generation , 1975 .

[22]  Wr Graham,et al.  Mechanisms for Model Scale Landing Gear Noise Generation , 2008 .

[23]  Kazuomi Yamamoto,et al.  Aerodynamic and aeroacoustic simulations of a two-wheel landing gear , 2010 .

[24]  Philippe R. Spalart,et al.  Analysis of Experimental and Numerical Studies of the Rudimentary Landing Gear , 2011 .

[25]  P. Spalart,et al.  Noise Prediction for Increasingly Complex Jets. Part I: Methods and Tests , 2005 .

[26]  Ann P. Dowling,et al.  Modern Methods in Analytical Acoustics: Lecture Notes , 1992 .