Experimental Studies on Airframe Noise Reduction (original) (raw)

Experimental investigation on the effect of slat geometrical configurations on aerodynamic noise

Journal of Sound and Vibration, 2017

Relatively few studies have addressed the slat noise dependence on gap, overlap and deflection angle, although slat noise level and spectral content are topics of increasing concern in the aeronautical industry. This paper presents new experimental data on the subject. An array of microphones placed in a closed-section wind tunnel was used in the experiments. Beamforming signal processing enhanced by DAMAS (Deconvolution Approach for the Mapping of Acoustic Sources) was applied to the data. The experimental data covered a range of angles of attack and Mach numbers, for which the typical slat noise signature features high-level narrow-band peaks, broadband noise and a single broad tone. The narrow-band peaks often dominate the slat noise spectra and arise at Strouhal numbers up to approximately 5. The broadband noise is well characterized for Strouhal numbers between 5 and 20, whereas the broad tone arises for Strouhal above 20. A total of 10 different slat configurations, including variations in gap, overlap and deflection angle were tested. The slat noise dependence on gap, overlap and slat deflection angle was assessed by letting each of them vary separately. The slat configuration exerted a substantial effect on all slat noise components, with variations of up to 20 dB/Hz in the level of the narrow-band peaks. In general, the level of the narrow-band peaks reduced and the high frequency content increased as the gap, overlap, angle of attack and slat deflection increased separately or in combination. The aerodynamically optimized baseline configuration is very distinct from the lowest noise one.

Parametric analysis of the influence of slat geometry on airframe noise by a commercial code

I am also grateful to Danillo Reis and Eduardo Coelho, who lead the SILENCE Aircraft project, for the technical and operational support. My special acknowledgements to Matheus T. de Araujo and Gil Greco for their assistance with the use of PowerFLOW software and availability to solve my questions, and the computational technical personnel from the Federal University of Santa Catarina for their help with the cluster. Thanks to all the professors I have met during my master's degree program for their technical and personal contributions, which have made me a better professional and researcher. My special gratitude to Prof. PhD. Hernán D. Cerón for his trust in me since I came to Brazil, and for always devoting time to help me, explaining and discussing results, and providing me with his personal support. I am thankful to the LAE laboratory technician and friend Osnán I. Faria for his every day joy and assistance with the construction of the model; his knowledge and experience have surely led to improvements in the results. My acknowledgments to the postgraduate program and aeronautical engineering department secretaries Ana Paula Bueno, Iara Olveira and Gisele Poppy for always being willing to help and for their friendly welcome. I would especially like to thank Angela Giampedro and Elena Palloni for checking this dissertation, and my colleagues of the LAE laboratory for their constant support and for making my days better. Special thanks to Lourenço T. Pereira for his teachings of aerodynamics, aeroacoustics and Matlab, challenges posed, which have made me a better researcher and person, and invaluable assistance. I am thankful to my friends from CEFER USP São Carlos, for their company, friendship, and support, and those from AdS for welcoming me in their group and in their lives. I am also grateful to my Colombian friends in Brazil for being my family in this country. My heartfelt thanks to Daniel Acevedo for his support throughout these 2 years. Last, but not least, I want to thank my family for always pushing me towards achieving my dreams, always supporting my decisions and giving me unconditional love. My gratefulness to my parents, who are my inspiration, Diana Bolívar and Javier Botero, for all their sacrifices for my being here, my siblings, Sara and Franciso Botero, for teaching me love is bigger than anything else in the world, and my goddaughter, Paulina Acevedo, for always waiting for me with open arms and making me feel I am present in her life.

Slat Noise Simulations: Status and Challenges

2011

Noise radiation from the leading edge slat of a high-lift system is known to be an important component of aircraft noise during approach. NASA's Langley Research Center is engaged in a coordinated series of investigations combining high-fidelity numerical simulations and detailed wind tunnel measurements of a generic, unswept, 3-element, high-lift configuration. The goal of this effort is to provide a validated predictive capability that would enable identification of the dominant noise source mechanisms and, ultimately, help develop physics inspired concepts for reducing the far-field acoustic intensity. This paper provides a brief overview of the current status of the computational effort and describes new findings pertaining to the effects of the angle of attack on the aeroacoustics of the slat cove region. Finally, the interplay of the simulation campaign with the concurrently evolving development of a benchmark dataset for an international workshop on airframe noise is outl...

An analysis of slat noise using prediction models

Le Centre pour la Communication Scientifique Directe - HAL - Inria, 2020

In this paper semi-empirical formulas are presented that relate macroscopic flow parameters observed in the slat cove and semi-empirical constants proposed in Guo's semianalytical model. Fourteen slat configurations were simulated using the Lattice Boltzmann Method (LBM) implemented in PowerFLOW R commercial software. These results show an elementary relation between the four semiempirical constants proposed in Guo's slat model and important flow parameters, e.g., the shear-layer path length and the maximum shear velocity. Consequently, those four semi-empirical constants were rewritten in terms of two empirical constants which values can be derived from RANS simulations. The proposed noise prediction model is consequently validated against wind tunnel aeroacoustics tests performed with the 30P30N high-lift device model. Experiments performed in the UTwente Aeroacoustic Wind Tunnel at Re c = 1 • 10 6 and M = 0.15 showed good overall agreement between noise measurements and the proposed slat noise prediction model.

Unsteady Numerical Simulation of Slat Junction Noise

19th AIAA/CEAS Aeroacoustics Conference, 2013

The noise generation from a partially closed slat junction is investigated numerically using a Lattice Boltzmann and Very Large Eddy Simulation (LBM-VLES) methodology. The distinct advantage of LBM over traditional computational fluid dynamics (CFD) methods is in its linear formulaic expression and its ease in handling problems with complex geometries. The slat junction is defined as the gap between two slat segments placed side-by-side. A partially closed slat junction gap is considered. To mimic the effect of the slat junction gap, a three dimensional unswept wing with a three quarter span slat and a half span flap is used in this study. The unswept wing was simulated in a closed section wind tunnel with a freestream Mach number, M 1 D 0:22, and a nominal wing chord Reynolds number, Re c D 3:7 10 6 . Validation of a baseline case show good agreement with experiments for the near-field. The noise and acoustical results however show discrepancies and is attributed to geometrical uncertainties between simulation and experiments. The far-field sound was computed using the impermeable Ffowcs Williams and Hawkings surface integral acoustic method (FW-H). The far-field sound show an overall increase of approximately 2 dB for a partially covered straight and slanted slat junction compared to a baseline slat without a junction.

Analysis of a semi-empirical leading-edge slat noise prediction model

2020

Noise Radiation from a Leading-Edge Slat

15th AIAA/CEAS Aeroacoustics Conference (30th AIAA Aeroacoustics Conference), 2009

This paper extends our previous computations of unsteady flow within the slat cove region of a multi-element high-lift airfoil configuration, which showed that both statistical and structural aspects of the experimentally observed unsteady flow behavior can be captured via 3D simulations over a computational domain of narrow spanwise extent. Although such narrow domain simulation can account for the spanwise decorrelation of the slat cove fluctuations, the resulting database cannot be applied towards acoustic predictions of the slat without invoking additional approximations to synthesize the fluctuation field over the rest of the span. This deficiency is partially alleviated in the present work by increasing the spanwise extent of the computational domain from 37.3% of the slat chord to nearly 226% (i.e., 15% of the model span). The simulation database is used to verify consistency with previous computational results and, then, to develop predictions of the far-field noise radiation in conjunction with a frequency-domain Ffowcs-Williams Hawkings solver.

Slat Noise from an MD30P30N Airfoil at Extreme Angles of Attack

AIAA Journal

This study investigates the slat noise of a two-dimensional scaled, unswept, and untapered MD30P30N high-lift model. The experimental data refer to aeroacoustic and aerodynamic measurements in a closed-section wind tunnel for a wide range of angles of attack (from −6 deg up to the stall; approximately at 18 deg) and Mach numbers between 0.07 and 0.1. Three slat configurations (the original MD30P30N, another with a higher slat deflection, and one with smaller slat gap and overlap) are studied experimentally. The signal processing applied to the acoustic data involves conventional beamforming enhanced by two deconvolution algorithms, namely, DAMAS and CLEAN-SC. An original variation of the beamforming cluster approach that is based on the coherence level among microphone pairs is introduced, and it improves the results obtained by DAMAS. Below −2 deg and above 12 deg angles of attack, the slat noise is very small and mostly below the wind-tunnel background noise for all configurations. Between −2 and 12 deg angles of attack, the slat noise spectra are substantially affected by the slat configuration, although it always contains a dominant low-frequency content, a midfrequency broadband noise, and a single high-frequency broad peak. Within this range, the lower angles of attack display the strongest low-frequency narrowband peaks. In fact, at lower angles of attack, the low-frequency narrowband peaks scale with a Mach power above 10.

Experimental Studies on Airframe Noise Reduction (original) (raw)

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