Experiment on engine sound propagation path using a compact microphone array

One of the greatest challenges in modern aircraft propulsion design is the reduction of the engine noise emission in order to develop quieter aircrafts. In the course of a current research project, the sound transport in low pressure turbines is investigated. For the corresponding experimental measurements, a specific acoustic excitation system is developed which can be implemented into the inlet of a turbine test rig and into an aeroacoustic wind tunnel. This allows for an acoustic mode generation and a synthesis of various sound source patterns to simulate typical turbomachinery noise sources such as rotor-stator interaction, etc. The paper presents the acoustical and technical design methodology in detail and addresses the experimental options of the system. Particular attention is paid to the design and the numerical optimization of the acoustic excitation units. To validate the sound generator during operation, measurements are performed in an aeroacoustic wind tunnel. For this purpose, an in-duct microphone array with a specific beamforming algorithm for hard-walled ducts is developed and applied to identify the source locations. The synthetically excited sound fields and the propagating acoustic modes are measured and analyzed by means of modal decomposition techniques. The measurement principles and the results are discussed in detail and it is shown that the intended sound source is produced and the intended sound field is excited. This paper shall contribute to help guide the development of excitation systems for aeroacoustic experiments to better understanding the physics of sound propagation within turbomachines.

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Effect on Sound Source Drift Caused by Angles Between Jet Flow Direction and Microphone Array or Sound Source Plane

Volume 13: Acoustics, Vibration, and Wave Propagation ◽

10.1115/imece2016-66099 ◽

2016 ◽

Author(s):

Zhe Shen ◽

Yigang Wang ◽

Zhigang Yang

Keyword(s):

Wind Tunnel ◽

Sound Source ◽

Sound Propagation ◽

Microphone Array ◽

Flow Direction ◽

Engineering Application ◽

Jet Flow ◽

Source Plane ◽

Geometrical Acoustics ◽

Beamforming Algorithm

When sound generated in jet flow propagates to outside of flow field, direction of sound propagation changes because of wave convection and refraction of shear layer. In wind tunnel, sound source drift appears when sound source is located with out-flow microphone array based on beamforming algorithm. In some cases, angles between jet flow direction and microphone array or sound source plane are inevitable due to geometric position, which increases the number of parameters affecting sound source drift distance. Geometrical acoustics and basic beamforming algorithm were used in this paper to deduce the relation between sound source drift and the angles. Equations for drift prediction and method for error reduction were given. Experimental verification was completed in a full-scale aero-acoustic wind tunnel with 2 loudspeakers set on an auto-body surface and microphone array with 120 channels. The experimental results prove that the equations for sound drift prediction in complicated geometric position relationship have a high accuracy, could help quick locating sound sources in engineering application.

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An Acoustic Excitation System for the Generation of Turbomachinery Specific Sound Fields: Part I — Design and Methodology

Volume 2A: Turbomachinery ◽

10.1115/gt2016-56020 ◽

2016 ◽

Cited By ~ 2

Author(s):

Akif Mumcu ◽

Christian Keller ◽

C. Mandanna Hurfar ◽

Joerg R. Seume

Keyword(s):

Sound Propagation ◽

Microphone Array ◽

Sound Field ◽

Radial Mode ◽

Mode Analysis ◽

Acoustic Excitation ◽

Axial Distribution ◽

Excitation System ◽

Sound Fields ◽

Duct Wall

A strong focus in the development of modern aircraft engines is the reduction of the engine tonal core noise. For the development of efficient noise reduction techniques, a detailed understanding of the sound transmission throughout all turbomachinery components of the engine is mandatory. In this paper an excitation system is developed to generate turbomachinery-specific sound fields by controlling their circumferential and radial mode order. The excitation system consists of two rows of eight loudspeakers distributed circumferentially around the outer duct wall. This paper gives a detailed description of the analytically- and numerically-supported design methodology of an optimized excitation system, as well as an optimized microphone array mounted flush with the outer duct wall. A sensitivity analysis of the loudspeaker array and of the microphone array with respect to distance and frequency is then carried out numerically. To analyze the microphone signals and to deconstruct the propagating sound field into its modal components, a Radial Mode Analysis (RMA) is carried out. To ensure high-quality RMA results, the axial distribution of the microphones is optimized with respect to the condition number of the array’s transfer matrix. The procedure explained in this paper shall help guide the development of acoustic excitation and microphone array systems for experiments to better understand sound propagation in turbomachinery and flow ducts.

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Directional acoustic radiation in the strut display of male sage grouse Centrocercus urophasianus

Journal of Experimental Biology ◽

10.1242/jeb.202.21.2893 ◽

1999 ◽

Vol 202 (21) ◽

pp. 2893-2909 ◽

Cited By ~ 2

Author(s):

M.S. Dantzker ◽

G.B. Deane ◽

J.W. Bradbury

Keyword(s):

Sound Propagation ◽

Acoustic Radiation ◽

Microphone Array ◽

Field Measurements ◽

Centrocercus Urophasianus ◽

Small Scale ◽

Sage Grouse ◽

Radiation Beam ◽

Acoustic Localization ◽

In The Wild

We present evidence that the acoustic component of the strut display of male sage grouse Centrocercus urophasianus is highly directional and that the nature of this directionality is unique among measured vertebrates. Where vertebrate acoustic signals have been found to be directional, they are most intense anteriorly and are bilaterally symmetrical. Our results show that sage grouse acoustic radiation (beam) patterns are often asymmetric about the birds' anterior-posterior axis. The beam pattern of the ‘whistle’ note is actually strikingly bilobate with a deep null directly in front of the displaying bird. While the sage grouse display serves to attract potential mates, male sage grouse rarely face females head on when they call. The results of this study suggest that males may reach females with a high-intensity signal despite their preference for an oblique display posture relative to those females. We characterized these patterns using a novel technique that allowed us to map acoustic radiation patterns of unrestrained animals calling in the wild. Using an eight-microphone array, our technique integrates acoustic localization with synchronous pressure-field measurements while controlling for small-scale environmental variation in sound propagation.

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