Near-field sound radiation of fan tones from an installed turbofan aero-engine

The flow past 3D rigid cavity is a common structure on the surface of the underwater vehicle. The hydrodynamic noise generated by the structure has attracted considerable attention in recent years. Based on LES-Lighthill equivalent sources method, a 3D cavity is analyzed in this paper, when the Mach number is 0.0048. The hydrodynamic noise and the radiated mechanism of 3D cavity are investigated from the correlation between fluctuating pressure and frequency, the near-field sound pressure intensity, and the propagation directivity. It is found that the hydrodynamic noise is supported by the low frequency range, and fluctuating pressure of the trailing-edge is the largest, which is the main dipole source.

Download Full-text

A study of brake disc modal behaviour during squeal generation using high-speed electronic speckle pattern interferometry and near-field sound pressure measurements

Proceedings of the Institution of Mechanical Engineers Part D Journal of Automobile Engineering ◽

10.1243/0954407001527420 ◽

2000 ◽

Vol 214 (3) ◽

pp. 285-296 ◽

Cited By ~ 15

Author(s):

M Reeves ◽

N Taylor ◽

C Edwards ◽

D Williams ◽

C. H. Buckberry

Keyword(s):

High Speed ◽

Sound Pressure ◽

Surface Deformation ◽

Speckle Pattern ◽

Near Field ◽

Electronic Speckle Pattern Interferometry ◽

Brake Disc ◽

Pressure Measurements ◽

Near Field Sound ◽

Field Sound

The out-of-plane surface vibration of a brake disc during naturally excited squeal has been investigated using a combination of high-speed electronic speckle pattern interferometry (ESPI) and near-field sound pressure measurements. Both techniques provide visualization and quantification of the time-resolved surface velocity. A mathematical description of disc brake squeal modal behaviour is proposed that predicts accurately all of the experimentally observed interferometry and sound field measurements. The complex mode description proposed here is in agreement with that proposed by others for drum brake squeal. This assumes that two identical diametral modes are excited simultaneously, identical except for a spatial and temporal phase shift. The use of a near-field microphone array provided a convenient multipoint, non-contacting vibration probe which may find use in the study of other vibrations characterized by high surface amplitudes and efficient sound radiation. The high-speed ESPI provided a real-time visualization of surface deformation analogous to double- pulsed holographic interferometry, with the benefit of giving a true time series of the surface deformation during a single vibration cycle.

Download Full-text

An Experimental Investigation on the Bridge Effect in Sound Produced by Setar

Volume 15: Sound, Vibration and Design ◽

10.1115/imece2009-13048 ◽

2009 ◽

Author(s):

Hossein Mansour ◽

Siamak Arzanpour ◽

Hedayat Alghassi ◽

Mehdi Behzad

Keyword(s):

Experimental Investigation ◽

Near Field ◽

Musical Instruments ◽

Minor Effect ◽

The Third ◽

Vibrating System ◽

Novel Approach ◽

Energy Transfers ◽

Near Field Sound ◽

Field Sound

This study aims to evaluate the amount of energy transfers through the bridge in Setar, a Persian long-necked lute. Stringed musical instruments are among the most complicated acoustical systems. When the string is plucked, its vibration distributes into the entire vibrating system (i.e. body, string, air enclosure) and produces sound. The resultant sound consists of three parts: the first is the string’s direct sound; the second is that part of sound-box vibration being excited by string’s direct sound, and the third is the part of sound-box vibration being excited by string force passing through bridge. The last part believed to have the major share and the others have minor effect. For this research, a specific fixture has been made and a precise plucking machine is installed to hold and pluck the instrument uniformly. Also, a novel approach is utilized to evaluate the share of each abovementioned part in the output near-field sound produced by Setar.

Download Full-text