Experimental study of noise sources and acoustic propagation in a turbofan model

1990 ◽  
Author(s):  
S. LEWY ◽  
S. CANARD-CARUANA ◽  
J. JULLIARD
Keyword(s):  
Experimental Study ◽  
Acoustic Propagation ◽  
Noise Sources

Experimental Study on a Notched Nozzle for Jet Noise Reduction

2011 ◽  
Author(s):  
T. Ishii ◽  
H. Oinuma ◽  
K. Nagai ◽  
N. Tanaka ◽  
Y. Oba ◽  
...  
Keyword(s):  
Experimental Study ◽  
Noise Reduction ◽  
Sound Pressure Level ◽  
Sound Pressure ◽  
Mixing Layer ◽  
Jet Noise ◽  
Computational Prediction ◽  
Pressure Level ◽  
Far Field ◽  
Noise Sources

This paper describes an experimental study on a notched nozzle for jet noise reduction. The notch, a tiny tetrahedral dent formed at the edge of a nozzle, is expected to enhance mixing within a limited region downstream of the nozzle. The enhanced mixing leads to the suppression of broadband peak components of jet noise with little effect on the engine performance. To investigate the noise reduction performances of a six-notch nozzle, a series of experiments have been performed at an outdoor test site. Tests on the engine include acoustic measurement in the far field to evaluate the noise reduction level with and without the notched nozzle, and pressure measurement near the jet plume to obtain information on noise sources. The far-field measurement indicated the noise reduction by as much as 3 dB in terms of overall sound pressure level in the rear direction of the engine. The use of the six-notch nozzle though decreased the noise-benefit in the side direction. Experimental data indicate that the high-frequency components deteriorate the noise reduction performance at wider angles of radiation. Although the increase in noise is partly because of the increase in velocity, the penetration of the notches into the jet plume is attributed to the increase in sound pressure level in higher frequencies. The results of near-field measurement suggest that an additional sound source appears up to x/D = 4 due to the notches. In addition, the total pressure maps downstream of the nozzle edge, obtained using a pressure rake, show that the notched nozzle deforms the shape of the mixing layer, causing it to become wavy within a limited distance from the nozzle. This deformation of the mixing layer implies strong vortex shedding and thus additional noise sources. To improve the noise characteristics, we proposed a revised version of the nozzle on the basis of a computational prediction, which contained 18 notches that were smaller than those in the 6-notched nozzle. Ongoing tests indicate greater noise reduction in agreement with the computational prediction.

scholarly journals Underwater noise in the Slovenian Sea

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Andreja Popit
Keyword(s):  
Wind Speed ◽  
Statistical Methods ◽  
Acoustic Propagation ◽  
Anthropogenic Noise ◽  
Underwater Noise ◽  
Noise Levels ◽  
Marine Strategy Framework Directive ◽  
Noise Sources ◽  
The Eu

Abstract Continuous underwater noise has been monitored in the Slovenian sea near the lighthouse foundation at Debeli Rtič since February 2015, according to the EU Marine Strategy Framework Directive (MSFD). Anthropogenic noise sources (e.g. seawater densities, dredging activities and cleaning of the seafloor) and meteorological noise sources (e.g. wind speed and precipitation) were analysed in relation to the measured underwater noise levels using several graphical and statistical methods. The results of this study showed that average equivalent continuous underwater noise levels were, by 11 dB (L eq,63 Hz) and 5 dB (L eq,125 Hz), higher in the intervals when dredging activities took place than in the intervals when these activities were absent. Variation in underwater noise levels was partly related to the variation of the ship densities, which could be explained by the relatively small acoustic propagation in the shallow seawater. Precipitation level did not indicate any significant association with the variations in continuous underwater noise levels, though some larger deviations in the wind speed were found to be associated with the larger fluctuations in continuous underwater noise levels.

Experimental study and modeling of the white noise sources in submicron Pand N-MOSFETs

2001 ◽  
Vol 48 (4) ◽  
pp. 1577-1586 ◽  
Author(s):  
V. Re ◽  
I. Bietti ◽  
R. Castello ◽  
M. Manghisoni ◽  
V. Speziali ◽  
...  
Keyword(s):  
Experimental Study ◽  
White Noise ◽  
Noise Sources

scholarly journals Experimental study on the acoustic propagation and anisotropy of coal rocks

Petroleum ◽  
2020 ◽  
Author(s):  
Linlin Huang ◽  
Xiangjun Liu ◽  
Sen Yan ◽  
Jian Xiong ◽  
Haiming He ◽  
...  
Keyword(s):  
Experimental Study ◽  
Acoustic Propagation

Aeroacoustic Computations of Contra-Rotating Open Rotors Using the Nonlinear Harmonic Method and a Chorochronic Approach

2012 ◽  
Author(s):  
P.-A. Hoffer ◽  
T. Deconinck ◽  
Ch. Hirsch ◽  
B. Ortun ◽  
S. Canard-Caruana ◽  
...  
Keyword(s):  
High Efficiency ◽  
Near Field ◽  
Three Dimensional ◽  
Flow Simulation ◽  
Acoustic Propagation ◽  
Propulsion System ◽  
Scale Model ◽  
Far Field ◽  
Noise Sources ◽  
Harmonic Method

Due to their great potential for fuel saving, Contra-Rotating Open Rotors (CRORs) receive renewed interest by the airframers and the engine manufacturers. The inherent high efficiency of this propulsion system, however, is potentially offset by the level of noise emitted by the open blades. The acoustic impact on passengers and community may represent a major issue to their environmental acceptance. Fast and robust noise prediction tools are clearly required to support the development of quieter propellers and their integration in future civil aeronautical transport. The most common strategy for noise estimation consists in a two-step approach, based on the Lighthill analogy: unsteady near-field aerodynamic flow simulation to evaluate the noise sources, coupled to a far-field acoustic propagation code. Focus is given here on two structured grid flow solvers employed to investigate a scale-model of a 12×10 pusher CROR. The unsteady aerodynamic three-dimensional flow is indeed computed for typical cruise conditions using both the nonlinear harmonic method (NLH) of FINE™/Turbo software and elsA’s chorochronic technique. The evaluation of the far-field noise based on the aerodynamic fields is then carried out with the KIM code, Onera’s acoustic propagation code based on the Ffowcs-Williams and Hawkings (FW-H) formulation. The obtained results enable an analysis of the complex aerodynamic interactions between the two propellers that generate interaction tones in the acoustic signature of the propulsion system. A comparison in terms of numerical settings, computational costs and flow fields is performed between the two CFD methods, which show an excellent match of the predicted global performance of the propulsion system. Some differences in the predicted acoustic signatures are discussed in the paper.

Sign in / Sign up

Export Citation Format

Share Document