Experimental Study of Supersonic Jet Noise Reduction With Microjet Injection

Experimental study was conducted concerning active control of supersonic jet noise with a microjet injection technique. The microjets were injected into a rectangular main jet with Mach number up to 1.49. The nozzle lip of the main jet was equipped with 44 injection holes of the microjets, whose angles against the main jet were changed as 60 and 90 degrees. From far-field sound pressure data, a significant reduction of the jet noise by several dB was found in the cases with 60 and 90 degrees of injection angles. The microjet was found to affect all components of supersonic jet noise, namely, turbulent mixing noise, shock-associated broadband noise and screech tone noise. In the results of FFT analysis, the effect of the microjet was observed in the sound pressure level of the shock-associated broadband noise, the pressure level and frequency of the screech tone noise, and average level of the turbulent mixing noise. Schlieren visualization was also made for the jet flow, and the microjet was seen to change the shock structure and shear layer behavior of the supersonic jet.

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An Experimental Study of Shock-Free Supersonic Jet Noise

Aeroacoustics: Jet Noise, Combustion and Core Engine Noise ◽

10.2514/5.9781600865176.0203.0236 ◽

1976 ◽

pp. 203-236

Keyword(s):

Experimental Study ◽

Supersonic Jet ◽

Jet Noise ◽

Supersonic Jet Noise

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Physics and Prediction of Supersonic Jet Noise

Applied Mechanics Reviews ◽

10.1115/1.3124402 ◽

1994 ◽

Vol 47 (6S) ◽

pp. S184-S187

Author(s):

Christopher K. W. Tam

Keyword(s):

Supersonic Jet ◽

Jet Noise ◽

Supersonic Jets ◽

Wave Radiation ◽

Instability Wave ◽

Empirical Constant ◽

Supersonic Jet Noise ◽

Turbulence Structures ◽

Mixing Noise ◽

Dominant Part

Both the large turbulence structures and the fine scale turbulence of the flows of supersonic jets are sources of turbulent mixing noise. At moderately high supersonic Mach numbers especially for hot jets, the dominant part of the noise is generated directly by the large turbulence structures. The large turbulence structures propagate downstream at supersonic velocities relative to the ambient sound speed. They generate strong Mach wave radiation analogous to a supersonically travelling wavy wall. A stochastic instability wave model theory of the large turbulence structures and noise of supersonic jets has recently been developed. The theory can predict both the spectrum and directivity of the dominant part of supersonic jet noise up to a multiplicative empirical constant. Calculated results agree well with measurements.

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Influence of Microjet Injection on Supersonic Jet Noise and Flow Field

Volume 1: Aircraft Engine; Ceramics; Coal, Biomass and Alternative Fuels; Wind Turbine Technology ◽

10.1115/gt2011-46150 ◽

2011 ◽

Cited By ~ 1

Author(s):

Ryuichi Okada ◽

Toshinori Watanabe ◽

Seiji Uzawa ◽

Takehiro Himeno ◽

Tsutomu Oishi

Keyword(s):

Flow Field ◽

Noise Reduction ◽

Sound Pressure ◽

Supersonic Jet ◽

Jet Noise ◽

Cfd Analysis ◽

Jet Engines ◽

Acoustic Measurements ◽

Pressure Data ◽

Supersonic Jet Noise

Jet noise reduction is essential for realization of environmentally-friendly and highly-efficient supersonic jet engines for future civil transport. In the present study, experimental and numerical investigations were conducted to clarify the effect of microjet injection on supersonic jet noise. The experiments were focused on supersonic jet with Mach number up to 1.49 that was generated from a rectangular nozzle with high aspect ratio. Far field acoustic measurements were executed and the spectra and sound pressure data of jet noise were obtained. In order to understand the mechanism of noise reduction, flow field visualization was performed with shadowgraph technique. CFD analysis was conducted as well to observe the flow field and to estimate thrust loss due to the microjet injection.

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Experimental Investigation on Supersonic Jet Noise

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.588-589.860 ◽

2012 ◽

Vol 588-589 ◽

pp. 860-863

Author(s):

Xiao Bo Peng ◽

Jia Ming Li ◽

Chun Bo Hu

Keyword(s):

Mach Number ◽

Sound Production ◽

Supersonic Jet ◽

Jet Noise ◽

Occurrence Frequency ◽

Correlated Noise ◽

Experimental Conditions ◽

Supersonic Jet Noise ◽

Validation Criteria ◽

Mixing Noise

A systematic study has been undertaken to quantify the effects of jet Mach number and nozzle size on the noise radiated by supersonic jets. All the tests were carried out at an experimental bench of the supersonic jet. Results indicate that the field distribution of supersonic jet screech tones is characterized with very strong directivity. Under the textual experimental conditions, if the jet Mach number remain unchanged, the diameter of nozzle throat increases gradually from 5mm to 8mm or 10mm, and the amplitude values of both the turbulent mixing noise and broadband shockwave correlated noise increase by 2-5dB, and the amplitude value change of the whistler type noise is not obvious, and the occurrence frequency of the whistler type noise decreases by more than 2000Hz; if the jet Mach number increases to 3.0 from 2.0, the amplitude value of the whistler type noise increases by more than 2dB, and the occurrence frequency of the whistler type noise decreases obviously. The experimental measurements of supersonic jet noise provide the sound production mechanism research on the supersonic jet noise with data supports and references and provide the numerical modeling of the supersonic jet noise with validation criteria.

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Experimental Study on a Notched Nozzle for Jet Noise Reduction

Volume 1: Aircraft Engine; Ceramics; Coal, Biomass and Alternative Fuels; Wind Turbine Technology ◽

10.1115/gt2011-46244 ◽

2011 ◽

Cited By ~ 4

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.

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