On the Limitations of High Speed Jet Noise Suppression (Keynote Paper)

2003 ◽  
Author(s):  
Anjaneyuly Krothapalli ◽  
Brenton Greska ◽  
Vijay Arakeri
Keyword(s):  
High Speed ◽  
Noise Suppression ◽  
Jet Noise ◽  
Current Data ◽  
Wave Radiation ◽  
Far Field ◽  
Noise Sources ◽  
Turbulence Suppression ◽  
Mixing Noise ◽  
Large Eddies

This paper deals with an experimental investigation on the suppression of high-speed jet noise using air/water microjet injection at the nozzle exit. The far-field acoustic measurements from a high temperature Mj = 1.38 and Mj = 0.9 axisymmetric jet issuing from a converging nozzle show the suppression of screech tones, Mach wave radiation/crackle and mixing noise due to the use of microjets. Estimations of the contributions of different noise sources to the far-field sound are made using the current data supported by observations of previous investigators. It appears that the mixing noise reduction due to elimination of large eddies is found to be about 3–5 dB. Any further reduction of noise may only be accomplished by significant turbulence suppression and thermodynamic changes in the jet.

Simultaneous Noise and Performance Measurements for High-Speed Jet Noise Reduction Technologies

2009 ◽  
Author(s):  
Dean Long ◽  
Steven Martens
Keyword(s):  
Noise Reduction ◽  
High Speed ◽  
Near Field ◽  
Jet Noise ◽  
Source Distribution ◽  
Test Facility ◽  
Wave Radiation ◽  
Far Field ◽  
Shock Cell ◽  
Field Noise

Model scale tests are conducted to assess the Noise/Performance trade for high speed jet noise reduction technologies. It is demonstrated that measuring the near field acoustic signature with a microphone array can be used to assess the far field noise using a procedure known as acoustic holography. The near field noise measurement is mathematically propagated producing an estimate of the noise level at the new location. Outward propagation produces an estimate of the far field noise. Propagation toward the jet axis produces the source distribution. Tests are conducted on convergent/divergent nozzles with three different area ratios, and several different chevron geometries. Noise is characterized by two independent processes: Shock cell noise radiating in the forward quadrant is produced when the nozzle is operated at non-ideally expanded conditions. Mach wave radiation propagates into the aft quadrant when the exhaust temperature is elevated. These results show good agreement with actual far field measurements from tests in the GE Cell 41 Acoustic Test Facility. Simultaneous performance measurement shows the change in thrust coefficient for different test conditions and configurations. Chevrons attached to the nozzle exit can reduce the noise by several dB at the expense of a minimal thrust loss.

scholarly journals The sources of jet noise: experimental evidence

2008 ◽  
Vol 615 ◽  
pp. 253-292 ◽  
Author(s):  
CHRISTOPHER K. W. TAM ◽  
K. VISWANATHAN ◽  
K. K. AHUJA ◽  
J. PANDA
Keyword(s):  
High Speed ◽  
Noise Source ◽  
Jet Noise ◽  
Polar Angle ◽  
Sound Field ◽  
Source Distribution ◽  
Far Field ◽  
Noise Sources ◽  
Directional Information ◽  
Jet Mixing

The primary objective of this investigation is to determine experimentally the sources of jet mixing noise. In the present study, four different approaches are used. It is reasonable to assume that the characteristics of the noise sources are imprinted on their radiation fields. Under this assumption, it becomes possible to analyse the characteristics of the far-field sound and then infer back to the characteristics of the sources. The first approach is to make use of the spectral and directional information measured by a single microphone in the far field. A detailed analysis of a large collection of far-field noise data has been carried out. The purpose is to identify special characteristics that can be linked directly to those of the sources. The second approach is to measure the coherence of the sound field using two microphones. The autocorrelations and cross-correlations of these measurements offer not only valuable information on the spatial structure of the noise field in the radial and polar angle directions, but also on the sources inside the jet. The third approach involves measuring the correlation between turbulence fluctuations inside a jet and the radiated noise in the far field. This is the most direct and unambiguous way of identifying the sources of jet noise. In the fourth approach, a mirror microphone is used to measure the noise source distribution along the lengths of high-speed jets. Features and trends observed in noise source strength distributions are expected to shed light on the source mechanisms. It will be shown that all four types of data indicate clearly the existence of two distinct noise sources in jets. One source of noise is the fine-scale turbulence and the other source is the large turbulence structures of the jet flow. Some of the salient features of the sound field associated with the two noise sources are reported in this paper.

Simultaneous Noise and Performance Measurements for High Speed Jet Noise Reduction Technologies: Part II—Near Field Array Calibration

2011 ◽  
Author(s):  
Dean Long ◽  
Steve Martens
Keyword(s):  
Noise Reduction ◽  
High Speed ◽  
Near Field ◽  
Jet Noise ◽  
Source Distribution ◽  
Wave Radiation ◽  
Far Field ◽  
Performance Measurements ◽  
Shock Cell ◽  
Field Noise

Part I of this paper describes a methodology for assessing the far field jet noise from high speed exhaust nozzles using a microphone array in the near field of the exhaust plume. The near field noise measurement is mathematically propagated producing an estimate of the noise level at the new location. Outward propagation produces an estimate of the far field noise. Propagation toward the jet axis produces the source distribution. Part II described here provides a direct validation of this process using a generic CD nozzle in a facility where both the near field and the far field are measured simultaneously. Comparison of these data sets show good agreement over the typical operating range for this type of nozzle. The far field noise is characterized by two independent processes: Shock cell noise radiating in the forward quadrant is produced when the nozzle is operated at non-ideally expanded conditions. Mach wave radiation propagates into the aft quadrant when the exhaust temperature is elevated. Subsequent tests in an acoustically treated nozzle thrust stand demonstrate the value of the near field array allowing immediate feedback on the noise/performance tradeoff for high speed jet noise reduction technologies.

Turbulence suppression in free turbulent shear flows under controlled excitation. Part 2. Jet-noise reduction

1985 ◽  
Vol 150 ◽  
pp. 159-168 ◽  
Author(s):  
A. K. M. F. Hussain ◽  
M. A. Z. Hasan
Keyword(s):  
Shear Layer ◽  
Noise Suppression ◽  
Jet Noise ◽  
Direct Consequence ◽  
Turbulent Shear ◽  
Far Field ◽  
Momentum Thickness ◽  
Hot Wire ◽  
Turbulence Suppression ◽  
Instability Modes

It is shown that reduction of broadband (even total) far-field jet noise can be achieved via controlled excitation of a jet at a frequency in the range 0.01 < Stθ < 0.02, where Stθ is the Strouhal number based on the exit momentum thickness of the shear layer. Hot-wire measurements in the noise-producing region of the jet reveal that the noise suppression is a direct consequence of turbulence suppression, produced by early saturation and breakdown of maximally growing instability modes.

On the Far-Field Propagation of High-Speed Jet Noise

2008 ◽  
Author(s):  
Brenton Greska ◽  
Anjaneyulu Krothapalli
Keyword(s):  
Nozzle Exit ◽  
High Speed ◽  
Jet Noise ◽  
Wave Radiation ◽  
Far Field ◽  
Radial Line ◽  
Experimental Conditions ◽  
Atmospheric Absorption ◽  
The Common ◽  
Radiation Direction

This paper deals with the effects of atmospheric absorption on the propagation of high-speed jet noise. The common practice for determining the far-field jet noise spectra at a distance far from the jet exit (>100D, where D is the nozzle exit diameter) involves extrapolating data that is typically obtained between 35D and 100D from the nozzle exit. The data is extrapolated along a radial line from the nozzle exit by accounting for the effects of spherical spreading and atmospheric absorption. A previous paper discussed far-field measurements that were obtained for a twin engine aircraft at three locations along a radial line in the peak noise radiation direction. The authors were unable to extrapolate the spectra from the nearest location to either of the further locations and the observed differences were attributed to nonlinear effects in the jet noise signal. It is the purpose of this paper to show that the common extrapolation practice is valid for high speed jets, except in the peak radiation direction and its surrounding angles. Mach wave radiation is present at these locations and the common practice will yield unsatisfactory results, similar to those observed in the previous paper. The data used in this paper is taken from experiments carried out at 1/5th-scale and full scale and the experimental conditions of these high-speed jets are quite similar to those of the previous paper.

scholarly journals Jet-Surface Interaction Test: Far-Field Noise Results

2013 ◽  
Vol 135 (7) ◽  
Author(s):  
Clifford A. Brown
Keyword(s):  
High Speed ◽  
Radial Distance ◽  
Jet Noise ◽  
Surface Interaction ◽  
Shielding Effect ◽  
Noise Prediction ◽  
Far Field ◽  
Wide Range ◽  
Field Noise ◽  
Surface Length

Many configurations proposed for the next generation of aircraft rely on the wing or other aircraft surfaces to shield the engine noise from the observers on the ground. However, the ability to predict the shielding effect and any new noise sources that arise from the high-speed jet flow interacting with a hard surface is currently limited. Furthermore, quality experimental data from jets with surfaces nearby suitable for developing and validating noise prediction methods are usually tied to a particular vehicle concept and, therefore, very complicated. The Jet-Surface Interaction Tests are intended to supply a high quality set of data covering a wide range of surface geometries and positions and jet flows to researchers developing aircraft noise prediction tools. The initial goal is to measure the noise of a jet near a simple planar surface while varying the surface length and location in order to: (1) validate noise prediction schemes when the surface is acting only as a jet noise shield and when the jet-surface interaction is creating additional noise, and (2) determine regions of interest for future, more detailed, tests. To meet these objectives, a flat plate was mounted on a two-axis traverse in two distinct configurations: (1) as a shield between the jet and the observer and (2) as a reflecting surface on the opposite side of the jet from the observer. The surface length was varied between 2 and 20 jet diameters downstream of the nozzle exit. Similarly, the radial distance from the jet centerline to the surface face was varied between 1 and 16 jet diameters. Far-field and phased array noise data were acquired at each combination of surface length and radial location using two nozzles operating at jet exit conditions across several flow regimes: subsonic cold, subsonic hot, underexpanded, ideally expanded, and overexpanded supersonic. The far-field noise results, discussed here, show where the jet noise is partially shielded by the surface and where jet-surface interaction noise dominates the low frequency spectrum as a surface extends downstream and approaches the jet plume.

scholarly journals Jet-Surface Interaction Test: Phased Array Noise Source Localization Results

2012 ◽  
Author(s):  
Gary G. Podboy
Keyword(s):  
Source Localization ◽  
Phased Array ◽  
Noise Source ◽  
Jet Noise ◽  
Companion Paper ◽  
Far Field ◽  
Sound Waves ◽  
Axial Distribution ◽  
Noise Sources ◽  
Interaction Test

An experiment was conducted to investigate the effect that a planar surface located near a jet flow has on the noise radiated to the far-field. Two different configurations were tested: 1) a shielding configuration in which the surface was located between the jet and the far-field microphones, and 2) a reflecting configuration in which the surface was mounted on the opposite side of the jet, and thus the jet noise was free to reflect off the surface toward the microphones. Both conventional far-field microphone and phased array noise source localization measurements were obtained. This paper discusses phased array results, while a companion paper discusses far-field results. The phased array data show that the axial distribution of noise sources in a jet can vary greatly depending on the jet operating condition and suggests that it would first be necessary to know or be able to predict this distribution in order to be able to predict the amount of noise reduction to expect from a given shielding configuration. The data obtained on both subsonic and supersonic jets show that the noise sources associated with a given frequency of noise tend to move downstream, and therefore, would become more difficult to shield, as jet Mach number increases. The noise source localization data obtained on cold, shock-containing jets suggests that the constructive interference of sound waves that produces noise at a given frequency within a broadband shock noise hump comes primarily from a small number of shocks, rather than from all the shocks at the same time. The reflecting configuration data illustrates that the law of reflection must be satisfied in order for jet noise to reflect off of a surface to an observer, and depending on the relative locations of the jet, the surface, and the observer, only some of the jet noise sources may satisfy this requirement.

Physics and Prediction of Supersonic Jet Noise

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.

Sign in / Sign up

Export Citation Format

Share Document