Study of Jet Noise Reduction on Separated Exhaust System Using Chevron Nozzles

2014 ◽  
Vol 1078 ◽  
pp. 228-234
Author(s):  
Wan Ren Shao ◽  
Xi Hai Xu ◽  
Jing Yu He ◽  
Fei Wu
Keyword(s):  
Noise Reduction ◽  
Jet Noise ◽  
Exhaust System ◽  
Scale Model ◽  
Low Frequencies ◽  
Chevron Nozzles ◽  
Field Noise ◽  
Bypass Ratio ◽  
Computational Predictions ◽  
Noise Spectra

The jet noise reduction of chevron nozzles was investigated on high bypass ratio turbofan engine separated exhaust system using both computational predictions and scale model experiments. Six different exhaust nozzles are designed including one baseline nozzle and five different chevron nozzles. The jet noise experiments were carried out in the anechoic chamber. Tam and Auriault’s jet noise prediction theory and MGBK theory were used to predict the noise spectra of different exhaust nozzles. The results show that the far-field noise spectra as well as the noise reduction benefits of chevrons are predicted correctly by the two theories although some discrepancies occur at the high frequency range, and Tam and Auriault’s jet noise theory can give relatively more accurate prediction results. chevron nozzles reduce jet noise at the low frequencies, but increase it at high frequencies.

scholarly journals Exo-Skeletal Engine: Novel Engine Concept

2003 ◽  
Author(s):  
Christos C. Chamis ◽  
Isaiah M. Blankson
Keyword(s):  
Noise Reduction ◽  
Open Channel ◽  
Jet Noise ◽  
Element Model ◽  
Combined Cycle ◽  
Engine Design ◽  
Potential Benefits ◽  
Immense Potential ◽  
Bypass Ratio ◽  
Engine Concept

The Exo-Skeletal Engine concept represents a new radical engine technology with the potential for a substantial revolution in engine design. It is an all composite drum rotor engine in which conventional heavy shafts and discs are eliminated and are replaced by rotating casings that support the blades in spanwise compression. Thus the rotating blades are in compression rather than in tension. The resulting open channel at the engine centerline has immense potential for jet noise reduction, and can also accommodate an inner combined-cycle thruster such as a ramjet. The Exo-Skeletal Engine is described in some detail with respect to geometry, components and potential benefits. Initial evaluation, results for drum rotors, bearings and weights are summarized. Component configuration, assembly plan and potential fabrication processes are also identified. A finite element model of the assembled engine and its major components are described. Preliminary results obtained thus far show at least 30 percent reduction of engine weight and about 10 db noise reduction, compared to a baseline conventional high bypass-ratio engine. Potential benefits in all aspects of engine technology are identified and tabulated. Quantitative assessments of potential benefits are in progress.

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 Modelling installed jet noise due to the scattering of jet instability waves by swept wings

2019 ◽  
Vol 870 ◽  
pp. 760-783 ◽  
Author(s):  
Benshuai Lyu ◽  
Ann P. Dowling
Keyword(s):  
Noise Reduction ◽  
Physical Mechanism ◽  
Jet Noise ◽  
Destructive Interference ◽  
Sweep Angle ◽  
Low Frequencies ◽  
Instability Waves ◽  
Jet Instability ◽  
Reduction Strategies ◽  
Swept Wings

Jet noise is a significant contributor to aircraft noise, and on modern aircraft it is considerably enhanced at low frequencies by a closely installed wing. Recent research has shown that this noise increase is due to the scattering of jet instability waves by the trailing edge of the wing. Experimentalists have recently shown that noise can be reduced by using wings with swept trailing edges. To understand this mechanism, in this paper, we develop an analytical model to predict the installed jet noise due to the scattering of instability waves by a swept wing. The model is based on the Schwarzschild method and Amiet’s approach is used to obtain the far-field sound. The model can correctly predict both the reduction in installed jet noise and the change to directivity patterns observed in experiments due to the use of swept wings. The agreement between the model and experiment is very good, especially for the directivity at large azimuthal angles. It is found that the principal physical mechanism of sound reduction is due to destructive interference. It is concluded that in order to obtain an effective noise reduction, both the span and the sweep angle of the wing have to be large. Such a model can greatly aid in the design of quieter swept wings and the physical mechanism identified can provide significant insight into developing other innovative noise-reduction strategies.

Analysis of Jet-Noise-Reduction Concepts by Large-Eddy Simulation

2007 ◽  
Vol 6 (3) ◽  
pp. 243-285 ◽  
Author(s):  
Michael L. Shur ◽  
Philippe R. Spalart ◽  
Michael Kh. Strelets ◽  
Andrey V. Garbaruk
Keyword(s):  
Noise Reduction ◽  
Low Cost ◽  
Jet Noise ◽  
Physical Models ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Chevron Nozzles ◽  
Automatic Activation ◽  
Computational Resources ◽  
Flux Limiters

The paper outlines the latest improvements to a CFD/CAA numerical system developed by the authors starting in 2001, and presents its application to the evaluation of three noise-reduction concepts. The improvements include a two-step RANS-LES approach to represent complex nozzles much more faithfully, and an accurate algorithm for shock capturing in LES, now based on local automatic activation of flux-limiters. The noise-reduction concepts considered are: beveled nozzles, dual nozzles with fan-flow deflection, and chevron nozzles. The simulations are carried out on PC clusters with at most six processors and on rather modest grids (2–4 million nodes). Nonetheless, in most cases the system is close to the 2–3 dB target accuracy both in terms of directivity and spectrum, while limited in terms of frequency (to a diameter Strouhal number that ranges from 2 to 4, depending on the grid used and the flow regime). Although this limitation is significant, especially for chevron nozzles, the overall message of the paper is that the available CFD/CAA numerical and physical models, properly combined, are capable of predicting the noise of rather complex jets with affordable computational resources, and already today can be helpful in the rapid low-cost analysis of noise-reduction concepts.

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.

scholarly journals Impact of Using Chevrons Nozzle on the Acoustics and Performances of a Micro Turbojet Engine

2021 ◽  
Vol 11 (11) ◽  
pp. 5158
Author(s):  
Grigore Cican ◽  
Marius Deaconu ◽  
Daniel-Eugeniu Crunteanu
Keyword(s):  
Noise Reduction ◽  
Compression Ratio ◽  
Test Bench ◽  
Jet Noise ◽  
Equivalent Diameter ◽  
Normal Functioning ◽  
Fuel Flow ◽  
Turbojet Engine ◽  
Propulsion Force ◽  
Chevron Nozzles

This paper presents a study regarding the noise reduction of the turbojet engine, in particular the jet noise of a micro turbojet engine. The results of the measurement campaign are presented followed by a performances analysis which is based on the measured data by the test bench. Within the tests, beside the baseline nozzle other two nozzles with chevrons were tested and evaluated. First type of nozzle is foreseen with eight triangular chevrons, the length of the chevrons being L = 10 percentages from the equivalent diameter and an immersion angle of I = 0 deg. For the second nozzle the length and the immersion angle were maintained, only the chevrons number were increased at 16. The micro turbojet engine has been tested at four different regimes of speed. The engine performances were monitored by measuring the fuel flow, the temperature in front of the turbine, the intake air flow, the compression ratio, the propulsion force and the temperature before the compressor. In addition, during the testing, the vibrations were measured on axial and radial direction which indicate a normal functioning of the engine during the chevron nozzles testing. Regarding the noise, it was concluded that at low regimes the noise doesn’t presents any reduction when using the chevron nozzles, while at high regimes an overall noise reduction of 2–3 dB(A) was achieved. Regarding the engine performances, a decrease in the temperature in front of the turbine, compression ratio and the intake air and fuel flow was achieved and also a drop of few percent of the propulsion force.

scholarly journals Design and evaluating efficiency of gas exhaust system silencer of outboard motor SEA PRO 2.5

2021 ◽  
Vol 2021 (1) ◽  
pp. 81-87
Author(s):  
Mikhail Nikolaevich Pokusaev ◽  
Konstantin Evgenievich Khmelnitsky ◽  
Alexei Alekseevich Kadin ◽  
Alexei Viktorovich Sergeev
Keyword(s):  
Noise Reduction ◽  
Noise Level ◽  
Aerodynamic Drag ◽  
Exhaust System ◽  
Water Layer ◽  
Sound Level ◽  
Low Frequencies ◽  
Full Speed ◽  
Made In China ◽  
Exhaust Systems

The article presents the results of developing and evaluating the effectiveness of the silencer of outboard motor SEA PRO 2.5 made in China. The experiments were carried out in a large experimental pool of Astrakhan State Technical University, with the use of a noise meter-spectrum analyzer Ecophysics-110 of the first class, with the software Signal+3G Light. In the theoretical analysis of the development, it has been suggested that the efficiency of silencers of exhaust systems of outboard motors could have a smaller effect than with cars, since at underwater exhaust the noise reduction will occur from the water layer when the motor is submerged. It has been proved that using a silencer in underwater exhaust systems of outboard motors can increase the aerodynamic drag for gases and reduce power. To test the theoretical assumptions, there was made a silencer for the gas exhaust system of the outboard motor SEA PRO 2.5 from stainless steel perforated sponge. It was determined that the net effect of the silencer (excluding water silencing) could be heard at low frequencies (up to 125 Hz) and makes up to 12.7 dba at full speed of the motor. The average equivalent sound level is reduced up to 4.5 dba at low speed, and at full speed of the outboard motor is practically not evident. In addition, the outboard motor noise level was reduced by water and made at full speed up to 22 dba for frequencies over 2000 Hz; for average equivalent noise level it made 15 dba. The combination of noise reduction by water and by a silencer helps to reduce noise at low and high sound frequencies, which is a positive effect of the developed device.

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