Directional Noise Reduction via Asymmetric Downstream Fluidic Injection

2017 ◽  
Author(s):  
Pankaj Rajput ◽  
Sunil Kumar
Keyword(s):  
Noise Reduction ◽  
Turbulent Mixing ◽  
Near Field ◽  
Acoustic Energy ◽  
Far Field ◽  
High Momentum ◽  
Mean Flow ◽  
Flow Measurements ◽  
Mixing Noise ◽  
Field Noise

The main aim of this investigation is to analyze directional noise reduction resulting from asymmetric high momentum fluidic injection downstream of a Mach 0.9 nozzle. Jet noise has been identified as one of the primary obstacles to increasing commercial aviation capacity. Microjets in cross flow are known to enhance turbulent mixing in the shear layer due to the induced stream-wise vortices. This enhanced mixing can be used for reorganizing the spatial distribution of acoustic energy. Targeted reduction in the downward-emitted turbulent mixing noise can be achieved by strategically injecting high momentum fluid downstream of the jet exhaust. Detailed Large Eddy Simulations were performed on a hybrid block structured-unstructured mesh to generate the flow field which was then used for near field and far field noise computation. Aeroacoustic analogy based formulation was used for computing far-field noise estimation. Benchmark cases were validated with preexisting experimental data sets. Mean flow measurements suggest shorter jet core lengths due to the enhanced mixing resulting from fluidic injection. The induced asymmetry due to the fluidic injection gives rise to an asymmetric acoustic field leading to targeted directional noise reduction in the far field as measured by pressure probes.

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.

Surface pressure fluctuations on aircraft flaps and their correlation with far-field noise

2000 ◽  
Vol 415 ◽  
pp. 175-202 ◽  
Author(s):  
Y. P. GUO ◽  
M. C. JOSHI ◽  
P. H. BENT ◽  
K. J. YAMAMOTO
Keyword(s):  
Surface Pressure ◽  
Near Field ◽  
Pressure Fluctuations ◽  
Dominant Frequency ◽  
Vortex Structures ◽  
Far Field ◽  
Mean Flow ◽  
Noise Sources ◽  
Side Edge ◽  
Field Noise

This paper discusses unsteady surface pressures on aircraft flaps and their correlation with far-field noise. Analyses are made of data from a 4.7% DC-10 aircraft model test, conducted in the 40 × 80 feet wind tunnel at NASA Ames Research Center. Results for various slat/wing/flap configurations and various flow conditions are discussed in detail to reveal major trends in surface pressure fluctuations. Spectral analysis, including cross-correlation/coherence, both among unsteady surface pressures and between far-field noise and near-field fluctuations, is used to reveal the most coherent motions in the near field and identify potential sources of noise related to flap flows. Dependencies of surface pressure fluctuations on mean flow Mach numbers, flap settings and slat angles are discussed. Dominant flow features in flap side edge regions, such as the formation of double-vortex structures, are shown to manifest themselves in the unsteady surface pressures as a series of spectral humps. The spectral humps are shown to correlate well with the radiated noise, indicating the existence of major noise sources in flap side edge regions. Strouhal number scaling is used to collapse the data with satisfactory results. The effects of flap side edge fences on surface pressures are also discussed. It is shown that the application of fences effectively increases the thickness of the flaps so that the double-vortex structures have more time to evolve. As a result, the characteristic timescale of the unsteady sources increases, which in turn leads to a decrease in the dominant frequency of the source process. Based on this, an explanation is proposed for the noise reduction mechanism of flap side edge fences.

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 An analytical and experimental investigation of aerofoil–turbulence interaction noise for plates with spanwise-varying leading edges

2019 ◽  
Vol 865 ◽  
pp. 137-168 ◽  
Author(s):  
Lorna J. Ayton ◽  
Paruchuri Chaitanya
Keyword(s):  
Noise Reduction ◽  
Analytic Solution ◽  
Piecewise Linear ◽  
Separation Of Variables ◽  
Leading Edge ◽  
Test Case ◽  
Far Field ◽  
Mean Flow ◽  
Flat Plates ◽  
Leading Edges

This paper presents an analytic solution for gust–aerofoil interaction noise for flat plates with spanwise-varying periodic leading edges in uniform mean flow. The solution is obtained by solving the linear inviscid equations via separation of variables and the Wiener–Hopf technique, and is suitable for calculating the far-field noise generated by any leading edge with a single-valued piecewise linear periodic spanwise geometry. Acoustic results for homogeneous isotropic turbulent flow are calculated by integrating the single-gust solution over a wavenumber spectrum. The far-sound pressure level is calculated for five test-case geometries; sawtooth serration, slitted $v$-root, slitted $u$-root, chopped peak and square wave, and compared to experimental measurements. Good agreement is seen over a range of frequencies and tip-to-root ratios (varying the sharpness of the serration). The analytic solution is then used to calculate the propagating pressure along the leading edge of the serration for fixed spanwise wavenumbers, i.e. only the contribution to the surface pressure which propagates to the far field. Using these results, two primary mechanisms for noise reduction are discussed; tip and root interference, and a redistribution of energy from cuton modes to cutoff modes. A secondary noise-reduction mechanism due to nonlinear features is also discussed and seen to be particularly important for leading edges with very narrow slits.

PREDICTION OF NOISE GENERATED BY A ROUND NOZZLE JET FLOW USING COMPUTATIONAL AEROACOUSTICS

2011 ◽  
Vol 19 (03) ◽  
pp. 291-316 ◽  
Author(s):  
ALI UZUN ◽  
M. YOUSUFF HUSSAINI
Keyword(s):  
Flow Field ◽  
Near Field ◽  
Internal Flow ◽  
Jet Flow ◽  
Computational Aeroacoustics ◽  
Far Field ◽  
Free Jet ◽  
Grid Points ◽  
Field Noise ◽  
Inflow Conditions

This paper demonstrates an application of computational aeroacoustics to the prediction of noise generated by a round nozzle jet flow. In this study, the nozzle internal flow and the free jet flow outside are computed simultaneously by a high-order accurate, multi-block, large-eddy simulation (LES) code with overset grid capability. To simulate the jet flow field and its radiated noise, we solve the governing equations on approximately 370 million grid points using high-fidelity numerical schemes developed for computational aeroacoustics. Projection of the near-field noise to the far-field is accomplished by coupling the LES data with the Ffowcs Williams–Hawkings method. The main emphasis of these simulations is to compute the jet flow in sufficient detail to accurately capture the physical processes that lead to noise generation. Two separate simulations are performed using turbulent and laminar inflow conditions at the jet nozzle inlet. Simulation results are compared with the corresponding experimental measurements. Results show that nozzle inflow conditions have an influence on the jet flow field and far-field noise.

Noise analysis of the turbojet and turbofan engine tests

2013 ◽  
Vol 228 (13) ◽  
pp. 2414-2423
Author(s):  
Jingjing Huang ◽  
Longxi Zheng
Keyword(s):  
Power Spectrum ◽  
Noise Reduction ◽  
Spectrum Analysis ◽  
Test Bench ◽  
Power Spectrum Analysis ◽  
Noise Power ◽  
Far Field ◽  
Turbofan Engine ◽  
Turbojet Engine ◽  
Field Noise

Aerogine noise leads to environment pollution largely when aerogine is tested. In this paper, the power spectrum analysis method of the aeroengine test noise was discussed, and the noise measurement and analysis experiments of a turbojet engine and a turbofan engine tests were carried out. The noise level, main noise resource, and noise characteristics of the two turbojet and turbofan engines were analyzed. Meanwhile, the indoor noise and far-field noise of the turbojet engine were both measured, the noise spread characteristics were analyzed and the noise reduction performance of the test bench was evaluated. The noise generated by the turbojet engine test had the discrete characteristic of high frequency. The higher frequencies when peak values occurred were the blade passage frequencies and the noises with lower frequencies were the broad band noises, especially the jet noise, and the maximum of the peak values occurred at the basic frequencies or harmonic frequencies of the compressor. Meanwhile, the noises generated by the turbofan engine, focused on the high frequencies and the peak values corresponded to the rotation noise of the fan blades. The experimental results were consistent with the theory basically, which indicated that the aeroengine operating status information could be identified by the noise power spectrum analysis. In addition to the aeroengine noise reduction research, the noise power spectrum analysis could also be used to diagnose the fault of the aeroengine structure and performance. On the other hand, the indoor and far-field noise measurement experimental results implied that the noise was suppressed from 136 dB to 85 dB and could provide the reference to the noise reduction design of the aeroengine test bench.

scholarly journals Predicting Far-Field Noise Generated by a Landing Gear Using Multiple Two-Dimensional Simulations

2019 ◽  
Vol 9 (21) ◽  
pp. 4485
Author(s):  
Sultan Alqash ◽  
Sharvari Dhote ◽  
Kamran Behdinan
Keyword(s):  
Cross Sections ◽  
Near Field ◽  
Computational Cost ◽  
Numerical Data ◽  
Landing Gear ◽  
Design Stage ◽  
Far Field ◽  
Two Dimensional ◽  
Acoustic Analogy ◽  
Field Noise

In this paper, a new approach is proposed to predict the far-field noise of a landing gear (LG) based on near-field flow data obtained from multiple two-dimensional (2D) simulations. The LG consists of many bluff bodies with various shapes and sizes. The analysis begins with dividing the LG structure into multiple 2D cross-sections (C-Ss) representing different configurations. The C-Ss locations are selected based on the number of components, sizes, and geometric complexities. The 2D Computational Fluid Dynamics (CFD) analysis for each C-S is carried out first to obtain the acoustic source data. The Ffowcs Williams and Hawkings acoustic analogy (FW-H) is then used to predict the far-field noise. To compensate for the third dimension, a source correlation length (SCL) is assumed based on a perfectly correlated flow. The overall noise of the LG is calculated as the incoherent sum of the predicted noise from all C-Ss. Flow over a circular cylinder is then studied to examine the effect of the 2D CFD results on the predicted noise. The results are in good agreement with reported experimental and numerical data. However, the Strouhal number (St) is over-predicted. The proposed approach provides a reasonable estimation of the LG far-field noise at a low computational cost. Thus, it has the potential to be used as a quick tool to predict the far-field noise from an LG during the design stage.

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