Near-Field Investigation of Chevron Nozzle Mechanisms

Callender, Bryan; Gutmark, Ephraim; Martens, Steven

doi:10.2514/1.17720

Cited by 77 publications

(38 citation statements)

References 12 publications

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“…In attempts to shed further light on the low-and high-frequency jet noise generation, a series of studies on coaxial jets and different modifications of chevron nozzles at the core jet were conducted by Callender et al [11][12][13]. In their first investigation, chevron nozzles were observed to be more effective at lower acoustic frequencies and aft directivity angles.…”

Section: Circular Coaxial Modified Nozzle Jetsmentioning

confidence: 97%

Dynamics of Jets Issuing from Trailing-Edge Modified Nozzles

New

Tsovolos

Tsioli

2015

Fluid Mechanics and Its Applications

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This chapter will elaborate upon the fundamental flow behaviour associated with vortex-rings and jets issuing from nozzles, where the nozzle trailingedges or lips are physically modified with selected geometries. This technique represents a passive but robust form of manipulating the underlying vortex-ring and jet circulation, such that improvements to their entrainment and mixing characteristics can be achieved. Implementations of simple inclined, hybrid inclined, notched, crown-shaped, chevron and stepped nozzles, as well as some of their implementations in circular and noncircular jets, single-stream or dual-stream coaxial jets, will be discussed as part of the overall understanding. In particular, recently observed influences of trailing-edge modifications upon the axis-switching behaviour of noncircular jets, as well as their relationships with coaxial jet flow parameters such as the velocity-and area-ratios will be presented. On top of key flow physics insights in terms of how the nozzle trailing-edge geometry will confer distortionary effects upon the basic vortex structures, the impact of such nozzles upon jet mixing efficacies will be discussed as well.

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Section: Circular Coaxial Modified Nozzle Jetsmentioning

confidence: 97%

Dynamics of Jets Issuing from Trailing-Edge Modified Nozzles

New

Tsovolos

Tsioli

2015

Fluid Mechanics and Its Applications

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“…Chevroned nozzle lips [1,2], nozzle-exit plasma actuators [3,4], fluidic actuators [5], and many other techniques are currently being explored for this objective. Seemingly without exception, a significant degree of parametric exploration is employed in these efforts.…”

Section: Introductionmentioning

confidence: 99%

Adjoint-based optimization for understanding and suppressing jet noise

Freund

2010

Procedia Engineering

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Advanced simulation tools, particularly large-eddy simulation techniques, are becoming capable of making quality predictions of jet noise for realistic nozzle geometries and at engineering relevant flow conditions. Increasing computer resources will be a key factor in improving these predictions still further. Quality prediction, however, is only a necessary condition for the use of such simulations in design optimization. Predictions do not of themselves lead to quieter designs. They must be interpreted or harnessed in some way that leads to design improvements. As yet, such simulations have not yielded any simplifying principals that offer general design guidance. The turbulence mechanisms leading to jet noise remain poorly described in their complexity. In this light, we have implemented and demonstrated an aeroacoustic adjoint-based optimization technique that automatically calculates gradients that point the direction in which to adjust controls in order to improve designs. This is done with only a single flow solutions and a solution of an adjoint system, which is solved at computational cost comparable to that for the flow. Optimization requires iterations, but having the gradient information provided via the adjoint accelerates convergence in a manner that is insensitive to the number of parameters to be optimized.Keywords: jet noise, optimal control, adjoint-based optimization, computational aeroacoustics BackgroundAircraft jet exhausts remain loud, which continues to motivate efforts to suppress their noise. Chevroned nozzle lips [1, 2], nozzle-exit plasma actuators [3, 4], fluidic actuators [5], and many other techniques are currently being explored for this objective. Seemingly without exception, a significant degree of parametric exploration is employed in these efforts. This is because jet noise, unlike many flow phenomena, has no readily harnessed this-does-that mechanistic description at fixed global flow conditions. We have Lighthill's famous strong power-law sensitivity of radiated power to velocity ("a high power, near the eighth" [6]), but no correspondingly simple guidelines exist for what changes to make at fixed flow condition to suppress noise. The complex interplay between the jet turbulence and radiated sound, added to the underlying complexity of the turbulence itself, is the root cause of this. It is a problem of describing this complexity in a useful way. Acoustic analogy formulations, in which acoustic sources are crafted based upon estimates of turbulence statistics [7,8,9,10], have increased in their robustness to errors in these estimates [11], but such formulations have not yet yielded a flexible general method because they depend upon describing the complexity of the underlying turbulence in an accessible fashion.

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“…In subsonic jets, properly designed chevron nozzles produce lower overall acoustic radiation levels than those of a corresponding round nozzle 6,7,8,9 . Experiments have shown that increasing chevron penetration decreases low frequency noise and often increases high frequency noise (sometimes referred to as high frequency crossover).…”

Section: Introductionmentioning

confidence: 99%

An MDOE Investigation of Chevrons for Supersonic Jet Noise Reduction

Henderson

Bridges

2010

16th AIAA/CEAS Aeroacoustics Conference

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The impact of chevron design on the noise radiated from heated, overexpanded, supersonic jets is presented. The experiments used faceted bi-conic convergent-divergent nozzles with design Mach numbers equal to 1.51 and 1.65. The purpose of the facets was to simulate divergent seals on a military style nozzle. The nozzle throat diameter was equal to 4.5 inches. Modern Design of Experiment (MDOE) techniques were used to investigate the impact of chevron penetration, length, and width on the resulting acoustic radiation. All chevron configurations used 12 chevrons to match the number of facets in the nozzle. Most chevron designs resulted in increased broadband shock noise relative to the baseline nozzle. In the peak jet noise direction, the optimum chevron design reduced peak sound pressure levels by 4 dB relative to the baseline nozzle. The penetration was the parameter having the greatest impact on radiated noise at all observation angles. While increasing chevron penetration decreased acoustic radiation in the peak jet noise direction, broadband shock noise was adversely impacted. Decreasing chevron length increased noise at most observation angles. The impact of chevron width on radiated noise depended on frequency and observation angle.

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Near-Field Investigation of Chevron Nozzle Mechanisms

Cited by 77 publications

References 12 publications

Dynamics of Jets Issuing from Trailing-Edge Modified Nozzles

Dynamics of Jets Issuing from Trailing-Edge Modified Nozzles

Adjoint-based optimization for understanding and suppressing jet noise

An MDOE Investigation of Chevrons for Supersonic Jet Noise Reduction

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