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Research Papers: Gas Turbines: Aircraft Engine

Crackle Noise in Heated Supersonic Jets

[+] Author and Article Information
Joseph W. Nichols

e-mail: jwn@stanford.edu

Sanjiva K. Lele

Center for Turbulence Research,
Stanford University,
Stanford, CA 94305

Frank E. Ham

Cascade Technologies, Inc.,
Palo Alto, CA 94303

Steve Martens

GE Aviation,
Cincinnati, OH 45215

John T. Spyropoulos

Naval Air Systems Command,
Patuxent River, MD 20670

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the Journal of Engineering for Gas Turbines and Power. Manuscript received June 16, 2012; final manuscript received October 9, 2012; published online April 23, 2013. Editor: Dilip R. Ballal.

J. Eng. Gas Turbines Power 135(5), 051202 (Apr 23, 2013) (7 pages) Paper No: GTP-12-1155; doi: 10.1115/1.4007867 History: Received June 16, 2012; Revised October 09, 2012

Crackle noise from heated supersonic jets is characterized by the presence of strong positive pressure impulses resulting in a strongly skewed far-field pressure signal. These strong positive pressure impulses are associated with N-shaped waveforms involving a shocklike compression and, thus, is very annoying to observers when it occurs. Unlike broadband shock-associated noise which dominates at upstream angles, crackle reaches a maximum at downstream angles associated with the peak jet noise directivity. Recent experiments (Martens et al., 2011, “The Effect of Chevrons on Crackle—Engine and Scale Model Results,” Proceedings of the ASME Turbo Expo, Paper No. GT2011-46417) have shown that the addition of chevrons to the nozzle lip can significantly reduce crackle, especially in full-scale high-power tests. Because of these observations, it was conjectured that crackle is associated with coherent large scale flow structures produced by the baseline nozzle and that the formation of these structures are interrupted by the presence of the chevrons, which leads to noise reduction. In particular, shocklets attached to large eddies are postulated as a possible aerodynamic mechanism for the formation of crackle. In this paper, we test this hypothesis through a high-fidelity large-eddy simulation (LES) of a hot supersonic jet of Mach number 1.56 and a total temperature ratio of 3.65. We use the LES solver CHARLES developed by Cascade Technologies, Inc., to capture the turbulent jet plume on fully-unstructured meshes.

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Figures

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Fig. 1

A military-style nozzle designed by GE with a faceted straight-ramp diffuser used for the crackle simulations

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Fig. 2

(a) An axial cross section showing the mesh resolution in the near-nozzle region. A zone extending 8 jet diameters downstream of the jet exit was adaptively refined. (b) A radial cross section taken through the adaptive refinement region showing the azimuthal resolution and the conformance of the mesh to the twelve-fold symmetry of the nozzle.

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Fig. 3

An instantaneous snapshot of the heated supersonic jet visualized by contours of temperature (interior of the jet, yellow scale online) and contours of pressure (exterior of the jet, blue scale online) on an axial cross section. The nozzle is shown at left.

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Fig. 4

A comparison of the experimental and simulated farfield acoustics at an angle of 140 deg to the jet upstream axis (peak jet noise direction)

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Fig. 5

Pressure signals at inner probe locations (a) 1, (b) 2, and (c) 3. The skewness levels for these three signals are 0.4806, 0.3892, and 0.4396, respectively.

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Fig. 6

(a) Probability distribution function corresponding to the pressure signal at outer probe 2, with skewness 0.4048. (b) Skewness levels versus axial position along the inner (solid curve) and outer (dashed curve) probe arrays. At each station, the skewness was averaged with respect to the azimuthal direction. The error bars indicate the standard deviation of the azimuthal data.

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Fig. 7

(a) Contours of pressure along a portion of the conical FWH surface. (b) The same surface “unwrapped’’ to show the azimuthal dependence of the skewed pressure waves along the entire circumference.

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Fig. 8

Pressure signal with skewness 0.4245 as measured at the outer probe location 2. Four intense crackle events are indicated by the arrows.

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Fig. 9

(a) Pressure signal at times near to crackle event 1. (b)–(d) Time sequence of the flow field evolution leading up to crackle event 1. (e) Pressure signal at times near to crackle event 2. (f)–(h) Time sequence of the flow field evolution leading up to crackle event 2. The jet interior and shears layers are visualized by contours of temperature (grayscale), while pressure contours are shown exterior to the jet (color online). The solid curve (magenta online) represents the sonic line which separates fluid moving supersonically with respect to the ambient from fluid moving subsonically. The circle corresponds to the probe location and the arrows indicate the waves that cause the crackle events.

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Fig. 10

Contours of the shock sensor C on an axial cross section through the heated jet, highlighting shocklets in the near field of the jet. Dashed lines delimit the region of near-nozzle adaptive refinement. Circles indicate locations where the foot of a shocklet is embedded inside the turbulent shear layer.

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