Reduction of Radiation Efficiency in High-Speed Jets

Papamoschou, Dimitri; Xiong, Juntao; Liu, Feng

doi:10.2514/6.2014-2619

Cited by 30 publications

(15 citation statements)

References 27 publications

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“…A significant increase in the convective velocity before the decrease after the potential core length can been seen in the convective velocities reported by Bridges 11 , an effect that would be magnified by a radial location closer to the centerline. Similar trends in convective velocity ratios have been shown by Papamoschou et al 44 Figure 26 (left) shows the 2 nd order auto-spectra at different diameters on the lip line for both cases. The frequency is normalized by the jet velocity and the nozzle diameter, respresenting the Strouhal number (S = / !…”

Section: E Convective Velocitiessupporting

confidence: 81%

Fourth-order Spectral Statistics in the Developing Shear Layers of Hot Supersonic Jets

Ecker¹,

Lowe²,

Ng³

et al. 2014

50th AIAA/ASME/SAE/ASEE Joint Propulsion Conference

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Novel non-intrusive measurements are presented to lend insight into behavior of 4 th order velocity fluctuation spectral statistics and space-time correlations in the developing shear layer of hot supersonic jets. Fourth-order statistics are dominated by the chaotic motion of large-scale coherent structures, which appear largely as the 'skirts' of probity density. Due to the interest in predicting the power spectral spectral density of acoustic density fluctuations, a mean-square quantity, 4 th order statistics hold direct application in acoustic analogies. Despite this, limited data exist for fourth-order spectral correlations of velocity, particularly in hot supersonic jets. A Doppler-based measurement technique with a frequency resolution of 125kHz is employed to obtain time-resolved measurements and used to determine 2 nd and 4 th order space-time correlations, integral timescales, convection velocities and auto-spectra on the lip line of a hot (TTR=1.6 and TTR=2) supersonic perfectly expanded jet at M d =1.65. Comparator data obtained in the same facility using laser Doppler velocimetry is analyzed with respect to 4 th order terms indicating the importance of the 4 th order correlation in the region of immediate interface between the potential core and the shear layer.

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Section: E Convective Velocitiessupporting

confidence: 81%

Fourth-order Spectral Statistics in the Developing Shear Layers of Hot Supersonic Jets

Ecker¹,

Lowe²,

Ng³

et al. 2014

50th AIAA/ASME/SAE/ASEE Joint Propulsion Conference

View full text Add to dashboard Cite

show abstract

“…Following the argument discussed above, this reversal in skewness could indicate that the source events are on the low-speed side of the shear layer. Given that jet noise is directly impacted by the convection velocity (Papamoschou, Xiong & Liu 2014), this result indicates that the COINs reduced jet noise (Murray & Jansen 2012) specifically through a reduction in the eddy convection velocity.…”

Section: Shock Front Source Convection Velocity Resultsmentioning

confidence: 88%

On the convection velocity of source events related to supersonic jet crackle

Murray

Lyons

2016

J. Fluid Mech.

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An image analysis method is developed and applied to shadowgraph images of supersonic jet flow to measure shock front propagation angles at numerous interrogation points distributed throughout the quiescent region outside of the jet shear layer. These shock fronts manifest in acoustic measurements of jet noise as steepened temporal waveforms that have been linked to the perception of crackle. The analysis method uses the Radon transform to quantitatively determine a local shock front propagation angle at each point. The dataset of angles is subsequently used to determine the locations and convection velocities of the sources inside the jet shear layer. The results indicate that the shock-like waves emerge immediately from the jet shear layer and are created by the supersonic convection of coherent structures. The statistical distribution of convection velocities follows an extreme value distribution, indicating that the shock front emitting sources are maxima of the underlying turbulence. A noise reduction method known to reduce the convection velocities in the jet shear layer is applied to the jet to investigate the effect on the shock front emission. The shock front angles change in concert with the reduction in convection velocity giving further evidence that the source of crackle is a flow field event.

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“…The addition of streamwise vorticity reduces the size of the high turbulent kinetic energy region of the jet. As shown by Papamoschou et al 15 , even halving the TKE of the jet should still only reduce the source magnitude by 3 dB. They emphasize that greater noise reduction can be achieved through reduction in radiation efficiency through a decrease in the convective Mach number of the large scale structures.…”

Section: B Experimental Approachmentioning

confidence: 90%

Prediction, Experiments and Optimization of High-Speed Jet Noise Reduction Using Fluidic Inserts

Morris¹,

McLaughlin

Powers

et al. 2014

50th AIAA/ASME/SAE/ASEE Joint Propulsion Conference

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This paper describes several components of a study examining noise reduction in high speed heated jets using fluidic inserts. This noise reduction technology is based on the ideas developed by Seiner and his colleagues at NASA Langley Research Center and the University of Mississippi 1 . That approach was based on the introduction of corrugated seals into the diverging section of a convergent divergent nozzle. These corrugations change the effective area ratio so that the jet operates closer to an on-design condition and reduces broadband shock-associated noise. In addition, the corrugations generate streamwise vorticity that breaks up the large scale structures in the jet and reduces mixing noise. The idea behind fluidic inserts, described by Morris et al. 2 is to generate an equivalent effect with low levels of flow injection in the diverging section of the nozzle. This has the considerable advantage that the fluidic inserts can be controlled actively for maximum noise reduction and performance benefits. The present paper describes recent developments in the optimization of the fluidic insert concept. Flow and noise experiments, including the effect of forward flight are described. Numerical simulations are performed to characterize the flow features generated by the fluidic inserts as well as to develop measures of flow characteristics that can be related to the observed noise changes. These measures can be used to develop a cost function in a design optimization procedure.

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Reduction of Radiation Efficiency in High-Speed Jets

Cited by 30 publications

References 27 publications

Fourth-order Spectral Statistics in the Developing Shear Layers of Hot Supersonic Jets

Fourth-order Spectral Statistics in the Developing Shear Layers of Hot Supersonic Jets

On the convection velocity of source events related to supersonic jet crackle

Prediction, Experiments and Optimization of High-Speed Jet Noise Reduction Using Fluidic Inserts

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