On the Structure of Jet Plumes

Fox, J.

doi:10.2514/3.49166

Cited by 29 publications

(4 citation statements)

References 1 publication

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“…In the underexpanded jets, the OASPL reaches a local maximum with increasing nozzle pressure ratio (where the Mach disk starts to emerge). When the Mach disk forms in the underexpanded jets (so-called highly underexpanded [29][30][31][32]), the strength of the centerline pressure fluctuations after the Mach disk gradually decreases with increasing nozzle pressure ratio (jet Mach numbers). Therefore, the OASPL data begin to level off, as shown in Fig.…”

Section: B Correlations Between the Intensity Of Bbsan And Flowfieldmentioning

confidence: 99%

Effects of Jet Temperature on Broadband Shock-Associated Noise

et al. 2015

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This paper describes an experimental study of the effects of jet heating on broadband shock-associated noise. The noise measurements are supplemented with schlieren flow visualizations that show that the appearance of a Mach disk in the shock cell structure is consistent with the saturation of the broadband shock-associated noise levels for both highly under-and overexpanded jets. The effects of jet heating are then described for the design Mach-number-1.5 nozzle operating at four Mach numbers: two overexpanded (M j 1.2 and 1.4), and two underexpanded (M j 1.7 and 1.9). Total temperature ratios in the range of 1.0 to 2.2 are considered in increments of 0.2. These values are chosen to supplement heated air measurements at higher total temperature ratios (between 1.8 to 3.2) and to examine the effects of low levels of heating. It is shown that the peak broadband shock-associated noise rapidly approaches a saturation value in all cases. In the underexpanded cases, the peak broadband shock-associated noise level decreases with increasing total temperature ratio and the reverse is true for the overexpanded cases. Although the changes are very small, a systematic trend can be observed. The spectral shape of fundamental broadband shock-associated noise is found to be very similar for all the cases considered. An empirical prediction model for the fundamental broadband shock-associated noise is proposed. Nomenclature a ∞ = ambient acoustic velocity D = exit diameter of the nozzle D j = fully expanded diameter of the jet plume f = frequency f c = characteristic frequency; U j ∕D j I = intensity of shock noise L = shock cell spacing M a = acoustic Mach number; U j ∕a ∞ M c = convective Mach number; U c ∕a ∞ M d = design Mach number of the nozzle M j = average Mach number of the fully expanded jet R = physical distance of the microphones from the jet exit R e = Reynolds number R prop = propagation distance for the acoustic measurements T o = jet stagnation temperature T ∞ = ambient temperature St = Strouhal number; f∕f c U c

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Section: B Correlations Between the Intensity Of Bbsan And Flowfieldmentioning

confidence: 99%

Effects of Jet Temperature on Broadband Shock-Associated Noise

et al. 2015

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“…Near the jet axis, the flow cannot be turned sharply enough through an oblique shock to maintain axisymmetry and so a normal shock is set up. Outside this so-called 'Mach disc', there remains an oblique shock, leading to an inverted velocity profile (faster on the outside of the jet than on the axis), a slip line between the slower core and faster outer region, and re-acceleration of the core flow downstream of the Mach disc [10], which increases in diameter with increasing levels of underexpansion [11]. The flow structure of a highly underexpanded jet can lead to some apparently anomalous results when a series of radial pitot traverses is conducted at various streamwise positions.…”

Section: Highly Underexpanded Jetsmentioning

confidence: 99%

A review of jet mixing enhancement for aircraft propulsion applications

Knowles

Saddington

2006

Proceedings of the Institution of Mechanical Engineers, Part G:

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This article reviews techniques applicable to enhancing the mixing of jets, with particular emphasis on infrared (IR) signature reduction of high-speed jets. Following a brief introduction to the IR signature of jet plumes and the fundamentals of jet mixing, this paper discusses rapid mixing technologies under the categories of: geometric modifications (to the nozzle); high shear stress mixing; normal stress mixing; self-acoustic excitation; external acoustic excitation; mechanically oscillated; self-oscillated. It is shown that mixing enhancements of the order of 100 per cent are possible with some techniques and that by combining techniques this can be increased by at least as much again. Simple geometric calculations are presented which demonstrate that with rectangular nozzles such high levels of mixing enhancement may be necessary in order to reduce IR signature. Some apparent rapid mixing technologies, however, have been shown to increase jet spreading without increasing entrainment, whereas other techniques can reduce entrainment as easily as they can increase it.

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“…Under-expanded jets are complex high-speed flows, which are also formed in many other engineering applications and devices such as exhaust aircraft plumes (rockets and missiles), supersonic combustion chambers, actuators, etc. [18][19][20]. This type of jet can also be observed in geophysical systems (volcanic eruption) and in the accidental release of hazardous gases (such as hydrogen) from tiny cracks in high-pressure pipelines and reservoirs [21][22][23].…”

Section: Introductionmentioning

confidence: 99%

Under-Expanded Jets in Advanced Propulsion Systems—A Review of Latest Theoretical and Experimental Research Activities

Duronio,

Villante,

De Vita

2023

Energies

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The current ongoing rise in environmental pollution is leading research efforts toward the adoption of propulsion systems powered by gaseous fuels like hydrogen, methane, e-fuels, etc. Although gaseous fuels have been used in several types of propulsion systems, there are still many aspects that can be improved and require further study. For this reason, we considered it important to provide a review of the latest research topics, with a particular focus on the injection process. In advanced engine systems, fuel supply is achieved via enhanced direct injection into the combustion chamber. The latter involves the presence of under-expanded jets. Under-expanded jets are a particular kind of compressible flow. For this reason, the review initially provides a brief physical explanation of them. Next, experimental and numerical CFD investigation techniques are discussed. The last section of this manuscript presents an analysis of the jet’s structure. The injection parameters commonly used are examined; next, the characteristics of the near-nozzle field are reviewed and finally, the far-field turbulent mixing, which strongly affects the air–fuel mixture formation process, is discussed.

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On the Structure of Jet Plumes

Cited by 29 publications

References 1 publication

Effects of Jet Temperature on Broadband Shock-Associated Noise

Effects of Jet Temperature on Broadband Shock-Associated Noise

A review of jet mixing enhancement for aircraft propulsion applications

Under-Expanded Jets in Advanced Propulsion Systems—A Review of Latest Theoretical and Experimental Research Activities

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