Penetration and Mixing of Fully Modulated Turbulent Jets in Crossflow

Johari, Hamid; Pacheco-Tougas, M.; Hermanson, James C.

doi:10.2514/2.7532

Cited by 139 publications

(36 citation statements)

References 22 publications

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“…Taken together, these observations exclude a simple model of the jet based on a train of coaxial vortex rings. On the other hand, they may help explain the decrease in jet penetration depth observed by Johari et al 6 for fully pulsed jets in crossflow as the duty cycle (equivalently, Sr L ) increased because more coherent vortical structures would tend to penetrate the crossflow more directly and mix less effectively.…”

Section: Discussionmentioning

confidence: 82%

“…4,5 Pulsed jets with a period of no-flow between pulses are sometimes called fully pulsed 4 or fully modulated jets. 6 Most of the work on pulsed jets has focused on utilizing jet unsteadiness to enhance mixing or on understanding the overall evolution of the jet flowfield to model and/or control jet turbulence. Some work, for example, that of Wilson and Paxson 7 and Sarohia et al, 8 has also considered pulsed jets in conjunction with ejectors to enhance thrust augmentation of ejector configurations.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Thrust Augmentation and Vortex Ring Evolution in a Fully-Pulsed Jet

Krueger

Gharib

2005

AIAA Journal

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The time-averaged thrust of an incompressible fully pulsed jet containing a period of no flow between pulses is studied experimentally as a function of pulsing duty cycle Sr L and the ratio of the ejected slug length (per pulse) to the jet diameter L/D. The parameter ranges investigated were 2 < -L/D < -6 and 0.1 < -Sr L < -0.98. Significant thrust augmentation by pulsing was observed over the entire parameter range tested, both in terms of thrust compared to an equivalent steady jet with identical mass flux, denoted F SJ > 1, and in terms of thrust compared to an equivalent intermittent jet where vortex ring formation by pulsation was ignored, denoted F IJ > 1. F SJ as high as 1.90 (90% thrust augmentation) was observed for the smaller L/D as Sr L approached 1.0 (with larger F SJ at lower Sr L ). The F IJ results, which directly measured overpressure at the nozzle exit plane developed during vortex ring formation as the mechanism responsible for thrust augmentation, showed reduced augmentation at large L/D and Sr L . The L/D dependence of F IJ parallels single-pulse (Sr L = 0) results previously studied by the authors. The Sr L dependence of F IJ was linked to the interaction of forming vortex rings with vorticity from preceding pulses using digital particle image velocimetry (DPIV) measurements of the vorticity field. DPIV also revealed that the vortex rings tended to wander off axis and disintegrate as Sr L became sufficiently large.

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Section: Discussionmentioning

confidence: 82%

Section: Introductionmentioning

confidence: 99%

Thrust Augmentation and Vortex Ring Evolution in a Fully-Pulsed Jet

Krueger

Gharib

2005

AIAA Journal

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“…The vast majority of transverse jet studies have focused on the steady jet, yet active control of the mixing processes associated with the jet in crossflow often requires temporal excitation of the jet flow field. Recent experiments on pulsed transverse jets (Vermeulen, Grabinski & Ramesh 1992;Kelso et al 1996;Johari, Pacheco-Tougas & Hermanson 1999;Schuller et al 1999;Eroglu & Breidenthal 2001) suggest that temporally varying the jet velocity U j allows jet penetration and spread to be enhanced at specific conditions of excitation, probably due to control of the temporal generation of jet vorticity. For example, in the study of fully modulated liquid jets in crossflow by Johari et al (1999), the maximum jet penetration occurs at a forcing frequency, f, which corresponds to a jet Strouhal number St j ≡ fD/Ū j = 0.004, where D is the inner diameter of the jet orifice andŪ j is the mean jet velocity.…”

Section: Introductionmentioning

confidence: 99%

The actively controlled jet in crossflow

et al. 2002

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This study quantifies the dynamics of actuation for the temporally forced, round gas jet injected transversely into a crossflow, and incorporates these dynamics in developing a methodology for open loop jet control. A linear model for the dynamics of the forced jet actuation is used to develop a dynamic compensator for the actuator. When the compensator is applied, it allows the jet to be forced in a manner which results in a more precisely prescribed, temporally varying exit velocity, the RMS amplitude of perturbation of which can be made independent of the forcing frequency. Use of the compensator allows straightforward comparisons among different conditions for jet excitation. Clear identification can be made of specific excitation frequencies and characteristic temporal pulse widths which optimize transverse jet penetration and spread through the formation of distinct, deeply penetrating vortex structures.

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“…Other studies of turbulent mixing in transverse jets with additional complexity have been reported, e.g. for jets with swirl (Niederhaus et al 1997), sonic jets injected into a supersonic crossflow (VanLerberghe et al 2000), and fully modulated jets (Johari, Pacheco-Tougas & Hermanson 1999).…”

Section: Introductionmentioning

confidence: 99%

Reynolds-number effects and anisotropy in transverse-jet mixing

Shan

Dimotakis

2006

J. Fluid Mech.

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Experiments are described which measured concentration fields in liquid-phase strong transverse jets over the Reynolds-number range 1.0 × 10 3 6 Re j 6 20 × 10 3 . Laserinduced-fluorescence measurements were made of the jet-fluid-concentration fields at a jet-to-freestream velocity ratio of V r = 10. The concentration-field data for far-field (x/d j = 50) slices of the jet show that turbulent mixing in the transverse jet is Reynoldsnumber dependent over the range investigated, with a scalar-field PDF that evolves with Reynolds number. A growing peak in the PDF, indicating enhanced spatial homogenization of the jet-fluid concentration field, is found with increasing Reynolds number. Comparisons between transverse jets and jets discharging into quiescent reservoirs show that the transverse jet is an efficient mixer in that it entrains more fluid than the ordinary jet, yet is able to effectively mix and homogenize the additional entrained fluid. Analysis of the structure of the scalar field using distributions of scalar increments shows evidence for well-mixed plateaux separated by sharp cliffs in the jet-fluid concentration field, as previously shown in other flows. Furthermore, the scalar field is found to be anisotropic, even at small length scales. Evidence for local anisotropy is seen in the scalar power spectra, scalar microscales, and PDFs of scalar increments in different directions. The scalar-field anisotropy is shown to be correlated to the vortex-induced large-scale strain field of the transverse jet. These experiments add to the existing evidence that the large and small scales of high-Schmidt-number turbulent mixing flows can be linked, with attendant consequences for the universality of small scales of the scalar field for Reynolds numbers up to at least Re = 20 × 10 4 .

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Penetration and Mixing of Fully Modulated Turbulent Jets in Crossflow

Cited by 139 publications

References 22 publications

Thrust Augmentation and Vortex Ring Evolution in a Fully-Pulsed Jet

Thrust Augmentation and Vortex Ring Evolution in a Fully-Pulsed Jet

The actively controlled jet in crossflow

Reynolds-number effects and anisotropy in transverse-jet mixing

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