Further experimental results for three- dimensional free jets.

Sforza, Pasquale M.; Trentacoste, N.

doi:10.2514/3.4096

Cited by 189 publications

(36 citation statements)

References 3 publications

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“…This region bears the influence of the initial geometry of nozzle. Further downstream is an axisymmetric (round cross section) decay region, which contains axisymmetric flow that is independent of nozzle configuration131415161718. Note the phenomenon that we identify, question and explain in this paper: the jet cross section evolves from nozzle-shaped to round, not the other way.…”

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confidence: 73%

Evolution: Why all plumes and jets evolve to round cross sections

Bejan

Ziaei

Lorente

2014

Sci Rep

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Turbulent curtains of smoke rise initially as flat plumes and, above a certain height, they become round plumes. The same evolution of cross-sectional shape is exhibited by jets issuing from flat nozzles. Here we predict based on principle that all such flows should evolve their cross-sectional shapes from flat to round (and not the other way) at a critical distance downstream, which is predictable. The principle is that the prevailing flow architecture provides greater access to the flow of momentum from the moving core (plume, jet) to the still surroundings. For turbulent plumes and jets, the transition distance scales with the long dimensions (L) of the two-dimensional (flat) heat sources and nozzles that drive them. For laminar jets, the transition distance scales with L Re, where Re is the Reynolds number based on nozzle velocity and the smaller dimension of the nozzle cross section. These predictions are confirmed by full numerical experiments of the three-dimensional flow fields of turbulent and laminar jets covering the Re range 10–104.

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confidence: 73%

Evolution: Why all plumes and jets evolve to round cross sections

Bejan

Ziaei

Lorente

2014

Sci Rep

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“…Finally, main concluding remarks will be drawn in the last chapter and some considerations and recommendations for future work will be proposed. (Sforza et al 1966, Trentacoste & Sforza 1967. Later studies of jets emerging from noncircular nozzles with corners showed that the introduction of sharp corners in the nozzle can increase significantly the fine-scale turbulence at the corners relative to the flat segments of the nozzle (Schadow et al 1988, Toyoda & Hussain 1989 and enhance mass entrainment (Vandsburger & Ding 1995).…”

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confidence: 99%

On starting square jets and forced plumes

Ai¹

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The present research focuses on the studies of the transitional stage of jets and plumes. It can be generally divided into two parts, namely, starting jets and starting forced plumes. The first part attempts to improve the understanding of the vortex dynamics in starting jets and to examine the differences between that of the circular jets and square jets. Based on the qualitative (via PLIF) and quantitative results obtained (via PIV), it was found that streamwise vortices generated at the corners of the square nozzle interacted with the primary vortices. The interactions had altered the downstream flow characteristics tremendously. Vortex pinch-off, leapfrogging, coalescence and axis-switching were observed in starting square jets and the mechanisms were analyzed. For starting forced plume, Boussinesq and non-Boussinesq cases had been investigated analytically and experimentally. An analytical model for the starting forced plume covering the entire range of jet-like, transitional and plume-like had been developed based on the understanding Wang & Law (2002) for forced plumes. The velocity ratio between the head vortex and the trailing buoyant jet was derived to vary from the jet-like to plume-like phases. The transitional changes for this ratio had also been quantified. Experimental results verified the analytical model. The quantative PIV results showed disorder behaviors in the near-field region for the non-Boussinesq cases (15% ∆ >). Virtual origin correction approach was utilized to compensate the non-Boussinesq effects.

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“…In addition, the spreading rate is usually higher along the minor axis. 7 Another important feature observed in non-axisymmetric jets is axis switching phenomena: as the jet spreads, its cross-section evolves with the same shape as that at the jet exit but with its axis rotated at a certain angle depending on the particular jet geometry. 6,8,9 Several of these unique features of non-axisymmetric jets can be analyzed by studying the formation, interaction and breakdown of coherent structures in the core.…”

Section: Introductionmentioning

confidence: 99%

Effect of Asymmetric Nozzle Configuration on Jet Flow Characteristics

Sengupta

Agostini

Gaitonde

2016

46th AIAA Fluid Dynamics Conference

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A Large Eddy Simulation based investigation is performed on a circular to rectangular 0.226 Mach jet to understand the effect of the non-axisymmetric geometry on the jet flow dynamics. The nozzle has a circular cross-section at the inlet and a 2:1 aspect ratio rectangular cross-section at the exit. The Reynolds number of the flow is 73,242 and the nozzle has an equivalent diameter of 0.054 meters. Comparison with experiments, indicate a good match of the normalized mean and rms velocities along the jet centerline. Q-criterion isolevels confirm the existence of large hairpin like vortices, which initially are dominant along the major axis but further downstream appear along the minor axis as well. The Joint Probability Density Function (JPDF) analysis is used to study flow along major and minor axis of the rectangular jet as well as an equivalent circular nozzle. Variations in entrainment and ejection-like patterns along the minor and major axes of the rectangular jet are quantified. Results with an equivalent circular nozzle are compared which indicate enhanced ejection and entrainment like motions for the rectangular nozzle compared to the equivalent circular nozzle.

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Further experimental results for three- dimensional free jets.

Cited by 189 publications

References 3 publications

Evolution: Why all plumes and jets evolve to round cross sections

Evolution: Why all plumes and jets evolve to round cross sections

On starting square jets and forced plumes

Effect of Asymmetric Nozzle Configuration on Jet Flow Characteristics

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