Structure of a screeching rectangular jet: a stereoscopic particle image velocimetry study

Alkislar, Mehmet; Krothapalli, Anjaneyulu; Lourenco, L.

doi:10.1017/s0022112003005032

Cited by 118 publications

(53 citation statements)

References 22 publications

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“…The instabilities grown during the first pairing appear to be further amplified by the second pairing, due to the larger axial and radial velocity fluctuations induced by the preceding vortex ("1"). In the present case, one observes a tilting up to 30 of the trailing vortex ("2") while moving closer to vortex "1." Temporal fluctuations at a half the frequency (St ¼ 0.16) are observed, which result in further amplification of the pulsating motion.…”

Section: Three-dimensional Regime Of Circular Jetsupporting

confidence: 46%

“…Zaman and Raman 29 placed tabs at the exit of turbulent circular jet reporting a marked loss of azimuthal coherence and the generation of pairs of streamwise vortices, which contribute to the increase of the lateral spreading of the jet along the direction orthogonal to the plane of the tabs. Streamwise structures are also formed in rectangular jets, as shown by the phased-locked stereo PIV measurements by Alkislar et al 30 More recently, El Hassan and Meslem 2 studied the entrainment of circular and daisy-shaped orifice jets at Re ¼ 3600 using time-resolved stereo PIV and snapshot POD analysis. They concluded that the daisy-shaped orifice jet undergoes earlier transition due to the generation of streamwise vortices, with a significant enhancement of the entrainment process.…”

Section: Introductionmentioning

confidence: 91%

“…For a clearer insight in the three-dimensional development, the counter-rotating vortices "SRP" and "STP" (Figure 25) are extracted at t ¼ 0 and, for each of the pair, the streamwise vortex with positive sign of the related vorticity component is illustrated in Figure 28. Vortex filament "ST" extends to 4 jet diameters downstream the nozzle and, at approximately Z ¼ 2.5, it bends inward towards the jet core with an angle of approximately 30 to the axis. The core of the streamwise vortex is stretched in the radial direction, as shown at Z ¼ 1 in Figure 27, with dimension of the major and minor axes of 1/4D and 1/6D based on iso-surface x z ¼ 0.8.…”

Section: -17mentioning

confidence: 99%

“…For both "SR" and "ST," the highest levels of V r activity is observed on the side of the counter rotating vortex, with peaks of 0.2, whereas the tangential velocity V t increases in the downstream direction reaching peaks of 0.2 at Z > 3. Transitional structures are characterized by a recurrent Cshape and are first observed where the streamwise vortices "ST" form approximately 30 with the jet axis (2.5 < Z < 3, Figure 29). Here, a "C" vortex occupies a peripheral location in the shear layer (0.5 < R < 1) that is characterized by Reynolds stress w 0 v 0 r ¼ 0.0025 at both the notch and the apex of the chevron.…”

Section: -19mentioning

confidence: 99%

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Three-dimensional evolution of flow structures in transitional circular and chevron jets

2011

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The three-dimensional behavior of flow transition in circular and 6-chevron jets at Re ¼ 5000 is investigated with experiments conducted on a free water jet by time-resolved tomographic particle image velocimetry. The emphasis is on the unsteady organization of coherent flow structures, which play a role in the generation of acoustic noise. Shedding and pairing of vortices are the most pronounced phenomena observed in the near field of the circular jet. The first and second pairing amplify the axial pulsatile motion in the jet column and lead to the growth of azimuthal waves culminating in the breakup of the vortex ring. Streamwise vortices of axial and radial vorticity are observed in the outer region and move inward and outward under the effect of the vortex rings. In the jet with chevrons, the axisymmetric ring-like coherence of the circular jet is not encountered. Instead, streamwise flow structures of azimuthal vorticity emanate from the chevron apices, and counter-rotating streamwise vortices of axial and radial vorticity develop from the chevron notches. The decay of streamwise vortices is accompanied by the formation of C-shaped structures. The three-dimensional analysis allows quantifying the vortex stretching and tilting activity, which, for the circular jet exit, is related to the azimuthal instabilities and the streamwise vortices connecting the vortex rings. In the chevron jet, stretching and tilting peak during the formation of C-structures. Following Powell's aeroacoustic analogy, the spatial distribution of the source term is mapped, evaluating the temporal derivative of the Lamb vector. The spatio-temporal evolution of such source term is visualized revealing that the events of highest activity are associated with the processes of vortex-ring pairing and vortex-ring disruption for the circular jet, and with the decay of streamwise instabilities and the formation of C-shaped structures for the chevron case.

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Section: Three-dimensional Regime Of Circular Jetsupporting

confidence: 46%

Section: Introductionmentioning

confidence: 91%

Section: -17mentioning

confidence: 99%

Section: -19mentioning

confidence: 99%

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Three-dimensional evolution of flow structures in transitional circular and chevron jets

2011

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“…They are also a favorable choice to achieve thrust vectoring control. In the past several decades, many studies have been carried out to reveal the fundamental characteristics of supersonic jets from various rectangular nozzles [1][2][3][4][5][6]. For instance, in his study regarding the impact of rectangular nozzle aspect ratios on jet noise, Bridges [1] revealed that rectangular nozzles were able to reduce jet noise to a great degree than axisymmetric nozzles.…”

Section: Introductionmentioning

confidence: 99%

An Experimental Study on the Characteristics of Rectangular Supersonic Jet on a Flat Plate

Kwak¹,

Lee²

2016

International Journal of Aeronautical and Space Sciences

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The present study focuses on the characteristics of a supersonic jet flowing from a rectangular nozzle exit on a flat plate. Flow visualization techniques using schlieren and kerosene-lampblack tracing are utilized to investigate shock reflection structures and boundary-layer separations over a flat plate. Wall pressure measurements are also carried out to quantitatively analyze the flow structures. All observations are repeated for multiple jet flow boundary conditions by varying the flap length and nozzle pressure ratio. The experimental results show that the jet flow structures over the flat plate are highly three-dimensional with strong bleeding flows from the plate sides, and that they are sensitive to plate length and nozzle pressure ratio. A multicomponent force measurement device is also utilized to observe the characteristics of the jet flow thrust vectoring over the plate. The maximum thrust deflection angle of the jet is about 8°, demonstrating the applicability of thrust vector control via a flat plate installed at the nozzle exit.

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Coupled fluid and solid evolution in analogue volcanic vents

et al. 2014

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Volcanic eruptions emit rock particulates and gases at high speed and pressure, which change the shape of the surrounding rock. Simplified analytical solutions, field studies, and numerical models suggest that this process plays an important role in the behavior and hazards associated with explosive volcanic eruptions. Here we present results from a newly developed laboratory-scale apparatus designed to study this coupled process. The experiments used compressed air jets expanding into the laboratory through fabricated rock analogue material, which evolves through time during the experiment. The compressed air was injected at approximately 2.5 times atmospheric pressure. We fabricated rock analogues from sand and steel powder samples with a three-dimensional printing process. We studied the fluid development using phase-locked particle image velocimetry, while simultaneously observing the solid development via a video camera. We found that the fluid response was much more rapid than that of the solid, permitting a quasi-steady approximation. In most cases, the solid vent flared out rapidly, increasing its diameter by 20 to 100%. After the initial expansion, the vent and flow field achieved a near-steady condition for a long duration. The new expanded vent shapes permitted lower vent exit pressures and larger jet radii. In one experiment, after an initial vent shape development and establishment of steady flow behavior, rock failure occurred a second time, resulting in a new exit diameter and new steady state. This second failure was not precipitated by changes in the nozzle flow condition, and it radically changed the downstream flow dynamics. This experiment suggests that the brittle nature of volcanic host rock enables sudden vent expansion in the middle of an eruption without requiring a change in the conduit flow.

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Structure of a screeching rectangular jet: a stereoscopic particle image velocimetry study

Cited by 118 publications

References 22 publications

Three-dimensional evolution of flow structures in transitional circular and chevron jets

Three-dimensional evolution of flow structures in transitional circular and chevron jets

An Experimental Study on the Characteristics of Rectangular Supersonic Jet on a Flat Plate

Coupled fluid and solid evolution in analogue volcanic vents

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