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Some results are presented on the temporal evolution of a large jet in crossflow consisting of the burning plume from an unabated oil well discharge. The volume rendering approach is used whereby several sequential x-y images of t...
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Some results are presented on the temporal evolution of a large jet in crossflow consisting of the burning plume from an unabated oil well discharge. The volume rendering approach is used whereby several sequential x-y images of the jet are stacked in time, t, to produce an object in x-y-t space which can be used to conveniently examine the jet dynamics. Similar to earlier findings for free jets, the burning jet in crossflow is seen to consist of a series of large-scale organized structures which convect downstream leading to a quasiperiodic flame tip burnout. The wake region however is seen to be much less organized. Most surprising is the constant speed of the burning structures as they progress from the jet to crossflow direction. It therefore appears that an underlying organization exists in the jet in crossflow, in spite of its relatively complex, three-dimensional structure. [References: 13]
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This paper studies the trajectories and near field of round jets in crossflow. Incompressible direct numerical simulations are performed at velocity ratios of 1.5 and 5.7 and the effects of jet velocity profile and boundary layer ...
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This paper studies the trajectories and near field of round jets in crossflow. Incompressible direct numerical simulations are performed at velocity ratios of 1.5 and 5.7 and the effects of jet velocity profile and boundary layer thickness on the jet trajectory are examined. The 'rd' scaling used at present (Margason 1993) does not contain any information on these parameters, and trajectories scaled by rd do not collapse. The trajectory is strongly influenced by the near field which depends on both the jet velocity profile and the crossflow boundary layer. A length scale is proposed to describe the near field of the jet. An analytical expression is proposed for this length scale which is a measure of the relative inertia of the jet and the crossflow. Incorporating this length scale significantly improves the scaling of the trajectories.
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A performant identification of the jets originating from b-quarks is one of the key ingredients which allows for the diverse physics program of the ATLAS experiment. Algorithms for the b-jet identification in ATLAS are exploiting ...
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A performant identification of the jets originating from b-quarks is one of the key ingredients which allows for the diverse physics program of the ATLAS experiment. Algorithms for the b-jet identification in ATLAS are exploiting the long lifetime and the high mass of the b-hadrons, as well as the information on the tracks associated with jets. The performance of these algorithms is measured in data to enable reliable usage in the physics analyses. In this article, the performance of the multivariate technique MV1 for b-jet identification, which as its inputs takes information from the other b-jet identification algorithms in ATLAS, is presented. The efficiency of the MV1 algorithm is measured using dileptonic top pair events and is based on a likelihood approach. This approach allows to exploit per-event flavour and momentum correlations between the two jets. Correction factors which take into account differences in the b-jet identification efficiencies in simulation and data are derived as a function of jet transverse momentum and pseudo-rapidity. All the results are derived using the proton-proton collision dataset at centre of mass energy of (1/2)/(s) = 8TeV corresponding to an integrated luminosity of L ≈ 20.3 fb~(-1).
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Water tunnel experiments were conducted to examine the effect of hole exit geometry on the near-field characteristics of crossflow jets. Hole shapes investigated were round, elliptical, square, and rectangular, all having the same...
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Water tunnel experiments were conducted to examine the effect of hole exit geometry on the near-field characteristics of crossflow jets. Hole shapes investigated were round, elliptical, square, and rectangular, all having the same cross-sectional area. Laser-induced fluorescence (LIF) and particle image velocimetry (PIV) were used. The vorticity around the circumference of the jet was tracked to identify its relative contributions to the nascent streamwise vortices, which evolve eventually into kidney vortices downstream. The distinction between sidewall vorticity and that from the leading and trailing edges, though blurred for a round hole, became clear for a square or a rectangular hole. The choice of non-circular holes also made it possible to reveal the unexpected double-decked structures of streamwise vortices and link them to the vorticity generated along the wall of the hole. The lowermost vortex pair of the double-decked structures, located beneath the jet, is what we call a 'steady' vortex pair. This pair is always present and has the same sense of rotation as the kidney vortices. The origin of these lower-deck vortices is the hole sidewall boundary layer: as the jet emanates from the hole, the crossflow forces the sidewall boundary layer to roll up into nascent kidney vortices. Here, hole width sets the lateral separation of these steady sidewall vortices. The vortices comprising the upper deck ride intermittently over the top of the 'steady' lower pair. The sense of rotation of these upper-deck vortices depends on hole geometry and can be the same as, or opposite to, the lower pair. The origin of the upper deck is the hole leading-edge boundary layer. This vorticity, initially aligned transverse to the crossflow direction, is realigned by the entrainment of crossflow momentum and thus induces a streamwise component of vorticity. Depending on hole geometry, this induced streamwise vorticity can be opposite to the lower-deck vortex pair. The opposing pair, called the 'anti-kidney' pair, competes with the nascent kidney-vortices and affects the jet lift-off. The hole trailing-edge boundary layer can likewise be turned toward the streamwise direction. In this case, the turning is caused by the strong reverse flow just downstream of the jet. In the present range of parameters, all hole boundary layer vorticity, regardless of its origin along the hole circumference, is found to influence the kidney vortices downstream. [References: 25]
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The digital particle image velocimetry (DPIV) technique has been used to investigate the flow fields of an elliptic jet in cross flow (EJICF). Two different jet orientations are considered; one with the major axis of the ellipse a...
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The digital particle image velocimetry (DPIV) technique has been used to investigate the flow fields of an elliptic jet in cross flow (EJICF). Two different jet orientations are considered; one with the major axis of the ellipse aligned with the cross flow (henceforth referred to as a low aspect ratio (AR) jet), and the other with the major axis normal to the cross flow (henceforth referred to as a high aspect ratio jet). Results show that the vortex-pairing phenomenon is prevalent in the low aspect ratio jet when the velocity ratio (VR)greater than or equal to3, and is absent in the high aspect ratio jet regardless of the velocity ratio. The presence of vortex pairing leads to a substantial increase in the leading-edge peak vorticity compared to the lee-side vorticity, which suggests that vortex pairing may play an important role in the entrainment of ambient fluid into the jet body, at least in the near-field region. In the absence of vortex pairing, both the leading-edge and the lee-side peak vorticity increase monotonically with velocity ratio regardless of the aspect ratio. Moreover, time-averaged velocity fields for both AR=0.5 and AR=2 jets reveal the existence of an "unstable focus" (UF) downstream of the jet, at least for VRgreater than or equal to2. The strength and the location of this focus is a function of both the velocity ratio and aspect ratio. In addition, time-averaged vorticity fields show a consistently higher peak-averaged vorticity in the low aspect ratio jet than in the high aspect ratio jet. This behavior could be due to a higher curvature of the vortex filament facing the cross flow in the low aspect ratio jet, which through mutual interaction may lead to higher vortex stretching, and therefore higher peak-averaged vorticity.
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Sensitivity to tab disturbance of the mean flow structure of nonswirling jet in crossflow (JICF) and swirling jet in crossflow (SJICF) is investigated. For the swirling jet, the nonzero tangential velocity, nonzero circulation jet...
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Sensitivity to tab disturbance of the mean flow structure of nonswirling jet in crossflow (JICF) and swirling jet in crossflow (SJICF) is investigated. For the swirling jet, the nonzero tangential velocity, nonzero circulation jet configuration is employed. The configuration allows for the development of the skewed mixing layer at each lateral edge of the jet not to be obscured and modulated by the jet cross-stream boundary layer and the associated vorticity of the opposite sign to that of the imposed swirl. In the investigation, a heated jet is used and the temperature distributions in the cross planes downstream of the jets are surveyed upto x/rd=1, where r is the effective velocity ratio and d is the diameter of the jet exit. A single stationary tab is alternately placed at eight different azimuthal positions along the periphery of the jet exit. For both JICF and SJICF, the results show that the mean flow structure is most sensitive to tab disturbance in the region centered on the pressure-windward to the windward position and is less sensitive in the leeward region. Specifically, for JICF the sensitive region covers approximately from lateral to windward; for SJICF, from pressure to suction-windward when moving in the same rotational sense as the swirl. The tab disturbance in these sensitive regions has pronounced and effectively lasting effect on the flow structure; the transformed structure persists downstream to the last measurement station. These results indicate that the generation mechanism of the flow structure in both jets is sensitive to tab disturbance in these regions. They also suggest it to be closely related to the development of the skewed mixing layer along the surrounding crossflow direction and around the jet exit column. (C) 2005 American Institute of Physics.
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Jet dynamics, in particular jet penetration, is an important design parameter affecting the collection efficiency of Venturi scrubbers. A mathematical description of the trajectory, break-up and penetration of liquid jets initiall...
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Jet dynamics, in particular jet penetration, is an important design parameter affecting the collection efficiency of Venturi scrubbers. A mathematical description of the trajectory, break-up and penetration of liquid jets initially transversal to a subsonic gas stream is presented. Experimental data obtained from a laboratory scale Venturi scrubber, operated with liquid injected into the throat through a single orifice, jet velocities between 6.07 and 15.9 m/s, and throat gas velocities between 58.3 and 74.9 m/s, is presented and used to validate the model.
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Experiments were conducted to investigate the impact of circular and noncircular injector nozzle geometries on the penetration, mixing, and structure of a jet injected perpendicular into subsonic cross flow. Circular, triangle, an...
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Experiments were conducted to investigate the impact of circular and noncircular injector nozzle geometries on the penetration, mixing, and structure of a jet injected perpendicular into subsonic cross flow. Circular, triangle, and elongated slot nozzles were studied including varying their orientations relative to the cross flow, to comprise a matrix of five different test cases. The cross-sectional areas of all geometries were equal. The interaction between the jets and the cross flow was strongly dependent on the different geometries and their orientations. Each of the injector geometries resulted in a distinctive region of backflow at the leeward side of the jet. The location and size of this region and the reverse flow magnitude were largely dependent on the aspect ratio and the jet cross section lateral dimension change in the axial direction. A combination of instantaneous and time-averaged particle image velocimetry images taken in the axial and lateral cross sections of the jet near the exit plane revealed several large scale turbulent structures downstream of the jets for two different blowing ratios r=3.2 and 8. Detailed flow field data are presented for the higher blowing ratio due to the better spatial resolution of the large scale structures in the near field. A counter-rotating vortex pair was identified in the near field of the jets resulting in a reverse flow region. These structures had an upright nature similar to the wake vortices with the exception that the former were attached to and constantly fed from jet fluid mixed with the cross flow. The latter was formed by the cross flow, fed from its boundary layer vorticity, and remained separate from the jet. It was attached to the surface of the flat plate at one end and to the trajectory of the bent jet at the other end. Both the shape and orientation of the nozzle geometries had a strong effect on the jet spread and penetration. Compared to the baseline circular nozzle, the slot major (slot nozzle's major axis oriented along the cross stream) exhibited the highest penetration, whereas the slot minor penetrated the least. The triangular jets' characteristics were significantly affected by their orientation relative to the cross flow. Several different scaling techniques were explored in order to compare the present jet trajectories with previously published data. Commonly used length scaling parameters of rd and r(2)d were shown to be inadequate to scale different experimental data. Newly proposed scaling that was based on the velocity profiles of the cross flow boundary layer and the jet, prior to their interaction, yielded better results. (C) 2008 American Institute of Physics.
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The controlled suppression of instabilities, or "relaminarization," in low velocity ratio and Reynolds number elevated jets-in-crossflow (JICFs) is discussed for jet-to-crossflow velocity ratios (R) less than 1.5 and jet Reynolds ...
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The controlled suppression of instabilities, or "relaminarization," in low velocity ratio and Reynolds number elevated jets-in-crossflow (JICFs) is discussed for jet-to-crossflow velocity ratios (R) less than 1.5 and jet Reynolds numbers (Re-d) less than 2000. The principal control method is via a synthetic jet from an annular slit coaxially surrounding the jet flow. Effects of forcing the JICF jet shear layer are studied using photographs obtained by smoke flow visualization, single point hot-wire measurements, and field measurements using a form of image correlation velocimetry on the smoke images. The unforced JICF is unstable in two R regimes separated by a window of stability centered around the velocity ratio R = 1.13. In the lower unstable regime where there is formation of strong jet shear layer instabilities, the synthetic jet can suppress them. A mechanism for the suppression phenomenon is proposed. The synthetic jet reduces the local Reynolds number of a wakelike profile on the upstream side of the JICF between the free stream and jet flow below critical values for growth of an unstable flow structure. The control mechanism has many similarities to base bleed suppression of von Karman vortex shedding in supercritical bluff bodies. A continuous stream from the same annular slit does indeed have a similar suppression effect to synthetic jet forcing. (C) 2008 American Institute of Physics.
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This paper describes an experimental study of reacting jets in a high-temperature (1775 K) vitiated cross-flow at 6 atm. We present an extensive data set based on high speed chemiluminescence imaging and exhaust gas sampling showi...
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This paper describes an experimental study of reacting jets in a high-temperature (1775 K) vitiated cross-flow at 6 atm. We present an extensive data set based on high speed chemiluminescence imaging and exhaust gas sampling showing the characteristics of the time-averaged trajectory, width of the flame, flame standoff (or ignition) location, and NO_x emissions over a momentum flux ratio range of 0.75 ＜ J ＜ 240. Key observations are: (1) Depending upon ignition times, reaction can initiate uniformly around the jet, initiate on the leeward side of the jet and spread around to the windward side farther downstream, or initiate further downstream. (2) The time-averaged trajectory generally follows nonre-acting trajectories, but penetrates further in the far-field than for what would be expected of a nonreact-ing jet. (3)The width of heat release zone increases monotonically with downstream location, J, and flame flapping amplitude, but seems to be dominated by the size of the counter-rotating vortex pair. (4) The measured ignition locations were of the same order of magnitude as values based on calculated ignition time scales and mean jet exit velocities, but with some additional variability. (5) The incremental NO_x emissions were controlled primarily by the global temperature rise associated with burning the jet fuel (for the fixed crossflow conditions studied here), and the NO_x emissions increased roughly linearly with the temperature rise.
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