Transverse Jet Research Articles

Direct determination of the gluon density in the proton from jet cross sections in deep-inelastic scattering

A QCD analysis of jet production in deep-inelastic scattering is presented. The studies are based on recent measurements of jet cross sections in the H1 experiment at HERA which are directly sensitive to the gluon density in the proton. The inclusion of H1 data on the inclusive deep-inelastic scattering cross section enables us to perform a consistent, simultaneous determination of the quark and gluon densities in the proton. The gluon density has been determined at fairly large values of 10 −2 < x < 10 −1 at a scale of the order of the transverse jet energies μ f 2 = 200 GeV 2. The result is consistent with indirect determinations from HERA structure function data and extends their range of sensitivity to larger x-values.

Surface Pressure Measurements in Supersonic Transverse Injection Flowfields

Pressure-sensitive paint (PSP) was used to examine the surface pressures in flowfields generated by transverse injection of air through circular and elliptical nozzles into a supersonic freestream. Four jet-to-freestream momentum flux ratios (J) were investigated for each jet. Two different pressure paints (pyrene-based and PtOEP-based) were examined. Results of the paint comparison show that the PtOEP-based paint is significantly more temperature-sensitive than the pyrene-based paint. This results from its longer phosphorescence lifetime as compared to pyrene's short fluorescence lifetime. A comparison of the PSP results with conventional pressure measurements indicates good agreement between the two with no special fitting of the paint data. Results further show that jet operating conditions and injector geometry significantly affect the surface pressure field around a transverse jet. Increases in J dramatically alter the wall pressure field upstream and downstream of the injector. Injector geometry strongly affects the upstream extent of the separation region and the bow shock, and the character of the wake region downstream of the jet. Also, the effective back pressures computed from the PSP data for the elliptical injector cases are significantly higher than for the circular injector cases presenting a possible explanation for recently observed differences in transverse penetration.

NLO QCD predictions for internal jet shapes in DIS at HERA

The transverse momentum flow inside jets is a sensitive measure of internal jet structure. For the current jets in deep inelastic scattering this jet shape measure is determined at order α s 2, i.e. with up to three partons inside a single jet. The scale dependence of jet shapes in various jet algorithms is discussed. Results agree well with recent measurements by the ZEUS Collaboration, without introducing the hadronization parameter R sep.

Penetration and Mixing of Fully Modulated Turbulent Jets in Crossflow

Fully-modulated, incompressible, turbulent transverse jets were studied experimentally over a range of pulsing frequencies, duty-cycles, and at two jet-to-crossflow velocity ratios. The jet flow was completely modulated by operating a solenoid valve resulting in the shut off of jet supply during a portion of the cycle. The planar laserinduced fluorescence technique was used to determine the penetration, dilution, and structural features of the pulsed jets. The molecular mixing rate was quantified through a chemical reaction between the jet and crossflow fluids. Short injection times resulted in creation of vortex ring structures whereas long injection times produced axially elongated turbulent puffs, similar to a segment of the steady jet. The latter case resulted in only modest enhancement of the jet penetration depth and dilution. Pulsed jets dominated by vortex ring had penetration depths significantly greater than a steady jet with the same velocity ratio. Penetration of up to about 5 times the steady jet value at 50 jet diameters downstream of the jet exit was observed with 200 ms pulses. Duty-cycle had a significant effect on the performance of pulsed jets with short injection times. Increasing the duty-cycle for a fixed injection time diminished the jet penetration. The dilution and mixing rates of pulsed jets with short injection time were also increased over the steady jet. The greatest reduction in the mixing rate was approximately 50% for well-separated pulses with short injection times.

Massively separated flows due to transverse sonic jet in laminar hypersonic stream

A numerical simulation of flow interactions due to a transverse sonic jet ejected from a two-dimensional slot into a hypersonic stream is carried out to examine the capability of Navier–Stokes solutions in predicting a massively separated flow upstream of the jet exit. Grid sensitivity has been studied using gradually refined meshes to address the numerical accuracy of the discretised solution of the governing equations. Comparison has been made with published experimental data regarding the separation and reattachment points and the pressure distribution in the separated region. Flow field visualisation provides further insight into the interaction region and reveals a small clockwise vortex immediately ahead of the jet exit, which is found to be responsible for the second peak in the surface pressure distribution.

Measurement of internal jet structure in dijet production in deep-inelastic scattering at HERA

Internal jet structure in dijet production in deep-inelastic scattering is measured with the H1 detector at HERA. Jets with transverse energies E T,Breit > 5 GeV are selected in the Breit frame employing k ⊥ and cone jet algorithms. In the kinematic region of ssquared momentum transfers 10 < Q 2 ⪅ s 120 GeV 2 and Bjorken− x values 2 < 10 −4 ⪅ x Bj ⪅ 8 × 10 −3, jet shapes and subjet multiplicities are measured as a function of a resolution parameter. Distributions of both observables are corrected for detector effects and presented as functions of the transverse jet energy and jet pseudo-rapidity. Dependences of the jet shape and the average number of subjets on the transverse energy and the pseudo-rapidity of the jet are observed. With increasing transverse jet energies and decreasing pseudo-rapidities, i.e. towards the photon hemisphere, the jets are more collimated. QCD models give a fair description of the data.

Measurement of the jet width in γγ collisions and in e+e− annihilation process at TRISTAN

The shape of jets produced in (quasi-) real photon-photon collisions as well as in e + e − annihilation process has been studied with a cone jet finding algorithm, using the data taken with the TOPAZ detector at the TRISTAN e + e − collider at an average center-of-mass energy ( s ee ) of 58 GeV. The results are presented in terms of the jet width as a function of the jet transverse energy ( E T jet) as well as a scaled transverse jet energy, x T (=2 E T jet / s ). The jet width narrows as E jet T increases; however, at the same value of E T jet the jet width in γγ collisions at TRISTAN is significantly narrower than that in γp collisions at HERA. By comparing our results with the data in other reactions, it has been shown that the jet width in γγ, γp, p p ̄ collisions as well as the e + e − annihilation process has an approximate scaling behavior as a function of x T .

Jet cross sections at HERA - current issues

Since the start of HERA operation there has been considerable progress in the understanding of jet production in ep collisions. QCD calculations are now able to accommodate the hadronic structure of the virtual photon. The luminosities delivered by HERA are now sufficient to allow studies of final states in which more than two high transverse energy jets are produced. The transition between jet processes in photoproduction and in deep inelastic scattering has been studied in some detail. These advances are highlighted here.

Flow pattern in the vicinity of an annular system of transverse jets in a supersonic stream

The pattern of the flow in the vicinity of an annular system of jets exiting into a supersonic stream from orifices on a cylindrical surface with a turbulent boundary layer is experimentally investigated Four typical flow regimes are recorded The effect of the jet number and the nozzle-to-outer pressure ratio on the extent of the separation zone and its structure ahead of and behind the jet system is determined

Influence of a counter rotating vortex pair on the stability of a jet in a cross flow: an experimental study by flow visualizations

The loss of stability of a flow resulting from the interaction of a transverse jet and a crossflow has been studied experimentally by means of several nonintrusive optical methods (Laser-Induced Fluorescence, Particle Streak Velocimetry). In particular, flow visualizations have allowed measurement of the characteristic velocity of rotation of a counter-rotating vortex pair, which is the prevailing system of this complex flow. It is shown that the elliptical geometry of the cross sections of these vortex structures can cause the loss of stability of the jet according to the theory of Landman and Saffman (1987). The unstable jet state is characterized by the generation of transverse unsteady rotating structures on the jet boundaries. These transverse eddies are clearly identifiable and their regularity of occurrence is satisfactorily explained by the theory of Landman and Saffman. Therefore, this study shows for the first time that the longitudinal structures must be taken into account in the mechanism of stability arising from the meeting of a jet and a cross stream.

Probing hard color-singlet exchange in [formula omitted] collisions at [formula omitted] = 630 GeV and 1800 GeV

We present results on dijet production via hard color-singlet exchange in proton-antiproton collisions at s =630 GeV and 1800 GeV using the DØ detector. The fraction of dijet events produced via color-singlet exchange is measured as a function of jet transverse energy, separation in pseudorapidity between the two highest transverse energy jets, and proton-antiproton center-of-mass energy. The results are consistent with a color-singlet fraction that increases with an increasing fraction of quark-initiated processes and inconsistent with two-gluon models for the hard color-singlet.

Duty-Cycle Effects on Penetration of Fully Modulated, Turbulent Jets in Crossflow

We study the effects of fully modulated pulsing on the penetration, entrainment, and mixing characteristics of transverse jets in a crossflow. Of particular interest are the specific effects of the pulsing parameters, especially the duty cycle, i.e., the jet-on fraction for each cycle

New experimental observations of vortical motions in transverse jets

Using dye visualization techniques, we have observed vortex structures within the jet region of round transverse jets which, to the best of our knowledge, have not been reported before. These structures confirm the existence of a pair of negative bifurcation lines in the surface flow of the pipe and the conjecture of Abramovich (1963) concerning additional vortical motions within the jet itself.

Exponentially Accelerating Jet in Crossflow

Effects of exponential acceleration on penetration and mixing characteristics of a jet in crosseow have been investigated experimentallyinawatermodel. To imposean exponential acceleration on the eow, both the injection speed and the nozzle width of the jet increased exponentially in the downstream direction of the crosseow. An acceleration parameter ® is dee ned as the ratio of the revolution time of the longitudinal vortex pair to the e-folding time of the acceleration. Theoretically, a signiecant reduction in turbulent entrainment and mixing of the jet with the crosseow is expected as ® nears unity or as the revolution time of the longitudinal vortex pair in the jet becomes comparable to the characteristic time of acceleration. It was found that the diameter of each vortex in the near-eeld jet cross section is reduced more than a factor of three as ® is increased from 0 to 2.5. In the same ® range, the jet eame or reaction length increased up to 50%, revealing a strong effect of the near-e eld forcing on the far-e eld molecular scale mixing. Furthermore, the experiments have shown up to a 50% increase in the penetration of the jet into the crosseow as a result of the acceleration, when compared with a conventional transverse jet. These results demonstrate clearly that, in a free-shear eow, imposing a new timescale by means of an external acceleration ine uences the entrainment and mixing characteristics dramatically, thus providing a new possibility of controlling the eow characteristics.

Some features of body-flow interaction in the presence of transverse jets

A technique for studying the effectiveness of bow thrusters of the "propeller in a tunnel" type is proposed, validated, and checked by testing models in a hydrodynamic tunnel. The interaction of the thruster generated jets with the flow near a ship hull model is studied at low flow velocities. The dependence of the lateral force on the shape of the initial cross section and the relative velocity of the jet outflowing from the thruster tunnel is studied. A strong dependence of the lateral force on the Reynolds number based on the free-stream velocity and the characteristic dimension of the initial jet section is revealed on the range of relative jet velocities investigated. The case of cavitation collision of the thruster jet with the external flow, when a considerable amount of gas is fed into the near wake zone downstream of the jet, is also examined.

Heating enhancement caused by a transverse control jet in hypersonic flow

Experiments are reported in which the heat flux distribution near a single circular, sonic transverse jet on a flat plate exposed to a hypersonic (Mach 6.7) freestream flow was quantitatively measured using thermochromic liquid crystals. The freestream conditions were such that the boundary layer growth on the plate ahead of the jet was laminar. The results indicate that the interaction of the jet with the freestream flow created a complex flowfield with regions of separation and reattachment which caused localised enhancements to the heat flux upstream and to the side of the jet, the magnitudes of which were sensitive to both jet plenum pressure and jet gas composition.

Simultaneous planar velocity measurements and OH imaging in a transverse jet flame

We present simultaneous planar velocity and OH fluorescence measurements at the base of a lifted, nonpremixed, transverse methane jet flame of Reynolds number 6300 and jet-to-crossflow velocity ratio 11.5. Velocity measurements are obtained using particle image velocimetry (PIV), while nonresonant OH fluorescence is imaged via excitation of the A←X (1,0) band near 283 nm. It is shown that at the flame base, the regions in the PIV images where particle density drops due to heat release closely overlap the regions where OH appears. Other preliminary results show that the base of the flame sheet typically resides just above a region where velocity magnitude is locally low, about three times the laminar flame speed, and that the fluid accelerates suddenly through the flame base. Experimental issues such as PIV accuracy and OH imaging in the presence of PIV particles are discussed.

Determination of the shape of the shocks ahead of a transverse jet injected into a supersonic flow

The three-dimensional shape of the shock wave formed ahead of a sonic jet flowing out into a supersonic flow through the surface of a sharp cone is determined. The shape of the wave in the longitudinal and transverse cross-sections of the model is constructed using schlieren photographs taken for various angles of rotation and freestream Mach numbers M=1.75–3.

Measurement of the inclusive di-jet cross section in photoproduction and determination of an effective parton distribution in the photon

The double-differential inclusive di-jet cross section in photoproduction processes is measured with the H1 detector at HERA. The cross section is determined as a function of the average transverse jet energyE T jets for ranges of the fractional energyξ γ jets of the parton from the photon side. An effective leading order parton distribution in the photon is determined at large parton fractional energies for scale between 80 <p T 2 < 1250 GeV2. The measurement is compatible with the logarithmic scale dependence that is predicted by perturbative QCD.

Mixing, structure and scaling of the jet in crossflow

The mixing of the round jet normal to a uniform crossflow is studied for a range of jet-to-crossflow velocity ratios, r, from 5 to 25. Planar laser-induced fluorescence (PLIF) of acetone vapour seeded into the jet is used to acquire quantitative two-dimensional images of the scalar concentration field. Emphasis is placed on r=10 and r=20 and a few select images are acquired up to r=200. The Reynolds number based on the jet exit diameter, d, and the exit velocity varies from 8400 to 41 500. Images are acquired for conditions in which the product rd is held constant, requiring decreasing d for increasing r.Results from this experimental study concern structural events of the vortex interaction region, and mixing and mean centreline concentration decay in the near and far fields. The results cover all three regions of the transverse jet, and suggest that the jet scales with three length scales: d, rd and r2d.Events within the vortex interaction region display d-scaling, including the crossflow boundary layer separation and roll-up. Over the range of velocity ratios studied, the vortex interaction region shows r-dependent variations in the flow field, including the emergence of jet fluid in the wake structures for r&gt;10 and a slower development of the counter-rotating vortex pair (CVP) in higher-r jets.The trajectory and physical dimension of the jet in both the near and far field display rd-scaling. The near field is characterized by a centreline concentration decay along the centreline coordinate s of s−1.3, different from the decay rate (s−1) of the free jet. When normalized by rd, the decay of each velocity-ratio jet branches away from the s−1.3 decay, approaching a decay of s−2/3, a rate predicted by modelling efforts. The branch points represent a transition in the flow field from enhanced mixing to reduced mixing compared to the free jet. When normalized by r2d, the branch points occur at a uniform jet position, s/r2d=0.3, which is viewed to be the division between the near and far fields. Self-similarity is not seen in the near field, but may be present in the far field.The view of the branch points as a place of transition in the flow is supported by the probability density function (p.d.f.) of concentration along the upper edge of the jet. Before the branch points, the p.d.f.s are non-marching in character, and after the branch points, they are tilted in character.Instantaneously, the CVP is asymmetric in shape and concentration. End views reveal extensive motion of the CVP and plan views show this motion can occur in both axisymmetric and sinusoidal motion. Ensemble-averaged images show the jet concentration is asymmetric about the centreline plane.