Jet Profile Research Articles

Jet Dynamics Associated with Drop Impact on Micropillared Substrate

The jetting phenomenon associated with droplet impact upon a hydrophilic micropillared substrate was analyzed in detail using a high-speed camera. Viscosities of the fluids were varied using differing concentrations of glycerol in deionized water. This paper aims to connect similarities between this form of capillary jetting and another well-known jetting phenomenon from the bubble bursting. Both experience a cavity collapse when opposing fluid fronts collide which causes a singularity at the liquid surface, thus leading to the occurrence of jetting. Following processes used to define scaling laws for bubble bursting, a similar approach was taken to derive scaling laws for the dimensionless jet height, jet radius, base height, and radius of the jet base with respect to dimensionless time for the jetting phenomenon associated with the droplet impact. The development of a top droplet before the breakup of the jet also allows the examination of a scaling law for the necking diameter. We find that with the proper scaling factors, the evolution of the jet profile can collapse into a master profile for different fluids and impact velocities. The time dependence of the necking diameter before the jet breakup follows the power law with an exponent of ~2/3. Contrastingly, for other jet parameters such as the radius and height, the power law relationship with time dependence was not found to have a clear pattern that emerged from these studies.

Seasonal velocity variations over the entire Kuroshio path part II: dynamical interpretation for the current speed variation

The response of a jet to sudden winds was examined using a simple numerical regional model and an analytical model to investigate the mechanism underlying the local wind dynamics of seasonal velocity variations in the upper layer of the Kuroshio. The numerical model was used to simulate the distinct seasonal features in summer and autumn in the East China Sea and successfully reproduced the seasonal features in the velocity field under different sudden wind conditions. The current speed increased and decreased under summer and autumn wind conditions, respectively; and the current axis shifted to the offshore and inshore sides under summer and autumn wind conditions, respectively. We focused on the current speed variation and hypothesized that the current speed variation is forced by the thermocline variation due to nonlinear Ekman pumping. This hypothesis was examined using a rigid-lid reduced-gravity analytical model with Ekman layer dynamics. The analytical model results showed that the asymmetry of the jet profile has a marked effect on the current speed variation. With a higher wavenumber on the west side of a northward jet, the current speed increased and decreased under summer and autumn wind conditions, respectively. These findings can be used to explain the seasonal velocity variations in the upper layer in the East China Sea and over the entire Kuroshio path.

Direct Numerical Simulation of Turbulent Heat Transfer at Low Prandtl Numbers in Planar Impinging Jets

DNS simulations of planar impinging jets are performed to provide reference data to validate RANS models for low-Prandtl turbulent heat transfer. In that configuration, a hot plane jet is blown from a slot at the top wall of a channel and impinges on the cooler bottom wall. The present DNS simulations are carried out at Re=4000 and 5700, based on the jet width and velocity, and for Pr down to 0.01. Two cases are investigated: the case of a laminar uniform jet profile and the case of a fully turbulent inlet profile coming from an auxiliary channel flow simulation running in parallel. The DNS results show how the heat transfer in this configuration evolves from the turbulence-dominated case at Pr=1 to the molecular diffusion-dominate case at Pr=0.01. The temperature field at Pr=0.01 is much smoother than at higher Prandtl number because the much larger heat diffusivity quickly diffuses the temperature fluctuations. The comparison between the laminar and the fully-developed turbulent inflows also show different heat transfer characteristics in the vicinity of the stagnation point, depending on the presence of velocity fluctuations in the bottom-wall boundary layers.

Pitot probe response for pulsed supersonic gas flow characterization in beam profile monitor.

For beam profile measurement of high-intensity proton beams in the low-energy high-intensity proton accelerator at Bhabha Atomic Research Centre, a recent noninvasive technique based on gas sheets will be explored. The gas sheet for this instrument needs to be characterized for calibration and fine tuning of the sheet properties to provide better profile measurements. Pulsed sheet generators for similar applications have been characterized using movable vacuum chambers with a small slit and a gauge mounted inside. Pitot probes are more compact instruments and have been used to measure gas jet profiles in molecular beam applications where the jet was not pulsed. The performance of Pitot probes in the measurement of pulsed supersonic gas flow in vacuum was, therefore, investigated in this work. A test system was developed to generate a pulsed supersonic gas jet in vacuum, and a Pitot probe was inserted into the flow at various axial locations with respect to the nozzle. Measurements taken along the nozzle axis using this probe, as well as the axial Mach number and impact pressure computed using computational fluid dynamics and direct simulation Monte Carlo algorithms, were compared with fitting formulas. Schlieren images of the jet with and without the Pitot tube were also taken under different vacuum conditions.

Decay of stationary capillary waves on impinging liquid jets

This study is concerned with the capillary-wave field generated at the base of a liquid jet impinging on a liquid reservoir. Capillary waves on laminar liquid jets are investigated in terms of the spatial damping coefficient. We find an exponential decrease of the wave crests, with the decay rate given by theory. We show that a small increase in viscosity leads to rapid suppression of the wave-like behavior. This study also emphasizes the effect of viscoelasticity, which decreases the damping coefficient. A simple dependence on the combined Weber–Deborah number is proposed for the dimensionless damping coefficient. At the impact zone, similarities are found for the decay of the free surface compared to the classic model of a meniscus climbing on a cylindrical fiber, the radial jet profile taking the shape of a catenary curve. Theoretical predictions are found to be in good qualitative agreement with the experimental data.

Evaluation and Optimization of Geometric Deviations in Abrasive Water Jet Profile Cutting of Inconel 617

Abstract Inconel 617, an extremely hard-to-machine nickel-based superalloy, is used for high-temperature applications in ultra-supercritical power plants for components like headers, pipes, and turbine blades. Conventional machining of superalloys has been widely explored and is plagued by productivity and quality issues. Nontraditional processing is seen as an effective alternative, and abrasive water jet is a capable method. Optimization involving weighted principal components and a genetic algorithm is detailed for the abrasive water jet process. Water pressure, abrasive mass flow, stand-off distance, and traverse speed are the predominant factors affecting the process. Performance characteristics are material removal rate and surface roughness. Geometric deviations like circularity, cylindricity, perpendicularity, and parallelism, which are mostly neglected, have been investigated. Analysis of variance has been reported indicating the predominant factors. Geometric deviations are consolidated into a geometric index using weighted principal components. Simultaneous multiresponse optimization is performed using multi-objective genetic algorithm and a Pareto-front. From the Pareto-front a geometric index of 0.02036 was obtained at water pressure of 266.03 MPa, standoff distance of 4.27 mm, abrasive mass flow of 0.41 kg/min, and traverse speed of 58.98 mm/min. Material removal rate of 495.42 mm3/min was obtained at water pressure of 266.29 MPa, standoff distance of 4.48 mm, abrasive mass flow of 0.40 kg/min, and traverse speed of 63.11 mm/min. Surface roughness of 6.6364 μm was obtained at water pressure of 266.43 MPa, standoff distance of 4.43 mm, abrasive mass flow of 0.42 kg/min, and traverse speed of 57.48 mm/min. The sets obtained are a compromise between the different output values and provide an optimal parameter setting for the abrasive water jet process. This tool is essential when a large database is available, and it could be used to obtain a set of solutions based on the different machining characteristics that are required from the process.

Attached and Attaching Three-Dimensional Jets From Circular Nozzles: Analytical Model

Abstract Here we consider velocity profiles of three dimensional attaching and attached jets emerging from circular nozzles. Like their well-studied two-dimensional counterparts, these wall jets lose momentum due to interactions with nearby surfaces. Unlike their two-dimensional counterparts, simple and quantitative expressions for the velocity profiles of three-dimensional wall jets remain elusive. Here we present a quantitative analytical model of the three-dimensional velocity profiles of attached jets inclusive of a local skin coefficient of friction. We compare these expressions to experimental velocity profiles at moderate and high nozzle Reynolds numbers to find reasonable quantitative agreement. This work has implications for a variety of industries including nuclear waste processing, where jet flows in mixing vessels suspend solids and gases trapped in radioactive waste tanks.

On the role of thermo-transport properties in the convective/absolute transition of heated round jets

The effect of thermodynamic and transport properties on the convective-to-absolute transition in heated round jets is investigated with the spatio-temporal linear stability theory, by considering three sets of properties with increasing complexity. Present models include (i) a constant property model often used in the literature, (ii) a simplified model with variable properties, and (iii) a more accurate equilibrium air mixture model, accounting for dissociation reactions in the flow. A family of arbitrary single-stream and dual-stream jet profiles, representative of typical configurations studied in the literature, is investigated and adapted to each model. Our results show that considering a variable viscosity and thermal conductivity has a destabilizing effect on absolute instabilities in the viscous regime. Furthermore, this destabilization is stronger for the outer mode in dual-stream jets than for the inner mode or the jet-column mode in single-stream jets. With sufficient heating (S < 0.3), results obtained with the equilibrium model strongly depart from those of calorically perfect gas models and display absolute domains deformed by the chemical activity. For absolute instabilities triggered by the baroclinic torque such as jet-column and inner modes, the convective-to-absolute transition is shifted toward thinner and hotter configurations, while the opposite is observed for the outer mode. Finally, we observe a dependence of the equilibrium model stability properties on the static pressure.

Measurement of inclusive charged-particle jet production in Au + Au collisions at sNN=200 GeV

The STAR Collaboration at the Relativistic Heavy Ion Collider reports the first measurement of inclusive jet production in peripheral and central Au+Au collisions at $\sqrt{s_{NN}}$=200 GeV. Jets are reconstructed with the anti-k$_{T}$ algorithm using charged tracks with pseudorapidity $|\eta|<1.0$ and transverse momentum $0.2<p_{T,jet}^{ch}<30$ GeV/$c$, with jet resolution parameter $R$=0.2, 0.3, and 0.4. The large background yield uncorrelated with the jet signal is observed to be dominated by statistical phase space, consistent with a previous coincidence measurement. This background is suppressed by requiring a high-transverse-momentum (high-$p_T$) leading hadron in accepted jet candidates. The bias imposed by this requirement is assessed, and the $p_T$ region in which the bias is small is identified. Inclusive charged-particle jet distributions are reported in peripheral and central Au+Au collisions for $5<p_{T,jet}^{ch}<25$ GeV/$c$ and $5<p_{T,jet}^{ch}<30$ GeV/$c$, respectively. The charged-particle jet inclusive yield is suppressed for central Au+Au collisions, compared to both the peripheral Au+Au yield from this measurement and to the $pp$ yield calculated using the PYTHIA event generator. The magnitude of the suppression is consistent with that of inclusive hadron production at high $p_T$, and that of semi-inclusive recoil jet yield when expressed in terms of energy loss due to medium-induced energy transport. Comparison of inclusive charged-particle jet yields for different values of $R$ exhibits no significant evidence for medium-induced broadening of the transverse jet profile for $R<0.4$ in central Au+Au collisions. The measured distributions are consistent with theoretical model calculations that incorporate jet quenching.

Coating Flow Near Channel Exit. A Theoretical Perspective

The planar flow of a steady moving-wall free-surface jet is examined theoretically for moderate inertia and surface tension. The method of matched asymptotic expansion and singular perturbation is used to explore the rich dynamics near the stress singularity. A thin-film approach is also proposed to capture the flow further downstream where the flow becomes of the boundary-layer type. We exploit the similarity character of the flow to circumvent the presence of the singularity. The study is of close relevance to slot and blade coating. The jet is found to always contract near the channel exit, but presents a mild expansion further downstream for a thick coating film. We predict that separation occurs upstream of the exit for slot coating, essentially for any coating thickness near the moving substrate, and for a thin film near the die. For capillary number of order one, the jet profile is not affected by surface tension but the normal stress along the free surface exhibits a maximum that strengthens with surface tension. In contrast to existing numerical findings, we predict the existence of upstream influence as indicated by the nonlinear pressure dependence on upstream distance and the pressure undershoot (overshoot) in blade (slot) coating at the exit.

Relativistic AGN jets – III. Synthesis of synchrotron emission from double-double radio galaxies

ABSTRACTThe class of double-double radio galaxies (DDRGs) relates to episodic jet outbursts. How various regions and components add to the total intensity in radio images is less well known. In this paper, we synthesize synchrotron images for DDRGs based on special relativistic hydrodynamic simulations, making advanced approximations for the magnetic fields. We study the synchrotron images for three different radial jet profiles; ordered, entangled, or mixed magnetic fields; spectral ageing from synchrotron cooling; the contribution from different jet components; the viewing angle and Doppler (de-)boosting; and the various epochs of the evolution of the DDRG. To link our results to observational data, we adopt to J1835+6204 as a reference source. In all cases, the synthesized synchrotron images show two clear pairs of hotspots, in the inner and outer lobes. The best resemblance is obtained for the piecewise isochoric jet model, for a viewing angle of approximately ϑ ∼ −71°, i.e. inclined with the lower jet towards the observer, with predominantly entangled (≳70 per cent of the magnetic pressure) in turbulent, rather than ordered fields. The effects of spectral ageing become significant when the ratio of observation frequencies and cut-off frequency νobs/ν∞, 0 ≳ 10−3, corresponding to ∼3 × 102 MHz. For viewing angles ϑ ≲ |−30°|, a DDRG morphology can no longer be recognized. The second jets must be injected within ≲ 4 per cent of the lifetime of the first jets for a DDRG structure to emerge, which is relevant for active galactic nuclei feedback constraints.

The Range of Jupiter's Flow Structures That Fit the Juno Asymmetric Gravity Measurements

AbstractThe asymmetric gravity field measured by the Juno spacecraft has allowed the estimation of the depth of Jupiter's zonal jets, showing that the winds extend approximately 3,000 km beneath the cloud level. This estimate was based on an analysis using a combination of all measured odd gravity harmonics, J3, J5, J7, and J9, but the wind profile's dependence on each of them separately has yet to be investigated. Furthermore, these calculations assumed the meridional profile of the cloud‐level wind extends to depth. However, it is possible that the interior jet profile varies somewhat from that of the cloud level. Here we analyze in detail the possible meridional and vertical structure of Jupiter's deep jet streams that can match the gravity measurements. We find that each odd gravity harmonic constrains the flow at a different depth, with J3 the most dominant at depths below 3,000 km, J5 the most restrictive overall, whereas J9 does not add any constraint on the flow if the other odd harmonics are considered. Interior flow profiles constructed from perturbations to the cloud‐level winds allow a more extensive range of vertical wind profiles, yet when the meridional profiles differ substantially from the cloud level, the ability to match the gravity data significantly diminishes. Overall, we find that while interior wind profiles that do not resemble the cloud level are possible, they are statistically unlikely. Finally, inspired by the Juno microwave radiometer measurements, assuming the brightness temperature is dominated by the ammonia abundance, we find that depth‐dependent flow profiles are still compatible with the gravity measurements.

Photospheric Polarization Signatures from Long Gamma-Ray Burst Simulations

Abstract A comprehensive understanding of gamma-ray bursts (GRBs) has been elusive due to the variety of questions surrounding the radiation mechanism at play in these events. Polarization measurements of GRBs can heavily constrain the relevant radiation mechanisms and the structure of the GRB jet; however, there is a limited number of theoretical predictions that observed GRB polarizations can be compared against. Here, we conduct radiative transfer calculations of a set of two-dimensional relativistic hydrodynamic long GRB (LGRB) jet simulations, of a constant and a variable jet, using the Monte Carlo Radiation Transport (MCRaT) code. MCRaT has been enhanced by the inclusion of polarization; it has been first verified by reproducing a variety of results in the literature and then used to obtain the time-integrated and time-resolved polarization degrees and angles of the synthetic LGRBs. While the obtained time-integrated polarization degrees (≲1%) are consistent with the constraints from the POLAR experiment, they are lower than other theoretical studies due to the lack of strong gradients in the model jet profiles that we use. The time-resolved results suggests that GRBs with wide jets observed on axis will have small polarization degrees (≲2%) and constant polarization angles, during the brightest portion of the light curve. GRBs observed off-axis will have larger polarization degrees and polarization angles that change with the temporal structure of radiating shells in the outflow. We then place our results in the context of GRB prompt emission models and future LEAP and POLAR-2 GRB polarimetry detections.

Scaling of L-mode heat flux for ITER and COMPASS-U divertors, based on five tokamaks

This contribution aims to improve existing scalings of the L-mode power decay length , especially for plasma configurations with strike points at the ITER-relevant location—closed vertical divertor targets. We propose 13 new scalings based on data from the tokamaks JET, EAST, MAST, Alcator C-mod and COMPASS, and validate them against the output of the 2D turbulence code HESEL. The analysis covers 500 divertor heat flux profiles (obtained by probes or IR cameras), measured in L-mode discharges with varying 12 global plasma parameters (all well predictable). We find that the two previously published scalings (Eich 2013 J. Nucl. Mat. 438 S72) and (Scarabosio 2013 J. Nucl. Mat. 438 S426), which were based on outer target data from AUG and JET, describe the JET, C-mod and COMPASS profiles well. This holds not only at the outer horizontal and vertical targets, but surprisingly also at the inner vertical targets. In contrast, EAST, HESEL and especially MAST data are poorly described by these two scalings. We therefore derive 13 new scalings, which account for 85–92 % of the measured variability across all five tokamaks. Although each of the scalings is based on a different parameter combination, their predictions for the ITER and COMPASS-Upgrade tokamaks are very similar. Just before the L-H transition in the ITER baseline scenario, the presented scalings predict values mm. For the COMPASS-Upgrade tokamak, all the scalings predict mm with a single exception of the scaling based on the stored plasma energy which predicts only 1.2 mm for both tokamaks. We encourage the reader to use as many of these scalings as possible, depending on available data. In attached plasma and using significant assumptions, our results imply steady-state surface-perpendicular heat flux around 10 MW/m2 for ITER, and 20 MW/m2 for COMPASS-Upgrade.

Numerical simulation of jet mode in electrospraying of Newtonian and viscoelastic fluids

This study aims to model the role of the viscoelastic properties of polymeric solutions in the jet mode of the electrospray process numerically. For this purpose, first, the computational challenges in front of a numerical investigation of such complex physics are explained, and the recent advances in rectifying these problems, especially the high Weissenberg instability, is described. Then, a numerical procedure based on the Log-conformation method (LCM) is introduced, and several numerical simulations are performed to model the behavior of electrified Newtonian and viscoelastic jets. In the first step, the discrete model for the LCM equations is validated by simulating the benchmark problem of the sedimenting sphere. The obtained results show that the proposed algorithm can improve the previous Weissenberg threshold reported for a stable solution. Then, an electrified deionized (DI) water jet is simulated, and the obtained jet profile is compared with the experimental data. Finally, the proposed algorithm is used to simulate viscoelastic electrified jets, where the effect of the Weissenberg number (Wi) on the jet profile is examined. In agreement with the previously obtained experimental results, the numerical results show that by increasing the solution concentration, the asymptotic jet profile is reached at a smaller length from the nozzle, while the final thickness of the jet is slightly reduced.

Exploring a new method to obtain the 3D abrasive water jet profile

As high-pressure water combined with abrasive particles together comes out from a nozzle, a high-energy abrasive water jet beam is formed. And this high-energy water jet beam could be used as a sharp knife to cut all types of material. Different from a rigid knife, whose profile is fixed, this high-energy beam’s profile is changing as the cutting parameters change. Therefore, if this knife is used to cut a workpiece accurately and precisely, the knife’s profile under each set of cutting conditions has to be searched out. And further, based on the jet profile, compensation on the jet profile has to be carried out. In the past, a 2D model for the kerf profile cut by jet has been built; then, compensation on the jet based on the 2D model of the kerf profile has been carried out. However, using a 2D model to describe a 3D profile is definitely not enough. In this paper, a new method generating a 3D kerf profile through scanning an integrated sample has been provided. With this method, complete 3D abrasive water jet profiles under each cutting conditions could be obtained through the kerf profiles. With these precise 3D abrasive water jet profiles, better compensating the cutting errors becomes possible in future.

The influence of deep jets on Jupiter's weather layer in a 1.5‐layer shallow‐water model

AbstractThe depth of the jet streams seen in Jupiter's outer weather layer has long been debated, with alternative suggestions of confinement to the weather layer and extensions deep into the planet being considered. Interpretation of measurements from NASA's Juno probe have suggested that weather‐layer jets do extend deep into the planet, down to depths of (3,000 km). However, this relies on the assumption that the jet profile does not change its spatial structure with depth, which may not be the case. In this work, we consider a simple 1.5‐layer shallow‐water model of Jupiter‐like jet streams, with prescribed deep jets in the lower layer, and look at the parameters affecting the strength of the coupling between the layers. We find the value of the Rossby deformation scale, L D, to be particularly important, not just in setting the magnitude of variations in layer depth, but also in dictating the effectiveness of radiative damping. We also find the radiative damping timescales, the energy injection rate, and the spacing of deep jets to be important. We combine these findings into our best‐guess simulations of the real Jupiter and find that low latitudes are relatively uncoupled between the layers, with high latitudes being more tightly coupled. These effects can be tied to the smallness of Jupiter's L D and the effectiveness of radiative damping as a coupling mechanism. These simulations do, however, produce equatorial subrotation and eddy‐momentum fluxes unlike those on the real planet. It may be, therefore, that spatially varying forcing and very long radiative damping timescales are required for this model to be more Jupiter‐like.

An asymptotic-numerical comparative study for axisymmetric free surface liquid jet near and far from exit at high Reynolds number

Purpose The purpose of this study is to examine theoretically the axisymmetric flow of a steady free-surface jet emerging from a tube for high inertia flow and moderate surface tension effect. Design/methodology/approach The method of matched asymptotic expansion is used to explore the rich dynamics near the exit where a stress singularity occurs. A boundary layer approach is also proposed to capture the flow further downstream where the free surface layer has grown significantly. Findings The jet is found to always contract near the tube exit. In contrast to existing numerical studies, the author explores the strength of upstream influence and the flow in the wall layer, resulting from jet contraction. This influence becomes particularly evident from the nonlinear pressure dependence on the upstream distance, as well as the pressure undershoot and overshoot at the exit for weak and strong gravity levels, respectively. The approach is validated against existing experimental and numerical data for the jet profile and centerline velocity where good agreement is obtained. Far from the exit, the author shows how the solution in the diffusive region can be matched to the inviscid far solution, providing the desired appropriate initial condition for the inviscid far flow solution. The location, at which the velocity becomes uniform across the jet, depends strongly on the gravity level and exhibits a non-monotonic behavior with respect to gravity and applied pressure gradient. The author finds that under weak gravity, surface tension has little influence on the final jet radius. The work is a crucial supplement to the existing numerical literature. Originality/value Given the presence of the stress singularity at the exit, the work constitutes a superior alternative to a computational approach where the singularity is typically and inaccurately smoothed over. In contrast, in the present study, the singularity is entirely circumvented. Moreover, the flow details are better elucidated, and the various scales involved in different regions are better identified.

A phase averaged PIV study of circular and non-circular synthetic turbulent jets issuing from sharp edge orifices

An extensive experimental study using Particle Image Velocimetry (PIV) on synthetic jets issuing from different orifice shapes is reported. All data are phase and time averaged to derive mean velocity, half-velocity width and rms velocity profiles in the near field of the jet (0 < X/D < 7), at a Reynolds number around 10,000. Different non-circular orifice shapes as rectangular, square, elliptic and triangular are considered and results are compared to those of the circular orifice in order to investigate the effect of asymmetry on the turbulent flow field in view of mixing enhancement. The measurements are carried out on two orthogonal planes to capture three dimensional features of non-circular jets. Results show highest velocity decay rate for elongated orifices, especially the rectangular one, in comparison to the circular one, both in phase and time-averaged plots. Time averaged results show higher velocity decay rate of synthetic jets in comparison to those of continuous ones. It is also observed that, for X/D > 5, only profiles of circular and square jets become partially self-similar. For synthetic jets, higher turbulence content is measured for all orifice shapes at the centerline and close to the orifice exit in comparison to continuous jets.

Experimental investigation of electrohydrodynamic modes in electrospraying of viscoelastic polymeric solutions

The main aim of this study is to explore the role of viscoelastic properties of polymeric solutions on mode transitions in the electrospray process. By adjusting the applied electric potential between the nozzle and the collecting substrate, various electrohydrodynamic (EHD) modes were photographed by using a high-speed camera. Then, the effect of operating parameters on the droplet size in the dripping mode and the jet profile in the jet mode was investigated. By categorizing the EHD modes of each viscoelastic solution into dimensionless operating maps, it can be seen that by increasing the solution concentration, the extents of dripping mode and beads-on-a-string structure dwindle, while the jet stabilizes in a wider range of electric capillary numbers. Furthermore, contrary to deionized water, when the applied voltage escalates, the stick jet mode is observed where the jet sticks to the outer surface of the nozzle and the asymptotic thickness of the jet falls.