Pattern Of Jets Research Articles

Particle-scale modeling study of coaxial jets of gas-solid swirling flow in an industrial-scale annular pipe via CFD-DEM

In this work, the gas-solid swirling flow characteristics of coaxial jets in an industrial-scale annular pipe with a helical swirler is numerically simulated via the CFD-DEM. After validating the numerical model, the general flow pattern of coaxial jets, and gas-particle mixing behavior together with the particle-scale information are discussed. The effect of the geometry parameters of the swirler is studied and analyzed in terms of particle azimuthal velocity and particle Reynolds number. The results demonstrate that the presence of the swirler enhances both the turbulent disturbance and gas vorticity. Increasing vane angle and diameter of swirler is beneficial for the particle dispersion. The particle velocity slightly reduces with decreasing the height in the region 0.6 m < H < 0.7 m but dramatically increases with decreasing the height in the region of height H < 0.6 m. The entrainment of particles by the swirling flow increases the distribution width and azimuthal velocity of particles with decreasing the height.

Aeroacoustic characteristics of supersonic offset jets

The offset jet configuration is one where the jet is discharged at some distance from a solid surface. Although the geometric configuration may look simple, the flow may involve several complexities. In propulsion systems, the high-speed jet generated from the rear engine of an aircraft, flowing nearby the fuselage, can be treated as an offset jet. In this work, an experimental investigation of the interaction noise due to circular high-speed offset jets is performed in an anechoic environment at different nozzle pressure ratios and offset ratios (height of the jet centerline above the plate per nozzle width). A large horizontal plate placed over a height-adjustable stand is used as the offset plate. Acoustic characteristics such as overall sound pressure level and the directivity pattern of free and offset jets are compared for different nozzle pressure ratios. The effect of offset ratio on noise characteristics is also investigated. Flow visualization is also carried out to understand the shock structure and its noise generation mechanism. Acoustic characteristics reveal that noise levels are higher for an offset jet compared to a free jet. Sound pressure levels for offset ratio 0.5 are lower than those for other offset ratios. The noise levels are higher for offset ratio 1.0 due to the presence of feedback tone. Schlieren visualization studies also corroborate the above characteristics.

A Study of QCD Radiation in VBF Higgs Production with Vincia and Pythia

We discuss and illustrate the properties of several parton-shower algorithms available in Pythia and Vincia, in the context of Higgs production via vector boson fusion (VBF). In particular, the distinctive colour topology of VBF processes allows to define observables sensitive to the coherent radiation pattern of additional jets. We study a set of such observables, using the Vincia sector-antenna shower as our main reference, and contrast it to Pythia's transverse-momentum-ordered DGLAP shower as well as Pythia's dipole-improved shower. We then investigate the robustness of these predictions as successive levels of higher-order perturbative matrix elements are incorporated, including next-to-leading-order matched and tree-level merged calculations, using Powheg Box and Sherpa respectively to generate the hard events.

The CFD simulation of reactive flow in parallel flow regenerative shaft kilns using porous media model

Understanding the flow pattern of the gas jets in packed beds can have considerable significance in improving reactor design and process optimization. This study researches the fuel diffusion in the radial direction and the flame length in a packed bed of a parallel flow regenerative shaft kiln. This kiln is characterized that the fuel is injected vertically in the packed bed using a lot of lances in the cross-section while the combustion air is distributed continuously. Such a large, packed bed has to be approximated as a porous media. This assumption is used to model the reactive flow in the kilns. Using a box with 700 spheres of 52 mm spheres in body-centered cube arrangement the local concentrations of injected nitrogen in air-flow were measured. The measured values match approximately with those calculated with the porous media model. The studied parameters are the number of burners and burner arrangements. The radial mixing of fuel and air in a packed bed is relatively bad. Therefore, a lot of burners are needed for better temperature homogenization in the cross-section

Cylinders and jets in crossflow: Wake formations as a result of varying geometric proximities

The combined flow physics of several canonical flow configurations is experimentally studied. Here, we analyze an array of jets issuing into a crossflow, then immediately navigating past an array of cylinders. This is achieved with a 2 × 3 triangular pattern of jets and symmetric cylinders at three jets to crossflow velocity ratios, enabling near-complete optical access of each jet, with velocities measured by time-resolved particle image velocimetry. Jet trajectories reveal that each configuration adheres to a power-law trend and that greater penetration is achieved by the downstream and confined jets compared to the more conventional upstream one. Recirculation regions of the upstream and downstream jets are nearly independent, with the confined jet encompassing regions of overlap with both. Turbulent statistics reveal the influence of geometric placement and velocity ratio on the time-averaged velocity, anisotropy, and Reynolds stresses incurred by each jet. Galilean decomposition utilizes a supplemental crossflow-only velocity field to delineate the influence of each jet's low- and high-pressure regions on the otherwise uniform stream. Proper orthogonal decomposition suggests that increased jet penetration decreases the number of modes required for truncation in the investigated spanwise plane. Vortex identification algorithms are applied to the reconstructed flow fields, reaffirming that with increasing velocity ratio, the jets generate vortices of their own in similar statistical formations as the cylinders. This investigation provides a foundation to aid future modeling efforts toward characterizing flow physics of importance in designing and passively controlling transverse jets with varying blockage proximities in a crossflow.

CONTRIBUTION OF NON-ISOTHERMAL JETS TO THE PROCESSES OF NOISE GENERATION OF ENERGY MACHINES WHEN INSTALLING SILENCERS

The method of James Lighthill is known and widely used, which allows determining the acoustic power of isothermal jets. A mathematical model for calculating the acoustic parameters (sound power, radiation pattern) of non-isothermal sound jets is proposed, taking into account the noise silencer installed in the gas exhaust tract. At the output, the equations of continuity, the amount of motion, energy, as well as the Lighthill wave equation are used. A statistical model is used as a turbulence model for calculations. A physical mechanism of noise generation by turbulent flows is proposed, which consists in considering "own" and "shear" noise. The " own " noise is caused by turbulent pulsations of the gas-dynamic flow, the "shift" noise is caused by the presence of a flow velocity gradient. Analytical dependences of the components of "own" and "shift" noise are obtained.

Visualizing Properties of a Quadratic Function Using Torricelli’s Fountain

In the same chapter of his book Opera Geometrica, Torricelli published two discoveries: 1) initial velocity of a jet from a container increases with the square root of the depth of the hole; 2) he drew the pattern of jets from three openings at the wall of a container filled with water to constant level H and determined the height of the hole with maximal range. In studying the pattern, Torricelli used the mentioned law of initial velocities and Galileo’s law of free fall and projectile motion. The first Torricelli discovery is now well known in physics education under the name Torricelli’s law. But the pattern of jets from a container entered into physics literature along two ways, which we propose to name “da Vinci’s way” and “Torricelli’s way.” Along “da Vinci’s way” educators and textbook authors (Ref. 2 and textbooks and articles cited by Biser and Atkin) present incorrect drawings of jets in order to incorrectly “demonstrate” the correct Torricelli’s law. Along “Torricelli’s way” educators point out that the shape and range of a jet depend on the initial velocity as well as on the time of flight of a jet. Using algebra and calculus (instead of geometry, proportions, and narrative used by Torricelli and Galileo) the shape of trajectories, their envelope, range, and meeting of two jets at an arbitrary datum level are determined by quadratic function and quadratic equation. Their detailed mathematical analysis is presented in this paper.

Tandem electrospinning for heterogeneous nanofiber patterns

Smart nanofibrillar constructs can be a promising technological solution for many emerging and established fields, facilitating the potential impact of nano-scale strategies to address relevant technological challenges. As a fabrication technique, electrospinning (ESP) is relatively well-known, accessible, economic, and fast, though until now has shown limitation over control and design of the fibrillar constructs which can be produced. Here, we introduce ‘Tandem Electrospinning’ (T-ESP), a novel technique able to create increasingly complex patterns of fibrous polymeric constructs on a micro and nano-scale. Modifying a standard ESP configuration results in a focusing electric field that is able to spatially define the deposition pattern of multiple polymer jets simultaneously. Additional spatially defined heterogeneity is achieved by tuning polymer solution properties to obtain a gradient of fiber alignment. Heterogeneous fibrous meshes are created with either random, aligned, or a divergent fiber patterns. This approach holds potential for many fields, with application examples shown for tissue engineering and separation technologies. The technique outlined here provides a rapid, versatile, and accessible method for polymeric nanofabrication of patterned heterogeneous fibrous constructs. Polymer properties are also shown to dictate fiber alignment, providing further insight into the mechanisms involved in the electrospinning fabrication process.

An experimental study on the effect of square grooves on decay characteristics of a supersonic jet from a circular nozzle

In this experimental work, the effect of square grooves on the structure of a supersonic jet emanating from a circular nozzle has been investigated at three different nozzle inlet total pressures i.e 360 kPa, 550 kPa and 720 kPa. The nominal exit Mach number is 1.8. A new empirical relation for predicting the supersonic core length for grooved nozzle has been suggested. Further, a new parameter “groove effectiveness” has also been suggested to quantify the effect of the groove by using the total pressure data in the supersonic core length. Experimental results suggest that at higher nozzle inlet total pressure, the groove effectiveness plays a minor role. From the jet centreline total pressure data, supersonic core length, the locations at which 50 % and 90 % decay occurs have been obtained. It has been observed that higher groove effectiveness is associated with smaller values of supersonic core length, L50% and L90%. Schlieren images of the jet structure shows unsymmetrical shock pattern of jets emanating from a single grooved nozzle.

Observation of Electrospinning Behavior of Nanoscale Fibers by a High-Speed Camera

Electrospinning is regarded as an effective method to generate nanoscale fibers. However, we believe that the mechanism of the formation of nanoscale fibers by Electrospinning has not yet been fully investigated. In this study, the jet behavior under various conditions was observed with a high-speed camera with short exposure periods. The behaviors of stable and unstable jets were compared. The effect of bending instability on the deposition pattern of jets was examined at different voltages and concentrations. In addition, the diameters of nanoscale fibers were analyzed as a function of sampling position.

Characteristics of the Velocity Distribution in a Hydraulic Jump Stilling Basin with Five Parallel Offset Jets in a Twin-Layer Configuration

The flow structure of vertical and horizontal planes in a stilling basin with five parallel offset jets in a twin-layer configuration for four offset ratios (S1/h=1,2,3,4) has been investigated. The velocity distribution was measured, processed, and subsequently used to characterize the flow structure. The flow pattern in the stilling basin exhibits a mixing flow pattern of jets and hydraulic jumps. As the downstream water depth increases in the stilling basin, five different flow patterns appear successively: free jets, hydraulic jumps, submerged jets and hydraulic jumps, mixed submerged jets and critical jumps, and mixed submerged jets and submerged jumps. The results indicate that the velocity distributions in the vertical and horizontal planes of the lower-layer orifices and in the potential core region of the upper-layer orifices are similar to the classical jet; in other regions, the velocity distribution is similar to the hydraulic jump. In addition, the energy dissipation ratio increases with the increasing Froude number, with a value of greater than 70% at F>8.0. The energy dissipation ratio in the stilling basin with five parallel offset jets in a twin-layer configuration is, on average, 5% larger than that of the SBJ basin and 13% larger than that of the classical jump basin.

The origin of Phobos grooves from ejecta launched from impact craters on Mars: Tests of the hypothesis

The surface of the martian moon Phobos is characterized by parallel and intersecting grooves that bear resemblance to secondary crater chains observed on planetary surfaces. Murray (2011) has hypothesized that the main groove-forming process on Phobos is the intersection of Phobos with ejecta from primary impact events on Mars to produce chains of secondary craters. The hypothesis infers a pattern of parallel jets of ejecta, either fluidized or solidified, that break into equally-spaced fragments and disperse uniformly along-trajectory during the flight from Mars to Phobos. At the moment of impact with Phobos the dispersed fragments emplace secondary craters that are aligned along strike corresponding to the flight pattern of ejecta along trajectory. The aspects of the characteristics of grooves on Phobos cited by this hypothesis that might be explained by secondary ejecta include: their observed linearity, parallelism, planar alignment, pitted nature, change in character along strike, and a “zone of avoidance” where ejecta from Mars is predicted not to impact (Murray, 2011).To test the hypothesis we plot precise Keplerian orbits for ejecta from Mars (elliptical and hyperbolic with periapsis located below the surface of Mars). From these trajectories we: (1) set the fragment dispersion limits of ejecta patterns required to emplace the more typically well-organized parallel grooves observed in returned images from Phobos; (2) plot ranges of the ejecta flight durations from Mars to Phobos and map regions of exposure; (3) utilize the same exposure map to observe trajectory-defined ejecta exposure shadows; (4) observe hemispheric exposure in response to shorter and longer durations of ejecta flight; (5) assess the viability of ejecta emplacing the large family of grooves covering most of the northern hemisphere of Phobos; and (6) plot the arrival of parallel lines of ejecta emplacing chains of craters at oblique incident angles. We also assess the bulk volume of ejecta from martian impact events and the number of events that are necessary to supply sufficient bulk densities of secondary impactor fragments.On the basis of our analysis, we find that six major predictions of the Murray hypothesis are not consistent with a wide range of Mars ejecta emplacement models and observations as follows: (1) To emplace families of parallel grooves as observed in the most common features (grooves that manifest virtually no positional defects), and to reach the maximum geographic extent of Phobos, grid patterns of ejecta fragments must be produced with nearly identical diameters (often tens of thousands in number) and must launch with virtually zero rates of dispersion (<1mm/s and <1.0μrad in all degrees of freedom) into fixed patterns of arrays where fragment dispersion is referenced to a common datum point for the duration of flights from Mars to Phobos of up to 3h. (2) Half of the areal region observed as a “zone of avoidance” (where grooves are absent on the trailing orbital apex of Phobos) is directly exposed to ejecta trajectories from the surface of Mars, which suggests that the “zone of avoidance” is unrelated to ejecta trajectories. (3) Several families of grooves display groove segments that are observed in a region of Phobos that is shadowed from martian ejecta trajectories for flight durations up to 3h. Where the Murray hypothesis predicts the emplacement of groove families from a single ejecta plume, this strongly suggests that these families of grooves could not have been produced by martian impact ejecta. (4) To reach increasingly westerly locations of Phobos ejecta must travel in space for substantially longer flight times (up to 20X) which would produce substantially lower secondary crater densities on the anti-Mars side of Phobos and observably reduce their pit organization. This is not observed. (5) The largest family of grooves cannot be emplaced by any valid trajectory from Mars in its present day or ancient orbit. (6) If emplaced by grid patterns of ejecta, the irregular topography and small-body radius of Phobos would clearly disrupt groove family linearity and parallelism due to the preponderance of oblique incident angle impacts. However, when viewed from any position, the vast majority of groove families and individual grooves appear to completely avoid the effects of Phobos' morphology. Based on our analysis we conclude that the Murray hypothesis, that many Phobos grooves are formed by intersection of ejecta from craters on Mars, is not valid.

Dance of the microswimmers

From gut-inhabiting bacteria to sea-dwelling algae, microorganisms display a penchant for coordinated movement. Nonlinear dynamics and fluid mechanics can help explain the curious behavior.

Jet characterization in the upper troposphere/lower stratosphere (UTLS): applications to climatology and transport studies

Abstract. A method of classifying the upper tropospheric/lower stratospheric (UTLS) jets has been developed that allows satellite and aircraft trace gas data and meteorological fields to be efficiently mapped in a jet coordinate view. A detailed characterization of multiple tropopauses accompanies the jet characterization. Jet climatologies show the well-known high altitude subtropical and lower altitude polar jets in the upper troposphere, as well as a pattern of concentric polar and subtropical jets in the Southern Hemisphere, and shifts of the primary jet to high latitudes associated with blocking ridges in Northern Hemisphere winter. The jet-coordinate view segregates air masses differently than the commonly-used equivalent latitude (EqL) coordinate throughout the lowermost stratosphere and in the upper troposphere. Mapping O3 data from the Aura Microwave Limb Sounder (MLS) satellite and the Winter Storms aircraft datasets in jet coordinates thus emphasizes different aspects of the circulation compared to an EqL-coordinate framework: the jet coordinate reorders the data geometrically, thus highlighting the strong PV, tropopause height and trace gas gradients across the subtropical jet, whereas EqL is a dynamical coordinate that may blur these spatial relationships but provides information on irreversible transport. The jet coordinate view identifies the concentration of stratospheric ozone well below the tropopause in the region poleward of and below the jet core, as well as other transport features associated with the upper tropospheric jets. Using the jet information in EqL coordinates allows us to study trace gas distributions in regions of weak versus strong jets, and demonstrates weaker transport barriers in regions with less jet influence. MLS and Atmospheric Chemistry Experiment-Fourier Transform Spectrometer trace gas fields for spring 2008 in jet coordinates show very strong, closely correlated, PV, tropopause height and trace gas gradients across the jet, and evidence of intrusions of stratospheric air below the tropopause below and poleward of the subtropical jet; these features are consistent between instruments and among multiple trace gases. Our characterization of the jets is facilitating studies that will improve our understanding of upper tropospheric trace gas evolution.

Heat transfer measurements for jet impingement arrays with local extraction

Impingement heat transfer using an array of jets can produce very high average heat transfer coefficients if the jets are closely spaced and if the spent fluid is removed through effusion holes shortly after impingement. This study measured heat transfer for a compact staggered array pattern of impingement jets with an inter-jet spacing of 2.34 jet diameters. Six local effusion holes ( d eff / d jet = 0.6) surrounded each jet so that impinging air was extracted locally through the same plane as the jets. Three scaled models were tested with jet diameters ranging from d = 0.94–8.46 mm, at a total Reynolds number range of Re d = 500–10,000. A combined Nu vs. Re correlation of Nu d = 0.36 Re d 0.59 was found for a jet-to-target spacing of 1 jet diameter. Jet-to-target height was varied from 0.44 to 3.97 jet diameters, and increasing jet-to-target spacing was found to decrease average heat transfer in all cases tested. The smaller scale arrays gave higher dimensional heat transfer coefficients as h varied with the −0.41 power of the diameter for fixed jet velocity and jet-to-target spacing. Heat transfer coefficients of nearly 900 W/m 2 K were achieved over an 8.5 cm 2 area using the smallest scale array. Overall pressure drop coefficients of approximately seven were measured.

Three-dimensional Compressible Flow Simulation of Top-blown Multiple Jets in Converter

A three-dimensional mathematical model has been developed to simulate the compressible jets flow from the top-blown lance with multi-nozzles in converter to a free surrounding domain. The variations of fluid density and viscosity, high temperature, and Mach number were taken into consideration in this model which was validated against the physical modeling results. More specifically, computations were obtained to compare the widely used realizable k-epsilon turbulence model against the standard k-omega turbulence model, which shows that the latter one is superior to calculate diverse turbulent conditions within the multiple jets. Moreover, the coalescence pattern of the multiple jets has been illustrated by their Mach number distribution, and each individual jet proceeds in a curve course, bending to the lance center and tending to unite. The effects of the inclination angles on the jets coalescence were also investigated, which indicates that the lower the inclination angle is, the stronger the interfering extent between the multiple jets is. With the help of this model, the dynamic power of the multiple jets to support the cavity formation was demonstrated, and additionally, a mathematical model concerning the effective penetration radius and digressing path of the multiple jets was proposed by taking the inclination angle and the axial distance from the nozzle tips as arguments.

Flow pattern, periodicity and energy dissipation in a batch rotor–stator mixer

The flow pattern and the distribution of energy dissipation rate in a batch rotor–stator mixer have been investigated. Sliding mesh and standard k–ɛ turbulence model were employed to predict velocity and energy dissipation rate distributions verified experimentally by the Laser Doppler Anemometry measurements. The agreement between predicted and measured bulk flow field as well as the flow pattern of jets emerging from the stator holes was very good. Results showed that the periodicity of the jet can be related to the rotor's velocity and number of blades. The energy balance based on measured velocity distribution indicated that about 70% of energy is dissipated in close proximity to the mixing head. Both simulation and measurement showed that the jet velocity and flowrate through the holes were proportional to N while the energy dissipation rate scaled with N3.

Two- and three-particle azimuthal correlations of high-pt charged hadrons in Pb–Au collisions at 158 A GeV/c

Azimuthal correlations of hadrons with high transverse momenta serve as a measure to study the energy loss and the fragmentation pattern of jets emerging from hard parton–parton interactions in heavy-ion collisions. Preliminary results from the CERES experiment on two- and three-particle correlations in central Pb–Au collisions are presented. A strongly non-Gaussian shape on the away-side of the two-particle correlation function is observed, indicating significant interactions of the emerging partons with the medium. Mechanisms like deflection of the initial partons or the evolution of a mach cone in the medium can lead to similar modifications of the jet structure on the away-side. An analysis based on three-particle correlations is presented which helps us to shed light on the origin of the observed away-side pattern.

Ischemic mitral regurgitation: Mechanisms and echocardiographic classification

Chronic ischemic mitral regurgitation (IMR) is a common complication of myocardial infarction and severely affects cardiovascular mortality and morbidity. Multiple pathophysiologic mechanisms, such as left ventricular (LV) remodeling and dysfunction, annular dilation/dysfunction, and mechanical dyssynchrony, are involved in generating IMR, each of them having different weight. However, the prerequisite to initially creating regurgitation is the presence of local or global LV remodeling that alters the geometrical relationship between the ventricle and valve apparatus. In the wide spectrum of patients with chronic IMR, the assessment of some echocardiographic parameters, such as tethering pattern, leaflet motion, origin and direction of the regurgitant jets, allows one to identify different specific subgroups of patients subjected to different therapeutic approaches. The aim of medical and/or surgical therapy is to ameliorate heart failure symptoms, and improve LV remodeling and function and the intermediate/long-term outcome. The targets of surgical MV repair involve annulus, leaflets, chordae and ventricles. The restricted annuloplasty is the most commonly adopted surgical procedure that improves heart failure symptoms but not survival when compared to medical therapy and is also subject to a high incidence of late failure (approximately 30%). There are some preoperative echocardiographic predictors of failure that include valve (degree of valve remodeling, jet characteristics), ventricular (degree of remodeling, diastolic dysfunction) and surgical factors.

Experimental study on hydrodynamic behaviors of high-speed gas jets in still water

The present paper describes experimental investigation on the flow pattern and hydrodynamic effect of underwater gas jets from supersonic and sonic nozzles operated in correct- and imperfect expansion conditions. The flow visualizations show that jetting is the flow regime for the submerged gas injection at a high speed in the parameter range under consideration. The obtained results indicate that high-speed gas jets in still water induce large pressure pulsations upstream of the nozzle exit and the presence of shock-cell structure in the over- and under-expanded jets leads to an increase in the intensity of the jet-induced hydrodynamic pressure.