Types Of Jets Research Articles

Theoretical and experimental investigation of wall confluent jets ventilation and comparison with wall displacement ventilation

This paper reports CFD and experimental results of the characteristics of wall confluent jets in a room. The results presented show the behaviour of wall confluent jets in the form of velocity profiles, the spreading rate of jets on the surface, jets decay, etc. The empirical equations derived are compared with other types of air jets. In addition, the flow in wall confluent jets is compared with the flow in displacement ventilation supply, with regards to the vertical and horizontal spreading on the floor. It is concluded that the jet momentum of wall confluent jets can be more conserved than other jets. Thus, wall confluent jets have a greater spread over the floor than displacement flow.

Very Light and Fast

This article focuses on the developments in materials, production methods, and turbine designs that have spawned a new class of jets. Cessna’s Citation Mustang became the first very light jet to reach commercialization. According to market leaders, the development of computerized cockpits with simplified displays has also been huge. Composites also let engineers combine lots of parts—panels, framing, rivets—into a single part. The fewer parts, the easier and cheaper it is to assemble and the more reliable the finished airplane. Every aerospace company is looking for bolt-on components that simplify assembly and maintenance. Adam Aircraft seeks to simplify production by making large composite parts. The second mechanical advance that makes very light jets possible is the compact, reliable turbofan. While Pratt is well-known for huge turbines that power commercial passenger jets, the company produces several small turbines. Pratt uses blisks and other technologies to simplify production. The result is a new type of jet, one that makes jet airplanes far more affordable.

Modeling study on the characteristics of laminar and turbulent argon plasma jets impinging normally upon a flat plate in ambient air

Modeling study is performed to compare the flow and heat transfer characteristics of laminar and turbulent argon thermal-plasma jets impinging normally upon a flat plate in ambient air. The combined-diffusion-coefficient method and the turbulence-enhanced combined-diffusion-coefficient method are employed to treat the diffusion of argon in the argon–air mixture for the laminar and the turbulent cases, respectively. Modeling results presented include the flow, temperature and argon concentration fields, the air mass flow-rates entrained into the impinging plasma jets, and the distributions of the heat flux density on the plate surface. It is found that the formation of a radial wall jet on the plate surface appreciably enhances the mass flow rate of the ambient air entrained into the laminar or turbulent plasma impinging-jet. When the plate standoff distance is comparatively small, there exists a significant difference between the laminar and turbulent plasma impinging-jets in their flow fields due to the occurrence of a large closed recirculation vortex in the turbulent plasma impinging-jet, and no appreciable difference is found between the two types of jets in their maximum values and distributions of the heat flux density at the plate surface. At larger plate standoff distances, the effect of the plate on the jet flow fields only appears in the region near the plate, and the axial decaying-rates of the plasma temperature, axial velocity and argon mass fraction along the axis of the laminar plasma impinging-jet become appreciably less than their turbulent counterparts.

Jet stream patterns over Europe in the period 1950–2001 – classification and basic statistical properties

Primary goal of presented study is to classify the most frequent patterns of the upper tropospheric jet stream over Europe. Wind fields were grouped into separated classes with the help of the correlation-based Lund’s technique. The treatment of vector fields with Lund’s method was achieved by replacement linear Pearson coefficient with vector correlation coefficient. The outstanding features of the upper-level circulation and ground-based weather associated with each jet type were analysed. Finally, basic statistics of jet stream patterns (frequency, duration time, day-to-day changes of jet structure) as well as their trends were estimated. The analysis was conducted on the basis of mean daily wind components at 200 hPa level, air temperature at 850 hPa, sea-level pressure, vertical velocity and geopotential at 500 hPa level. Data set was extracted from the NCEP/NCAR Reanalysis. The warm half-year in the period 1950–2001 was taken into consideration. The first 15 most frequent jet types, including 60.8% of the sample, were selected. Three jet stream types (C, E and I) are associated with distinct temperature changes in western Europe. Another three types (B, F and O) cause significant thermal advection in eastern and central Europe. Seasonal differences in frequency and duration time of jet stream patterns are also observed. Meridional types (A, C and D) dominate in spring, while in summer, patterns with intensified zonal flow prevail (B, E and J). At last, it is worth noticing that the majority of selected jet types pronounce an increase in day-to-day changes of wind field, which may indicate slight enhancement of circulation dynamics in the upper troposphere.

Climatology of Barrier Jets along the Alaskan Coast. Part I: Spatial and Temporal Distributions

Abstract This paper investigates the temporal and spatial climatology of coastal barrier jets in the Gulf of Alaska. The jets are divided into two categories based upon the origin of the air involved: “classic” barrier jets fed primarily by onshore flow and “hybrid” jets fed primarily by gap flow from the continental interior. The analyses are compiled from five years (1998–2003) of synthetic aperture radar images from the Radarsat-1 satellite totaling 3000 images. Thermodynamic and kinematic data from the NCEP reanalysis is used in the interpretation of the results. The majority of coastal barrier jets occur during the cool season, with the coastline near Mount Fairweather and the Valdez–Cordova mountains experiencing the greatest number of barrier jets. Hybrid jets are even more strongly restricted to the cool season and are commonly found to the west of Cross Sound, Yakutat Bay, and Icy Bay. Some interannual variability in the total number of jets is observed. Coastal barrier jet formation is associated with onshore wind directions and maximum terrain heights exceeding 2 km within 100 km of the coast, features that support low-level flow blocking. Hybrid jet formation requires the additional condition of an abnormally large offshore-directed pressure gradient force. Half of the barrier and hybrid jets exhibit surface wind speeds in excess of 20 m s−1 (strong gale), although their widths are typically less than 100 km. The maximum speed of both types of jet tends to be 2–3 times that of the ambient synoptic flow. A small percentage of the jets detach from the coastline, with the typical detachment distance being 10 km.

Electric current as a control variable in the electrospinning process

In the electrospinning process submicron-diameter polymer fibers can be produced when a high potential difference is applied to a polymer drop suspended at the tip of a capillary. The electrospinning process is affected by a wide range of parameters, because of which controlling the properties of the fibers is difficult. This is the major hurdle in the development of practical applications of electrospun fibers along with its low productivity. Here we are proposing to use the electric current in the electrospinning process to control the “quality of the fibers”. Electrospinning of a solution of polyacrylonitrile in dimethylformamide (PAN/DMF) was done by applying a programmed variable flow rate at different constant voltages. The electric current in the process was measured in real time. Four types of jet regimes were observed, electric current and the morphology of the fibers corresponding to these regimes were analyzed. A relation between the electric current, type of jet and morphology of the fibers has been established. The mechanical properties of electrospun fiber mats were also measured by a tensile testing method. POLYM. ENG. SCI. 46:954–959, 2006. © 2006 Society of Plastics Engineers

Simulation of equatorial and high-latitude jets on Jupiter in a deep convection model

The bands of Jupiter represent a global system of powerful winds. Broad eastward equatorial jets are flanked by smaller-scale, higher-latitude jets flowing in alternating directions. Jupiter's large thermal emission suggests that the winds are powered from within, but the zonal flow depth is limited by increasing density and electrical conductivity in the molecular hydrogen-helium atmosphere towards the centre of the planet. Two types of planetary flow models have been explored: shallow-layer models reproduce multiple high-latitude jets, but not the equatorial flow system, and deep convection models only reproduce an eastward equatorial jet with two flanking neighbours. Here we present a numerical model of three-dimensional rotating convection in a relatively thin spherical shell that generates both types of jets. The simulated flow is turbulent and quasi-two-dimensional and, as observed for the jovian jets, simulated jet widths follow Rhines' scaling theory. Our findings imply that Jupiter's latitudinal transition in jet width corresponds to a separation between the bottom-bounded flow structures in higher latitudes and the deep equatorial flows.

Experimental study and sterilizing application of atmospheric pressure plasmas

The atmospheric pressure surface barrier discharge (APSBD) in air has been used in killing Escherichia coli. We have developed two similar dielectric barrier discharge (DBD) structure types of nonthermal plasma jets (PJ) driven by 5–20 kHz audio-frequency power at atmospheric pressure. At a flow rate of 200 L/h (argon), a stable, arc-free discharge was produced. At 1.5 cm from the nozzle, the gas temperature was kept at 47 °C for PJ-1 source and 38 °C for PJ-2 source. Some research on sterilization has been carried out and results show that such a plasma jet source as PJ-2 is very effective in the disruption of E. coli.

The Infrared‐dominated Jet of 3C 401

We present a Hubble Space Telescope image of the FR II radio galaxy 3C 401, obtained at 1.6 μm with NICMOS, in which we identify the infrared counterpart of the brightest region of the radio jet. The jet has a complex radio structure and brightens where bending occurs, most likely as a result of relativistic beaming. We analyze archival data in the radio, optical, and X-ray bands, and we derive its spectral energy distribution. Unlike all of the previously known optical extragalactic jets, the jet in 3C 401 is not detected in the X-rays, even in a long 48 ks X-ray Chandra exposure, and the infrared emission dominates the overall spectral energy distribution (SED). We propose that the dominant radiation mechanism of this jet is synchrotron. The low X-ray emission is then caused by two different effects: (1) the lack of any strong external photon field and (2) the shape of the electron distribution. This affects the location of the synchrotron peak in the SED, resulting in a sharp cutoff at energies lower than the X-rays. Thus 3C 401 shows a new type of jet, with intermediate spectral properties between those of FR I galaxies, which are dominated by synchrotron emission up to X-ray energies, and FR II galaxies/QSOs, which show strong high-energy emission due to inverse Compton scattering of external photons. This might indicate the presence of a continuous in the properties of large-scale jets, analogous to the blazar sequence already proposed for subparsec-scale jets.

Separation and Transition Control on an Aft-Loaded Ultra-High-Lift LP Turbine Blade at Low Reynolds Numbers: Low-Speed Investigation

An experimental study was conducted to improve the performance of an aft-loaded ultra-high-lift low-pressure turbine blade known as U2 at low Reynolds numbers. This was achieved by manipulation of the laminar-turbulent transition process on the suction surface. The U2 profile was designed to meet the targets of reduced cost, weight and fuel burn of aircraft engines. The studies were conducted on both low-speed and high-speed experimental facilities under the unsteady flow conditions with upstream passing wakes. The current paper presents the low-speed investigation results. On the smooth suction surface, the incoming wakes are not strong enough to suppress the separation bubble due to the strong adverse pressure gradient on the suction surface and the low wake passing frequency, which allows the separation between the wakes more time to re-establish. Therefore, the profile losses of this ultra-high-lift blade are not as low as conventional or high-lift blades at low Reynolds numbers even in unsteady flows. Two different types of passive separation control devices, i.e., surface trips and air jets, were investigated to further improve the blade performance. The measurement results show that the profile losses can be further reduced to the levels similar to those of the high-lift and conventional blades due to the aft-loaded nature of this ultra-high-lift blade. Detailed surveys of the blade surface boundary layer developments showed that the loss reduction was due to the suppression of the separation underneath the wakes, the effect of the strengthened calmed region and the smaller separation bubble between wakes.

Magnetohydrodynamic Simulation of Solar Coronal Chromospheric Evaporation Jets Caused by Magnetic Reconnection Associated with Magnetic Flux Emergence

We studied solar coronal X-ray jets by MHD numerical simulations with heat conduction effects based on a magnetic reconnection model. Key physical processes are included, such as the emergence of magnetic flux from the convection zone, magnetic reconnection with the coronal magnetic fields, heat conduction to the chromosphere, and chromospheric evaporation. Radiation, however, has been neglected. High-density evaporation jets were successfully reproduced in the simulations. The mass of the evaporation jets M is described as M = 6.8 × 1012g(B/10 G)15/7(Tcor/106 K)5/14(L/5000 km)12/7(t/400 s), where B is the strength of magnetic fields, Tcor is the coronal temperature, L is the loop height, and t is the duration of ejection, respectively. We also derived a theoretical model of the Mach number of the reconnection jets as a function of ambient coronal variables. Numerical simulations also show that two different types of jets (evaporation jets and low-density jets) exist simultaneously around the emerging flux region, and the energy of evaporation jets is somewhat larger than that of the low-density jets.

Study on an Atmospheric Pressure Plasma Jet and its Application in Etching Photo-Resistant Materials

An atmospheric pressure radio-frequency plasma jet that can eject cold plasma has been developed. In this paper, the configuration of this type of plasma jet is illustrated and its discharge characteristics curves are studied with a current and a voltage probe. A thermal couple is used to measure the temperature distribution along the axis of the jet stream. The temperature distribution curve is generated for the He/O2 jet stream at the discharge power of 150 W. This jet can etch the photo-resistant material at an average rate of 100 nm/min on the surface of silicon wafers at a right angle.

Aluminum Surface Treatment Using Three Different Plasma-Assisted Dry Chemical Processes

Aluminum plate surfaces having hydrophilic and corrosion-resistant properties are often required for various mechanical parts or systems. The conventional process for treating aluminum surfaces employs a series of wet processes: grease or organic compounds removal followed by drying, chromate process followed by drying, and finally chemical treatment to achieve hydrophilic property. However, the use of chromium (Cr/sup +6/) in the chromate process creates an environmental problem. A simple and economic dry process was investigated to replace the conventional aluminum surface treatment, i.e., nonthermal plasma followed by the chemical process. Among several nonthermal plasma processes, two types of plasma jets (60-Hz ac plasma and RF plasma) and the pulsed-corona plasma were investigated. The adhesive characteristics between the aluminum surface and the corrosion-resistant chemical were evaluated by the accelerated corrosion test, i.e., copper-accelerated acetic acid spray (CASS) test. RF plasma with more than 30 s of exposure time followed by the epoxy-type corrosion-resistant coating showed a superior performance over the conventional chromate wet process. Pulsed corona process was nearly equal to the conventional process. Therefore, the conventional wet chemical process for aluminum treatment can be replaced by the newly developed plasma-assisted chemical process.

The polarization of afterglow emission reveals γ-ray bursts jet structure

We numerically compute light and polarization curves of γ -ray burst (GRB) afterglows for various configurations of the jet luminosity structure and for different dynamical evolutions. We especially consider the standard homogeneous ‘top hat’ jet and the ‘universal structured jet’ with power-law wings. We also investigate a possible, more physical variation of the ‘top hat’ model: the ‘Gaussian jet’. The polarization curves for the last two jet types are shown here for the first time together with the computation of X-ray and radio polarized fluxes. We show that the light curves of the total flux from these configurations are very similar to each other, and therefore only very high quality data could allow us to pin down the underlying jet structure. We demonstrate instead that polarization curves are a powerful means to solve the jet structure, since the predicted behaviour of polarization and its position angle at times around the jet break are very different, if not opposite. We conclude that the afterglow polarization measurements provide clear footprints of any outflow energy distribution (unlike the light curves of the total flux) and the joint analysis of the total and polarized flux should reveal the jet structure of GRBs.

Cross-Talk Reduction by Smart Delay Firing

As ink jet arrays become larger, the cross-talk between closely spaced firing channels becomes more severe resulting in an adverse impact on print quality. A method of addressing this problem applicable to any type of DOD ink jet without making any physical changes to the individual jet design and with only minimal changes to the array configuration is described.The individual channels of the array are divided into N interspersed groups and the permitted firing time of each group has its own small time delay, δ. An optimum delay is calculated for each group so that, when all channels are fired, there is a maximum amount of cross-talk cancellation. Because the firing channels are the source of an acoustic wave train predominantly at a resonant frequency of the channel, the interaction with other firing channels depends strongly on the phase relationship with the arriving wave. For any given print-head, a number of basic experimental measurements are made and the data used as input to a computer model, which calculates the change in drop velocity as a function of the delays for a channel near the centre of the array when all channels are firing. The basic equations and an outline of the computation are shown.

Hemolysis after mitral valve repair: mechanisms and treatment

Background The objectives of this study were to determine the mechanisms of hemolysis after mitral valve repair and to determine outcomes after surgical treatment (mitral replacement or re-repair). Methods Between 1981 and 2002, 32 patients (mean age, 58 years) presented with hemolytic anemia after mitral valve repair for degenerative, rheumatic, or ischemic mitral regurgitation (MR). Three types of annuloplasty were used at the initial mitral valve repair: Cosgrove-Edwards, Carpentier-Edwards, and bovine pericardial (Perigard). The diagnosis and the mechanisms of hemolysis were investigated with laboratory testing and echocardiography. Results Median interval from initial mitral valve surgery to diagnosis of hemolysis was 3 months (range, 1 week to 4 years). At presentation, mean hematocrit was 27.5% ± 4.9% and 22 patients (69%) required transfusion. Echocardiographic findings varied. Twenty-four patients (77%) had grade 3 or 4 MR. Mitral regurgitant jet types included fragmentation (11 patients, 34%), acceleration (10, 31%), slow deceleration (5, 16%), collision (4, 13%), and free jet (2, 6%). Mitral valve replacement was performed in 28 patients, mitral valve re-repair in 3, and 1 patient did not undergo reoperation. At reoperation the mitral valve repair was physically intact in 25 of 31 patients (81%). There were 2 hospital deaths in patients having reoperation (6%). Actuarial survival was 95% at 1 year and 85% at 5 years. In 1 patient recurrent mechanical hemolysis developed caused by a perivalvular leak after mitral valve replacement. Conclusions Hemolysis is a mode of failure of mitral valve repair. Patients with hemolysis generally present within 3 months of mitral valve repair. Although echocardiographic features varied, most patients had high-grade MR and regurgitant jets that fragmented or accelerated. Mitral valve replacement yields favorable outcomes for patients with hemolysis after mitral valve repair.

What Types of Jets Does Nature Make? A New Population of Radio Quasars

We use statistical results from a large sample of about 500 blazars, based on two surveys, the Deep X-Ray Radio Blazar Survey (DXRBS), nearly complete, and the ROSAT All-Sky Survey-Green Bank Survey (RGB), to provide new constraints on the spectral energy distribution of blazars, particularly flat-spectrum radio quasars (FSRQs). This reassessment is prompted by the discovery of a population of FSRQs with spectral energy distribution similar to that of high-energy-peaked BL Lac objects. The fraction of these sources is sample dependent, being ~10% in DXRBS and ~30% in RGB (and reaching ~80% for the Einstein Medium Sensitivity Survey). We show that these "X-ray-strong" radio quasars, which had gone undetected or unnoticed in previous surveys, indeed are the strong-lined counterparts of high-energy-peaked BL Lac objects and have synchrotron peak frequencies, νpeak, much higher than "classical" FSRQs, typically in the UV band for DXRBS. Some of these objects may be 100 GeV to TeV emitters, as are several known BL Lac objects with similar broadband spectra. Our large, deep, and homogeneous DXRBS sample does not show anticorrelations between νpeak and radio, broad-line region, or jet power, as expected in the so-called blazar sequence scenario. However, the fact that FSRQs do not reach X-ray-to-radio flux ratios and νpeak values as extreme as BL Lac objects and the elusiveness of high-νpeak high-power blazars suggest that there might be an intrinsic, physical limit to the synchrotron peak frequency that can be reached by strong-lined, powerful blazars. Our findings have important implications for the study of jet formation and physics and its relationship to other properties of active galactic nuclei.

Simulation of Laminar Slot Jets Impinging on a Moving Surface

Laminar flow and heat transfer on a moving surface due to a bank of impinging slot jets have been numerically investigated. Two types of jet, namely axial and knife-jet with an exit angle of 60 deg were considered. The surface velocity up to two times the jet velocity at the nozzle exit was imposed on the impinging surface. It has been observed that while with increasing velocity of the impinging surface, the total heat transfer reduces; the distribution pattern becomes more uniform. For the same amount of mass and momentum flux at the nozzle exit, heat transfer from the axial jet is considerably higher than that from the vectored jets at all surface velocities considered. It was found that the local heat transfer over the surface for the case of the axial jet and the knife-jet scales with Re0.5 and Re0.55, respectively.

MEMS-based piezoelectric array microjet

As an important non-invasive drug delivery method, aerosol therapy has become an attractive focus in the fields of both pharmacy and medical instruments and will be widely used in the future. Atomizing drug delivery system can be classified into jet nebulizer, ultrasonic ejector, and MEMS-based microjet. According to different driving ways, MEMS-based microjet mainly adopts resistance-heated, electrostatic, ultrasonic, and piezoelectric mechanisms. In this paper, a new type of piezoelectric micro-array jet for medical use is presented. The device consists of a fluid chamber, which is formed by a piezoelectric transducer bonded to a silicon wafer with nozzles. Inside the fluid chamber a continuous pressure wave generated by the piezoelectric transducer propagates towards the nozzles and squeezes the liquid out. The pressure generated by piezoelectric disk is theoretically analyzed. The vibration mode at the first order resonant frequency of the piezoelectric transducer is analyzed and tested. The fabrication and bonding techniques of silicon wafer are discussed. The droplet diameter and velocity that are important parameters of the microjet are tested. As a result, the droplets have a narrow diameter distribution and velocity distribution.

Molecules, muscles, and machines: universal performance characteristics of motors.

Animal- and human-made motors vary widely in size and shape, are constructed of vastly different materials, use different mechanisms, and produce an enormous range of mass-specific power. Despite these differences, there is remarkable consistency in the maximum net force produced by broad classes of animal- and human-made motors. Motors that use force production to accomplish steady translational motion of a load (myosin, kinesin, dynein, and RNA polymerase molecules, muscle cells, whole muscles, winches, linear actuators, and rockets) have maximal force outputs that scale as the two-thirds power of mass, i.e., with cross-sectional area. Motors that use cyclical motion to generate force and are more subject to multiaxial stress and vibration have maximal force outputs that scale as a single isometric function of motor mass with mass-specific net force output averaging 57 N x kg(-1) (SD = 14). Examples of this class of motors includes flying birds, bats, and insects, swimming fish, various taxa of running animals, piston engines, electric motors, and all types of jets. Dependence of force production and stress resistance on cross-sectional area is well known, but the isometric scaling and common upper limit of mass-specific force production by cyclical motion motors has not been recognized previously and is not explained by an existing body of theory. Remarkably, this finding indicates that most of the motors used by humans and animals for transportation have a common upper limit of mass-specific net force output that is independent of materials and mechanisms.