Ideal Jet Research Articles

Modeling of a Jet Pipe Servovalve Considering Nonlinear Flow Forces Acting on the Spool

The design and analysis of jet pipe servovalves are mostly based on linear models. However, there are some nonlinear factors in this kind of electromechanical–hydraulic structure. The article deduces a linear rotation equation for the armature assembly and a linear flow equation for the control cavity. With the consideration of nonlinear hydraulic reaction forces in the second stage, the nonlinear dynamic equation of the main spool in an ideal jet pipe servovalve is derived. Based on the MATLAB (R2016a) software, the nonlinear model of a certain type of jet pipe servovalve is numerically investigated. The equilibrium points of the nonlinear system are calculated, the phase portraits are plotted, and the Hopf bifurcations caused by the flow-pressure coefficient as the control parameter and the period-doubling bifurcations caused by the variation of the input signal are analyzed. The vibration frequency of the time-domain response of the fifth-order system with a cosine signal as input is 242 Hz, which is similar to the experimental value of 233 Hz. The relative error between the two is 3.9%, verifying the validity of the nonlinear system model.

Optimal conditions and generation mechanism of jet atomization for uniform distribution of nano- and micro-droplets

This study provides a jet atomization technique to uniformly distribute nano- and micro-particles on the substrate by enclosing them in water droplets to avoid their aggregation. Jet atomization is a two-dimensional uniform spray and is generated using a diaphragm. The ideal jet atomization was achieved when the diaphragm was highly hydrophilic (contact angle 9.8°), and the spring constant was approximately 1.27 N m−1. The several experiments in this study supported the idea that jet atomization was caused by surface wave formed on the water film, rather than by boiling or cavitation of the water. The resonance between the diaphragm and the surface wave was investigated using a simple model. The results of this study can be expected to make fundamental contributions to pharmacy, medicine, and environmental science, where the uniform distribution of fine particles such as drugs, DNAs, and microplastics is required for the analyses of their properties.

Вызванные скорости вне струи идеального движителя

Object and purpose of research. The paper is devoted to the analysis of induced flow velocities outside the ideal propeller jet. The purpose is to widen capabilities of estimations. Materials and methods. Analysis of data on this issue has shown that complicated and quite labor-consuming methods are used for these purposes. It is attempted to devise a calculation scheme based on direct determination of induced velocities from discrete sinks simulating the ideal propeller. For this purpose an algorithm and software is developed for PC implementation. Testing of the computer program allowed us to define conditions ensuring the accuracy of calculations, it confirmed practically full agreement with the data obtained by other authors and possibility for widening the range of its application. Main results. Systematic calculations of induced velocities outside the ideal propeller jet were done allowing us to determine the flow velocity at any point of a wide area for engineering purposes. Conclusion. Longitudinal and radial component velocities induced by ideal propeller outside its jet were calculated based on directly assessed influence of the system of sinks distributed over the propeller disk on the ideal fluid flow. The algorithm for calculations was developed, the software was written and tested. Systematic calculations of induced velocities were done, which could be used for practical estimations.

Numerical study on self-propulsion of a waterjet propelled trimaran

The hydrodynamics of the waterjet propelled ships represents a challenging problem due to the complexity of the waterjet system itself and the waterjet/hull interaction. In this paper, the self-propulsion computations of a trimaran were performed by solving the unsteady RANS equations. The waterjet was simulated directly with multi-reference frame model to improve the precision of the numerical simulations. Mesh independence studies of the hull and waterjet were carried out individually. Numerical simulations with/without the waterjet were performed in a speed range of 0.196 < Fr < 0.707. Comparisons between numerical predictions and experimental data showed the numerical method could accurately predict the self-propulsion performance. A numerical tool was developed to obtain the capture area based on tracking the streamlines upstream, which was practical and greatly simplified the post-processing. According to the ITTC procedures and guidelines, the overall efficiency and its components were analyzed in detail. The results showed that the resistance increment was always positive while the waterjet thrust deduction fraction was negative. The overall efficiency of the waterjet was mainly affected by the ideal jet efficiency and the pump efficiency. The analysis of the waterjet powering characteristics can better understand the energy conversion and the interaction between the ship hull and waterjet.

Numerical investigation of the jet velocity profile and its influence on the Pelton turbine performance

Numerical investigation of the unsteady flow patterns around the bucket can be helpful to improve the Pelton turbine efficiency. In fact, by studying the loss mechanisms in the flow, one can optimize the bucket design. For this purpose, an accurate investigation of the water jet is also necessary as an inlet condition for the bucket flow. The water jet ejected from the nozzle is actually non-uniform, due to the upstream turbulence and secondary flow in the distributor, bending pipes, needle and supports. This non-uniformity causes a deviation of the water jet from the ideal jet center, which is tangent to the jet circle, and it directly affects the flow patterns around the bucket. Whereas water splashing makes experimental observations very challenging, a numerical approach is effective and convenient to study the unsteady flow pattern in a Pelton turbine. In the present research, numerical analysis of the two-phase flow through the distributor, bending pipe and nozzle, has been performed. The jet velocity profile has been verified with experimental results, which are measured in the model test equipment, and good agreement is obtained for both velocity profile and jet deviation. In addition, the analysis of the bucket unsteady flow is performed using the aforementioned non-uniform jet velocity profile and the calculated flow pattern around the bucket is compared to the previous calculation using a uniform velocity profile at the inlet boundary. The difference between the two cases is discussed based on the quantitative and qualitative evaluation from the numerical analysis.

Inclusive production of plus a recoil for the LHC Run-II

This letter presents a study of the inclusive production of plus a recoil, using simulated samples of pp collisions at for an integrated luminosity in the range between and . The case for experiments to include un-prescaled b-tag multijet triggers for this topology is made and the ideal jet thresholds are discussed. The sensitivity to the Standard Model Higgs boson with a transverse momentum of at least 200 GeV is evaluated with respect to a continuous background, dominated by multijet processes. The mass of b-jet-pairs is analysed, quoting sensitivity to cross-sections in the range from 1 to 2 pb, for , covering the total Higgs-boson production cross-section of 1.8 pb. The trigger strategy presented in this letter is compared to triggers already in use, showing an increase on the signal efficiency for masses below 200 GeV and a performance comparable to a logical OR of all the currently available akin triggers for higher masses. The robustness of the expected sensitivity against systematic uncertainties is estimated by considering various typical sources, such as those on the fitting parameters of the continuous background, shape uncertainties affecting the signal acceptance and the background modelling. The accuracy of the Higgs-boson production cross-section measurements is also discussed, quoting sensitivity to deviations of 50% for and 10% for .

Research into the process of impingement of two plane jets of an ideal fluid with free boundaries

The problem of finding parameters stationary jets, outgoing from a place of impact of two incoming flat ideal jets with free boundaries and possessing the identical speed, but various width, has no decision. Various models are widely used for a conclusion of the missing equation now, but they lead to contradictory results. The new model is offered. Adequacy to the offered model was checked by comparison results with data of the numerical calculations in ANSYS AUTODYN. The dependence approximating results of numerical calculations is developed to increase accuracy in calculations of angular provision of the internal outgoing jet.First of all, the executed researches are interesting to experts, who works on behavior low- value technological errors in shaped charges.

Heat transfer of Single Impinging Jet with Cu Nanofluids

In this study, the comprehensive performance of a heat exchanger with an impinging jet cooling system was experimentally investigated through nanofluids. Furthermore, heat transfer efficiency was mainly determined by comparing different flow rates, jet heights, and types of nanofluids. Results show that the use of nanofluids on impinging jet cooling systems significantly improved heat transfer efficiency and that the pressure drop in the system did not change considerably. Unlike different jet conditions, nozzle shape affected the heat transfer coefficient significantly. When nanofluids are employed as the working fluid, the convective heat transfer coefficient was higher in circular nozzles than in square nozzles. Moreover, the larger the jet angle, the stronger the heat transfer effect; the ideal jet impingement cooling effect is achieved when the jet angle reaches 90°. In addition, a particular nozzle size maximizes the heat transfer effect at the same jet conditions.

Jet quality characteristics according to nozzle shape of energy-recovery Pelton turbines in pressure-retarded osmosis

AbstractPelton turbines are used for energy recovery in pressure-retarded osmosis (PRO) systems. The quality of jet sprays is a significant factor affecting the performance of these turbines. This study examined jet quality characteristics according to the nozzle geometry of Pelton turbines. Jet quality tests were conducted to analyze the degree of similarity between the actual jet flow and the ideal jet flow. Power loss, discharge coefficients, and performance characteristics of Pelton turbines were examined with respect to the nozzle shape through performance tests of the nozzles and turbines. Furthermore, jet flows were numerically analyzed. The test results and analyses confirm that for a given input power, the recirculation region increases and the jet quality decreases with increasing nozzle throat angle. On the basis of the results, the optimum range of nozzle throat angle for Pelton turbines in PRO systems is suggested.

An approximate model of the dynamics and heat transfer of an impact cylindrical ideal liquid jet

A jet model based on approximations of velocities, satisfying the continuity equation, and on the integral momentum equation is presented. The solution for the jet dynamics turned out to be nonmonotonic: as an obstacle recedes over a distance larger than a certain critical one, the jet escapes from the receiver nozzle rectilinearly and remains unchanged until the distance to the obstacle becomes equal to the critical one, whereupon the jet begins to spread. The heat transfer law has been determined on the basis of the momentum and boundary layer energy equations written in an integral form. They were solved by the Squire method. It is shown that with decrease in the distance to the obstacle, if it is smaller than the critical one, the Nusselt number at the stagnation point increases.

A NUMERICAL STUDY OF FLUID INJECTION AND MIXING UNDER NEAR-CRITICAL CONDITIONS

Nitrogen injection under conditions in close vicinity of liquid-gas critical point is studied through numerical simulation. The thermodynamic and transport properties of fluid exhibit anomalies in the near-critical fluid regime. These anomalies can cause distinctive effects on heat transfer and hydrodynamics. To focus on the influence of the highly variable properties and avoid the difficulties encountered in modeling high Reynolds number flows, a relatively low injection Reynolds number is adopted. A reference case with the same configuration and Reynolds number is also simulated in the ideal gas regime. Full conservation laws, real-fluid thermodynamic and transport phenomena are accommodated in the model. The obtained results reveal that the flow features of the near-critical fluid jet are significantly different from the ideal gas case. The near-critical fluid jet spreads faster and mixes better with the ambient fluid compared to the ideal gas jet. It is also identified that vortex pairing process develops faster in the near-critical case than in the ideal gas case. Detailed analysis of data at different streamwise positions including both flat shear layer region and fully developed vortex region reveals the effect of volume dilatation and baroclinic torque plays an important role in the near-critical fluid case. The volume dilatation effect disturbs the shear layer and makes it more unstable. The volume dilatation and baroclinic effects strengthen the vorticity and stimulate the vortex rolling up and pairing process.

Simple thermodynamics of jet engines

We use the first and second laws of thermodynamics to analyze the behavior of an ideal jet engine. Simple analytical expressions for the thermal efficiency, the overall efficiency, and the reduced thrust are derived. We show that the thermal efficiency depends only on the compression ratio r and on the velocity of the aircraft. The other two performance measures depend also on the ratio of the temperature at the turbine to the inlet temperature in the engine, T3/Ti. An analysis of these expressions shows that it is not possible to choose an optimal set of values of r and T3/Ti that maximize both the overall efficiency and thrust. We study how irreversibilities in the compressor and the turbine decrease the overall efficiency of jet engines and show that this effect is more pronounced for smaller T3/Ti.

Development of a Downhole Separator and Intensifier for Coiled Tubing Jetting

Abstract Wells often build scale deposits on the inside of their tubulars that can impede production or interfere with a workover operation. When this scale buildup is over long intervals, coiled tubing (CT) is often the conveyance system used to deliver acid, drilling or jetting technologies to remove the scale. Acidizing through coil can be effective only if the scale is acid soluble and it can be expensive. Drilling with motors can be very effective, but motors are susceptible to performance issues, especially if high nitrogen ratios are required. Jetting the scale is possible, but this technology also faces challenges. Delivering sufficient downhole hydraulic pressure to overcome the scale's threshold pressure is very difficult due to the limited pressure capacity of CT and frictional pressure losses in long CT strings. Further, if nitrogen is required to ensure returns, the gas phase quickly disperses the fluid jet as it exits the jetting tool, and very little power is delivered to the scale face. Recent technical advances in CT jetting technology include a rotary separator to separate the nitrogen from the fluid and a downhole pressure intensifier to take the separated water and increase the hydraulic pressure delivered to the jetting tool. The paper first discusses measurements of the threshold pressure required for removal of oilfield scales. The development of a gas separator and downhole intensifier are discussed next, followed by the results of testing these tools. Introduction Mineral scale deposits inside of production tubing can reduce production or interfere with workover operations. Coiled tubing is used to remove this scale using motors or jetting tools. Jet milling of scale is an attractive option because fluid jets will not damage tubulars or other downhole equipment. Jet milling capabilities are limited by the threshold pressure required to initiate milling and by fluid jet dissipation. The jet pressure delivered to the scale surface determines the ability of the jet to cut a given scale. The jet power then determines the rate at which the scale can be removed. The pressure that can be delivered to a jetting tool through CT is limited by fatigue limits of the coil and the pressure capabilities of available pumps. The jet power, which determines milling rates, is further limited by friction pressure loss in the CT. These losses become more significant in deep wells. One approach to cutting scale at the pressure available using coil is to add abrasives(1), however, this approach adds cost and complexity to the operation. Another approach is to boost the pressure of the jets with a downhole intensifier. In the 1990s, the FlowDril Corporation manufactured a large-scale downhole intensifier pump to drill 77/8 in to 83/4 in holes with jet assisted roller cone bits(2). The unit was designed to work with a conventional rotary drill string and run on drilling mud. The intensifier ratio was 14:1, delivering 84 l/min at 200 MPa from mud supplied at 1,260 l/min and 23 MPa. A similar approach would allow CT pressure to be boosted to a level capable of milling hard scale. The effectiveness of fluid jetting tools is further limited by dissipation of the jet in the high pressure well environment. Submerged, non-cavitating fluid jets are subject to rapid dissipation due to turbulent mixing of the fluid. The maximum length of the high pressure jet core produced by an ideal jet under these conditions is under seven nozzle diameters(3). Intense turbulence persists to a range of around 20 nozzle diameters. By contrast, water jets in air can be effective at ranges of over 1,000 nozzle diameters. Jet dissipation effects

Optimal Static Characteristics of Amphibious PAR Vehicles

Power augmented ram platform vehicle is a high-performance air-assisted amphibious transport of the new generation. The objective of this study is to determine the optimal position of the platform flap for low-speed operations on water and solid ground. The static friction of vehicle hulls on solid surfaces and the static deformation of the water surface are combined with results of the ideal jet theory to predict forces and the platform position. The optimal values for the flap gap are obtained that maximize the recovered static thrust on solid surfaces and the vehicle vertical position on the water surface.

Research on One Borehole Hydraulic Coal Mining System

The Borehole Hydraulic Coal Mining System (BHCMS) causes fragmentation of coal seams and removes coal slump through a drilled hole using high-pressure water jet. Then the mixture of coal and water as slurry are driven out of the borehole by hydraulic or air-lifting method, and are separated at the surface. This paper presents a case study of hydraulic borehole coal mining. The three key techniques of the BHCMS, namely, hydraulic lift of jet pump, air lift, and water jet disintegration are discussed and analyzed in this paper based on theoretical analysis and field experiments. Some useful findings have been obtained: (1) The design of jet pump, air lift system, and water jet has to be integrated appropriately in order to improve mining efficiency and coal recovery rate, and to decrease energy consumption. The design of hydraulic lift jet pump must meet the requirement of the minimum floating speed of coal particles. The optimization of nondimensional parameters and prevention of cavitation have to be considered in the design; (2) With regard to selecting the nozzle types of jet pump, center nozzle or annular nozzle can be selected according to the size of the removed particles; (3) Through air-lift and back pressure, the water head can be decreased to improve the lift capacity of jet pump and decrease the power loss. The air lift has great limitation if it is used solely to extract coal, but if it is employed in conjunction with jet pump, the lift capacity of jet pump can be increased greatly; (4) With water jets, the air lift can improve the fragmentation radius and capacity. The main factors that affect the effect of water jet are the submergible status of jet, jet pressure, and flowrate. The ideal jet of the monitor in the borehole hydraulic coal-mining system is a nonsubmergible free jet. Through air lift, the nonsubmergible free jet can be set up in the mining hole.

Design and Penetration Performance of Annular Shaped Charge Structure

Based on the principle of the equivalent momentum of the corresponding elements for internal and external liners, annular shaped charge structure is proposed. The generatrix analytical equations for the external surfaces of the external liner and external charge are deduced. Experimental and numerical studies are conducted to investigate the formation and penetration process of the jet for the annular shaped charge under different initiation radiuses, and the initiation radius corresponding to the detonation wave front matched with the liner is optimized. At this radius, shaped charge can form an ideal cylindrical jet. Moreover, the diameter of the jet approximates the theoretical diameter of the jet, and has satisfactory symmetry and focus.

Theory of an Ideal Jet Thrust Augmentor

A theory of the ideal jet thrust augmentor is presented. The conditions of optimal outflow of the active (primary) and passive (secondary) jets from the device under consideration are obtained by solving the variational problem of maximum average thrust realization. The inlet values of the mass and total enthalpy fluxes for both flows, their entropies, and the inlet value of the passive-gas momentum component parallel to the flight velocity are preassigned. These conditions correspond to the use of jet engines, including a bypass turbojet gas generator, operating in steady mode, as well as a pulsed detonation rocket engine, as the high-pressure gas source. Along with the work done by the high-pressure gas on the low-pressure one, the gases may exchange heat. The possibility of heat transfer results in an appreciable increase in ideal thrust augmentor performance.

Self-Collimated Stationary Disk Winds

In this contribution, we first review the theory of self-collimated jets launched from magnetized accretion disks (disk-winds originating from the first AUs). We show why it is crucial to solve in a self-consistent way the interplay between the resistive accretion disk and the ideal MHD jets. Indeed, this is the only way to get exact values for the disk ejection efficiency ξ (the jet mass load issue). Then, we show self-similar calculations of such accretion-ejection structures: first cold jets, then warm jets obtained in the presence of a hot disk chromosphere. Finally, we present for the first time an accretion-ejection flow crossing all three critical points.

Magnetized Accretion‐Ejection Structures: 2.5‐dimensional Magnetohydrodynamic Simulations of Continuous Ideal Jet Launching from Resistive Accretion Disks

We present numerical magnetohydrodynamic (MHD) simulations of a magnetized accretion disk launching trans-Alfve·nic jets. These simulations, performed in a 2.5-dimensional time-dependent polytropic resistive MHD framework, model a resistive accretion disk threaded by an initial vertical magnetic ield. The resistivity is only important inside the disk and is prescribed as … mVAH exp﷿ 2Z 2 =H 2 fi, where VA stands for Alfve·n speed, H is the disk scale height, and the coecien t m is smaller than unity. By performing the simulations over several tens of dynamical disk timescales, we show that the launching of a collimated outiow occurs self-consistently and the ejection of matter is continuous and quasi-stationary. These are the irst eversimulationsofresistiveaccretion disks launchingnontransient ideal MHD jets. Roughly15% ofaccreted mass is persistently ejected. This outiow is safely characterized as a jet since the iow becomes superfast magnetosonic, well collimated, and reaches a quasi-stationary state. We present a complete illustration and explanation of the eeaccretion-ejectionee mechanism that leads to jet formation from a magnetized accretion disk. In particular, the magnetic torque inside the disk brakes the matter azimuthally and allows for accretion, while it is responsible for an eecti ve magnetocentrifugal acceleration in the jet. As such, the magnetic ield channels the disk angular momentum and powers the jet acceleration and collimation. The jet originates from the inner disk region where equipartition between thermal and magnetic forces is achieved. A hollow, superfast magnetosonicshellof densematerial isthenatural outcome of theinward advectionofaprimordial ield. Subject headings: accretion, accretion disks N galaxies:jets N ISM:jets and outiows N MHD

Nonlinearity caused by nonstationary perturbations of ideal jet flow past an obstacle

The problem is analyzed in the small perturbation theory approximation. It is shown that the dynamic boundary condition nonlinearity related to the presence of an inertial pressure force results in the flow velocity field becoming discontinuous and, as a consequence, in the appearance of infinite-sheeted spirals on free boundaries. The moment of onset of the discontinuity and its propagation law are found. It is shown that hydrodynamic forces can be calculated using formulas derived on the basis of a linear approximation.