Side Jet Research Articles

Large eddy simulation of the hydrodynamic behavior of horizontal side jets in compound open channels with vegetated floodplain.

Understanding the hydrodynamic behavior of side jets in compound open channels with vegetated floodplain is crucial to jet dilution, sediment transport, and bank stability. Large eddy simulation was used to study horizontal side jets in compound open channels with vegetated floodplain. Predicted mean velocity, turbulent kinetic energy, and secondary currents were compared with experimental data, with a good agreement between measured and calculated data. Analyses of bed shear stress showed that vegetation in the floodplain increases the total drag and decreases bed shear stress, thus governing sediment transport and protecting the bank. The transport mechanism was quantitatively investigated by the quadrant analysis, concentration, and Reynolds flux. The ejection and sweep events were major contributors to the momentum and scalar flux transport. Analyses of concentration and Reynolds flux showed that the secondary flow influenced the spreading of the jet and the location of the concentration peaks, and the distribution of concentration and Reynolds flux did not strictly follow Fickian law in the whole region due to the effect of secondary flow on the concentration distributions. Additionally, the typical vortexes and spatiotemporal evolution of vortex structures in compound open channels, especially those near the junction between the main channel and floodplain, were successfully demonstrated.

Influence of High-Voltage Electrode Arrangement on Downstream Uniformity of Jet Array

Atmospheric-pressure plasma jet (APPJ) array could effectively enlarge the treatment area for the requirement of application efficiency. The downstream uniformity of jet array is the determinant for the even processing effect. In this paper, a three-jet 1-D APPJ array with the electrode structure of needle–ring is constructed, and the position of needle electrode (high-voltage electrode) is adjusted to investigate the influence of electrode arrangement on the downstream uniformity of the 1-D APPJ array. The results show that the relative difference of the positions of the middle and side needle electrodes ${d}$ has great influence on the downstream uniformity. When the distances of the middle and side needle electrodes to the tube nozzles ${a}$ and ${b}$ are both fixed at 40 mm ( $d= 0$ mm), the middle plume is suppressed. With increasing the distance of the side needle electrodes to the tube nozzles ${b}$ to make $d=1$ , 2, and 3 mm, the middle plume is prolonged and the lengths of all plumes are almost equal at $d=2$ mm. With the intensified charge-coupled device (ICCD) image measurement, it is found that the desirable synchronicity of bullets propagation is obtained at $d = 2$ mm. The electrical field distributions of different d are simulated, which can be seen that the high electric fields of the side jets can suppress the propagation of middle jet and at $d= 2$ mm, the three jets have similar maximum values of the electrical field strength along the direction of needle electrode resulting in similar plume lengths in the APPJ array.

Neighboring optimal guidance and constrained attitude control applied to three-dimensional lunar ascent and orbit injection

Future human or robotic missions to the Moon will require efficient ascent path and accurate orbit injection maneuvers, because the dynamical conditions at injection affect the subsequent phases of spaceflight. This research is focused on the original combination of two techniques applied to lunar ascent modules, i.e. (i) the recently-introduced variable-time-domain neighboring optimal guidance (VTD-NOG), and (ii) a constrained proportional-derivative (CPD) attitude control algorithm. VTD-NOG belongs to the class of implicit guidance approaches, aimed at finding the corrective control actions capable of maintaining the spacecraft sufficiently close to the reference trajectory. CPD pursues the desired attitude using thrust vector control and side jet system, while constraining the rates of both the thrust deflection angle and the roll control torque. After determining the optimal two-dimensional ascent path, which represents the reference trajectory, VTD-NOG & CPD is applied in the presence of nonnominal flight conditions, namely those due to navigation and actuation errors, incorrect initial position, unpredictable oscillations of the propulsive thrust, and imperfect modeling of the spacecraft mass distribution and variation. These stochastic deviations are simulated in the context of extensive Monte Carlo campaigns, and yield three-dimensional perturbed trajectories. The numerical results obtained in this work unequivocally demonstrate that VTD-NOG & CPD represents an accurate and effective methodology for guidance and control of lunar ascent path and orbit injection.

The influence of pulse parameters on the downstream uniformity of linear-field jet array in argon

The nanosecond (ns) pulse excited plasma jet array shows merits of large treatment area and high chemical reactivity, while the pulse parameters influence the downstream uniformity of the ns pulse excited jet array significantly. In this paper, the downstream uniformity of the ns pulsed jet array with linear-field electrode structure is investigated by discharge image measurement at different amplitude of applied voltage, rising time and pulse repetition frequency (PRF). The voltage-current waveform and Schlieren image are measured and the electrical field distribution of the jet array is simulated to reveal the interaction mechanisms. The experimental results show that the divergence of side plumes becomes severer and the plume length of all three jet units becomes longer at higher applied voltage, which is caused by the enhancement of the electron energy and density. The shorter rising time also increases the transported charge and input energy and extends the length of the plasma plumes. At 0.5 L/min Ar flow rate, all of the lengths of plumes increase with PRF although the laminar regimes of the gas flows are reduced. At Ar flow rate of 1, 2, and 4 L/min, the middle jet is suppressed, which is analyzed by the electrical field distribution simulation. It is shown that the highest electric fields at the outside walls of side jet units, which suppress the propagation of ionization front from the orifice to the outer space of the middle jet. At lower Ar flow rate, there are severe depletion of electrons in the side jets by oxygen and penning ionization in the middle jet by background molecules, which result in the enhancement of the jet array downstream uniformity. The results are of importance to optimize pulse parameters for the realization of controllable and scalable pulse excited jet array for various applications.

Effect of Rocket Engine Layouts on Jet Flowfield Inside a Launch Pad

A numerical analysis is conducted to understand the flowfield inside a launch pad affected by the layouts of clustered rocket engines for the first stage. The Japanese H3 launch vehicle with typical rocket engines and a launch pad is selected for analysis. In a configuration having three clustered liquid-propellant rocket engines at a core stage, the exhaust jets from adjacent engines are found to interact with each other after impinging on the flame deflector, resulting in side jet reversal in the upstream direction along the flame deflector. An investigation of the layouts of solid rocket boosters around the core stage reveals that exhaust jets from the solid rocket boosters interfere with those from liquid-propellant rocket engines spreading on the flame deflector. This interference also causes reversed jets. Guidelines for suppressing such jet reversal are proposed for designing a launch vehicle and a launch pad for clustered rocket engines at the first stage.

Numerical simulation and optimization of hydrodynamics in a novel integral multi-jet spout-fluidized bed

The hydrodynamics in a novel integral multi-jet spout-fluidized bed was simulated using both Eulerian-Eulerian approach and the kinetic theory of granular flows. The effect of side jet number and side jet width on gas-solid two phase flow in the integral multi-jet spout-fluidized bed (IMJSFB) was investigated. The CFD results show that when the number of side jet is greater than 1 (N = 2–5), a wave-like spout and stable spout structure is formed in the IMJSFB. Compared with simulation results in the single nozzle spouted bed, the profiles of particles' velocity and concentration along the radial direction in the IMJSFB become relatively flatter. The integral uniformity of particle velocity distribution in spouted bed can be enhanced by increasing δ/Di. The particle flow factor (η) decreases first and then increases with the increase of δ/Di, and η reaches its minimum value when δ/Di = 0.208. On the whole, there is a set of optimal design parameters of side jet (N = 4, δ/Di = 0.208), at which, the fluidization quality particle phase in spout-fluidized bed reaches the optimum state while the bypass fluidizing air supply auxiliary equipment is omitted. The fluidization quality of particles in annulus can be significantly enhanced in the IMJSFB while the bypass fluidizing air supply auxiliary equipment is omitted.

Side-jet effects in high-pressure turbulent flows: Direct Numerical Simulation of nitrogen injected into carbon dioxide

Direct Numerical Simulation realizations were generated of a round jet under high-pressure (high-p) turbulent conditions. In the simulations, a jet of nitrogen was injected into a chamber filled with carbon dioxide for three different jet-to-chamber density ratio, s, and three different chamber pressures, pch,0. The results show that for s = 0.5 and 0.35 side jets form whereas no side jets are observed for s = 1; thus providing, for the first time, evidence of side jet formation in high-p flows. Due to these side jets, mixing of the jet fluid and chamber fluid is promoted; although the species experience regular diffusional mixing, it is shown that due to turbulent conditions there can be effective uphill thermal conduction. Analysis of the vortical features of the side jets elucidated the process through which the enhanced mixing occurs: fluid from the jet is effectively pumped in the radial direction though the combined action of dilatation/compression and vortex stretching/shrinking. The value of s is shown to control radial and circumferential mixing versus axial mixing which occurs through jet penetration in the flow. Examination of dynamic and thermodynamic quantities indicates that side jets also promote flow unsteadiness. The pressure in the chamber is demonstrated to have negligible effect on the side jets.

Experimental data for code validation: Horizontal air jets in a semicircular fluidized bed of Geldart Group D particles

Experiments were conducted with 6 mm plastic beads (Geldart Group D) in a semi‐circular, gas‐fluidized bed with side jets. Attention was paid to particle characterization and bed measurements, making the resulting dataset ideal for CFD‐DEM validation and uncertainty quantification. The bed was operated slightly above and below the minimum fluidization velocity, with additional fluidization provided by one of two pairs of opposing jets located above the distributor near the flat, front face of the unit. Care is taken to report material properties and bed conditions with either measured distribution functions or uncertainty bounds. High‐speed video imaging and particle tracking velocimetry are used to extract bin‐averaged velocity profiles, which are used to extract jet penetration depths. The time‐averaged mean and standard deviation of the bed pressure drop is also reported. Finally, the lower jets are also inserted into the bed until the opposing jets merge to form a spout‐like pattern. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2351–2363, 2018

Insights into process innovation through ultrasonically agitated concentric flow dielectric streams for dry wire electric discharge machining

ABSTRACT Application of gaseous dielectric in place of liquid dielectric for wire electric discharge machining (WEDM), popularly known as dry wire electric discharge machining (DWEDM), offers technological solutions to some environmental and metallurgical issues pertaining to process. However, conventional side jet stream of dielectric in dry WEDM renders ineffective debris removal from sparking gap to cause unwanted arcing. Moreover, side thrust on the wire surface tends to induce wire vibrations and results into uneven geometrical profiles. To harness full potential of DWEDM technology, it is imperative to improve cutting characteristics of process by minimizing the adverse impacts of side jet stream of dielectric. In this research work, the authors have conceptualized and demonstrated the idea of using concentric flow pattern of gaseous dielectric as a novel technological solution to limitations of DWEDM process by introducing ultrasonic-agitated concentric dry wire electric discharge machining (UCDWEDM). Experiments have been performed on Ti–6Al–4V material. Ultrasonically agitated pressurized air streams were supplied through indigenously developed concentric and side flow nozzles mounted on experimental set up. The experimental results showed that concentric flow mode of dielectric supply has outperformed the conventional side flow mode with 42% higher CV, 22% lower SR, and 8% lesser KW. Process mechanism of UCDWEDM is based on high velocity of air in concentric flow and ultrasonic-agitation in spark gap and suggested that UCDWEDM has potential to replace conventional dielectric supply system in DWEDM.

Spiky Structures around Reconnection Exhausts in the Solar Wind

Abstract The paper presents for the first time observations of unusual reconnection events in the solar wind. In all solar wind types, we identify magnetic reconnection exhausts accompanied by one or two side jets. This complex structure is created around a single current sheet and the jet(s) oriented in the same direction as the main exhaust is (are) spatially separated from it. A statistical analysis of reconnection exhausts in Wind observations (422 events) revealed that about 12% of exhausts is accompanied with one side jet and 3% of exhausts is bounded by two side jets, one on each side. Multispacecraft observations of events allow us to conclude that these structures are not consistent with a folding of the reconnection exhaust boundary. A source of these side jets is probably multiple or patchy reconnection at or close to the heliospheric current sheet. We suggest a scenario based on multiple reconnection that would lead to the presence of two side jets. A single jet is caused by a broken X-line consisting of two or more spatially separated parts.

Ignition of ultra-lean premixed H2/air using multiple hot turbulent jets generated by pre-chamber combustion

A detailed investigation on the ignition characteristics of ultra-lean premixed H2/air mixtures by multiple hot turbulent jets in a dual combustion chamber system was carried out. Simultaneous high-speed Schlieren and OH∗ chemiluminescence imaging were applied to visualize the jet penetration and ignition processes inside the main combustion chamber. The focus was on the effects of the spark location and fuel/air equivalence ratio within the pre-chamber on the ignition pattern of the main-chamber mixture. The results show that multiple jets resulted in similar lean flammability limit of H2/air as the single jets, given that the total nozzle areas are the same. However, the ignition probability improved significantly near the lean flammability limit using multi-jets compared to single jets. Additionally, depending on the spark location and pre-chamber equivalence ratio, either the side jet, the middle jet, or all the jets can initiate ignition in the main chamber. The ignition characteristics of straight and angled multi-jets were compared, and angled jets produced shorter main chamber burn time. Numerical modeling of the flame propagation process within the pre-chamber was carried out to explain the behavior of individual jets in a multi-jet system. It was found that depending on the pre-chamber spark position, the flame shape inside the pre-chamber changes drastically. The effective L/D ratio governs the flame dynamics in the pre-chamber and subsequently determines which jet (side, middle, or all) will first ignite the main chamber.

Effect of Fluid Viscosity on Noise of Bileaflet Prosthetic Heart Valve

Background. Numerical simulation and experimental research have been used as powerful tools to understand and predict the behavior and mechanics of the operation of natural heart valves and their prostheses in natural and patho­logical conditions. Such studies help to evaluate the effectiveness of the valves, their design and the results of surgical procedures, to diagnose healthy and impaired function of the heart valves. There is an actual problem in creating more reliable methods and tools for the operation diagnostics of mechanical heart valves.Objective. The aim of the research is to investigate the effect of fluid viscosity on the hydroacoustic characteristics of jets that flow from a semi-closed and open mechanical bileaflet heart valve. To study the possibility of using hydro­acoustic measuring instruments as diagnostic equipment for determining the working conditions of the bileaflet pro­sthe­tic heart valve.Methods. The experimental research was carried out by means of hydroacoustic measurements of the hydrodynamic noise in the near wake of the side and central jets of the glycerin solution and the pure water flow downstream of the prosthetic bileaflet heart valve.Results. The effect of fluid viscosity on the hydroacoustic characteristics of the jets that flow from a semi-closed and open mechanical bileaflet heart valve has been experimentally determined. Integral and spectral characteristics of the hydrodynamic noise of jets of the glycerin solution and the pure water flow downstream of the bileaflet mitral heart valve for different fluid rate were detected.Conclusions. In the stream conditions of pure water, the integral characteristics of the pressure field are lower than in stream conditions of the aqueous glycerin solution. As the glycerin concentration in the solution increases, increase average pressures and especially RMS pressure fluctuations. The spectral levels of the hydrodynamic noise in the near wake of the side jet of the glycerin solution are lower than for water flow in the frequency ranges from 1 to 7-8 Hz and from 100 to 1000 Hz for fluid rate 5 l/min. For higher fluid rates, the spectral components of the hydrodynamic noise in the near wake of the side jet of the glycerin solution of the semi-closed mitral valve are higher than that for the pure water. The greatest difference (1.5–1.8 times) in the spectral levels is observed in the frequency range from 10 to 100 Hz for the fluid rate 15 l/min.

Modeling and Assessment of Jet Interaction Database for Continuous-Type Side Jet

This paper describes the development and assessment process of a jet interaction aerodynamic database based on computational fluid dynamics data for a supersonic missile using a continuous-type side jet. The generation of the jet interaction aerodynamic database for the continuous-type side jet requires a large amount of simulation data, owing to the complex nature of jet interaction. To reduce the required number of simulations, seven jet-operating conditions were selected using geometrical symmetry at first; then, three-dimensional numerical simulations were conducted to build the jet interaction aerodynamic database in the reduced design space. Two modeling approaches were used in developing the jet interaction aerodynamic database. One was computational fluid dynamics based modeling with a full factorial sampling, and the other was surrogate modeling, based on the Latin hypercube sampling and Kriging method, for the interim database. The resulting two aerodynamic databases were assessed through comparison with flight test results. From the comparison, both models showed a suitable representation of the aerodynamic coefficients within 10% error during the jet operation period. This assessment confirmed that the jet interaction aerodynamic database for the missile with a continuous-type side-jet thruster can be constructed using numerical simulation data.

Effectiveness of a Reaction Control System Jet in a Supersonic Crossflow

A transverse side jet in a supersonic crossflow causes a significant region of separated flow in its vicinity. This separation alters the effectiveness of the jet in producing control forces and moments. In this study, numerical simulations are carried out in order to estimate this change in effectiveness. The effect of a number of parameters such as the angle of attack, angle of yaw, jet pressure ratio, injection Mach number, and presence or absence of a flare aft of the injection are studied. For the geometry considered, it is seen that the effectiveness is enhanced significantly as the angle of attack, angle of yaw, or the jet pressure ratio are increased. The jet injection Mach number does not have a significant effect as long as the jet pressure ratio and jet mass flow rate are unchanged.

Guidance and control laws design for a switched system with discontinuous actuators

SummaryGuidance and control laws design for a switched flight system with discontinuous actuators is dealt with in this paper. Firstly, a missile equipped with discontinuous side jets is introduced. Secondly, the side‐jet missile is modeled with an impulsive switched system. Thirdly, a sliding mode control‐based discontinuous guidance law is proposed to generate guidance commands, which are suitable for on–off side jets. And a logic‐based switching law for turning on the side jets is also submitted. Fourthly, by transforming the discontinuous actuators equivalently and formulating an extended state space equation, a tracking control law is indicated to track the guidance command. Finally, simulations and comparisons are made to demonstrate the proposed algorithms. Copyright © 2016 John Wiley & Sons, Ltd.

Impact of numerical method on a side jets formation in a round jet

Numerical analysis of a formation of side jets in an externally modulated round jet is presented. The research is performed applying Large Eddy Simulation method and high-order codes based on Cartesian and cylindrical coordinates. The main attention is paid to an impact of numerical approach on the formation of the side jets, their number and localisation. The results obtained suggest that on Cartesian meshes the number and directions of the side jets are dependent on the distribution of the mesh nodes.

Optimal perturbations in time-dependent variable-density Kelvin–Helmholtz billows

We analyse the influence of the specific features of time-dependent variable-density Kelvin–Helmholtz (VDKH) roll-ups on the development of three-dimensional secondary instabilities. Due to inertial (high Froude number) baroclinic sources of spanwise vorticity at high Atwood number (up to 0.5 here), temporally evolving mixing layers exhibit a layered structure associated with a strain field radically different from their homogeneous counterpart. We use a direct-adjoint non-modal linear approach to determine the fastest growing perturbations over a single period of the time-evolving two-dimensional base flow during a given time interval $[t_{0},T]$. When perturbations are seeded at the initial time of the primary KH mode growth, i.e. $t_{0}=0$, it is found that additional mechanisms of energy growth are onset around a bifurcation time $t_{b}$, a little before the saturation of the primary two-dimensional instability. The evolution of optimal perturbations is thus observed to develop in two distinct stages. Whatever the Atwood number, the first period $[t_{0},t_{b}]$ is characterised by a unique route for optimal energy growth resulting from a combination of the Orr and lift-up transient mechanisms. In the second period $[t_{b},T]$, the growing influence of mass inhomogeneities raises the energy gain over the whole range of spanwise wavenumbers. As the Atwood number increases, the short spanwise wavelength perturbations tend to benefit more from the onset of variable-density effects than large wavelength ones. The extra energy gain due to increasing Atwood numbers relies on contributions from spanwise baroclinic sources. The resulting vorticity field is structured into two elongated dipoles localised along the braid on either side of the saddle point. In return they yield two longitudinal velocity streaks of opposite sign which account for most of the energy growth. This transition towards three-dimensional motions is in marked contrast with the classic streamwise rib vortices, so far accepted as the paradigm for the transition of free shear flows, either homogeneous or not. It is argued that the emergence of these longitudinal velocity streaks is generic of the transition in variable-density shear flows. Among them, the light round jet is known to display striking side ejections as a result of the loss of axisymmetry. The present analysis helps to renew the question of the underlying flow structure behind side jets, otherwise based on radial induction between pairs of counter-rotating longitudinal vortices (Monkewitz & Pfizenmaier, Phys. Fluids A, vol. 3 (5), 1991, pp. 1356–1361). Instead, it is more likely that side ejections would result from the convergence of the longitudinal velocity streaks near the braid saddle point. When the injection time is delayed so as to suppress the initial stage of energy growth, a new class of perturbations arises at low wavenumber with energy gains far larger than those observed so far. They correspond to the two-dimensional Kelvin–Helmholtz secondary instability of the baroclinically enhanced vorticity braid discovered by Reinaud et al. (Phys. Fluids, vol. 12 (10), pp. 2489–2505), leading potentially to another route to turbulence through a two-dimensional fractal cascade.

A novel three-jet microreactor for localized metal-organic chemical vapour deposition of gallium arsenide: design and simulation

We present a novel three-jet microreactor design for localized deposition of gallium arsenide (GaAs) by low-pressure Metal-Organic Chemical Vapour Deposition (MOCVD) for semiconductor devices, microelectronics and solar cells. Our approach is advantageous compared to the standard lithography and etching technology, since it preserves the nanostructure of the deposited material, it is less time-consuming and less expensive. We designed two versions of reactor geometry with a 10-micron central microchannel for precursor supply and with two side jets of a dilutant to control the deposition area. To aid future experiments, we performed computational modeling of a simplified-geometry (twodimensional axisymmetric) microreactor, based on Navier-Stokes equations for a laminar flow of chemically reacting gas mixture of Ga(CH3)3-AsH3-H2. Simulation results show that we can achieve a high-rate deposition (over 0.3 μm/min) on a small area (less than 30 μm diameter). This technology can be used in material production for microelectronics, optoelectronics, photovoltaics, solar cells, etc.

NUMERICAL SIMULATION OF LATERAL CONTROL JETS OF AN INTERCEPTOR MISSILE

The interceptor missile is an anti-ballistic missile designed to counter the ballistic missiles like Intermediate Range Ballistic Missiles and Intercontinental Ballistic Missiles launched from any country. These missiles use side jets from their surface in order to target towards the ballistic missiles. The analysis of this side jet in the presence of free stream flow and its impact on the missile itself is of great importance. Since the jet comprises of chemically reactive species, it is essential to know the amount of attenuation of the radio signals passing through them. In the past few years many experiments and theoretical studies have been carried out to characterize the jet-atmosphere interaction in wind tunnel but it is difficult to scale these results to flight conditions because of free stream/plume chemistry, Reynolds number, surface, and wall interference effects. Therefore, it is necessary for computational studies to supplement the experimental efforts and explore the physics involved to obtain the performance characteristics and flow field structure of jet/atmospheric interaction. The objective of the present study is to simulate this lateral control jet and its effect due to presence of main free stream flow. The spherically blunted ogive shaped cylindrical body is used here as a typical shape representing the interceptor missile. The simulation is done using the CFD software package AnsysFluent (V15) at the given conditions of altitude 30 km and Mach 3, with and without jet & finally the results are compared.

Large Eddy Simulation Modeling of Non-Premixed Turbulent Oxy-Fuel Combustion Supplied by Three Separated Jets

ABSTRACTThe continuity of evolving pollutant emission regulations requires the design and the development of new burners. The separated-jets burner concept is an example that implies a careful understanding of the turbulent oxy-fuel flames properties developing in a furnace. Modeling, such as turbulent combustion, is a challenge, as it combines complex flow and transport phenomena with combustion events including a vast amount of species and reactions. The flamelet generated manifold (FGM) method is a promising technique to model reacting flows using a tabulated chemistry approach. It is considered as a function of the mixture fraction (Z) and a reaction progress variable (Y). In this work, the interaction of three aligned separated jets is numerically investigated. The central jet provides the natural gas and the others side jets provide the pure oxygen. Turbulence is modeled using the large eddy simulation model in which the dynamic Germano approach is applied to determinate the sub-grid scale stress. In the reacting case, the turbulence chemistry interaction is achieved by coupling the FGM tabulated chemistry within the computational fluid dynamic code. The numerical results show a good agreement with experimental data notably in the isothermal case. In the reacting case, statistical flow field quantities for velocity, mixture fraction, and temperature are analyzed in detail.