Steady Jet Research Articles

Fundamental Properties of Fluidic Oscillators for Flow Control Applications

The presented work provides a technical summary of the fundamental time-resolved properties of a spatially oscillating jet emitted by a fluidic oscillator. The discussion focuses on experiments involving a fluidic oscillator with two feedback channels. Although limited to the fundamental properties, the discussions throughout the paper are frequently directed at the use of fluidic oscillators for flow control applications, which is accompanied by numerous suggestions for future research activities. The internal flow field reveals the oscillation mechanism that is based on flow guided through the feedback channels to feed into a recirculation bubble. The bubble grows and pushes the jet to the opposite side. Scaling parameters are introduced that govern the oscillation frequency for different oscillator sizes and working fluids. The external flow field within a quiescent environment visualizes the jet’s sweeping motion. A head vortex is formed repetitively. The jet’s properties (e.g., jet velocity, jet depth, and entrainment) change throughout one oscillation cycle. The jet velocity decays much more rapidly than for a steady jet, which is accompanied by a significant increase in jet depth. These observations are consistent with the finding that the jet entrainment is at least four times higher than for a steady jet. Furthermore, the jet forces are assessed from the flow field data. When a single oscillating jet interacts with a crossflow over a flat plate, pockets of streamwise vorticity are formed and convected downstream. Depending on Strouhal number, the streamwise vortices alternate gradually or in an almost bi-modal manner.

OH planar laser-induced fluorescence measurements with high spatio-temporal resolution for the study of auto-ignition.

For the detailed understanding of transient combustion processes, in particular, of auto-ignition, quantitative measurements with high spatio-temporal resolution are desirable. These can, for instance, serve as validation data for time-resolved numerical simulations and in particular for the combustion models used in those simulations. In the current study, a jet-in-hot-coflow (JHC) burner, developed at the German Aerospace Center (DLR), the DLR JHC, was used to inject a turbulent methane jet into the hot exhaust gas of a lean hydrogen/air flame, and a steady state jet flame was established. In addition, fuel could be injected in a transient manner. Here, an auto-igniting jet was observed. The flame stabilization of the steady state jet flame and the auto-ignition during transient fuel injection were studied using high-speed laser-based and optical measurements. A strategy for quantifying high-speed OH planar laser-induced fluorescence is presented, and the measurement uncertainties are evaluated. The flame stabilization mechanism in steady state jet flames was assessed using probability density functions of the OH concentration at different axial and radial locations. The formation of auto-ignition kernels during transient fuel injection is evaluated based on time series of the OH concentration. It is shown how the OH concentration levels and PDF shapes can be used to characterize the chemical state of the reacting flow and to distinguish between auto-ignition and flame propagation.

The interaction between a spatially oscillating jet emitted by a fluidic oscillator and a cross-flow

This experimental study investigates the fundamental flow field of a spatially oscillating jet emitted by a fluidic oscillator into an attached cross-flow. Dominant flow structures, such as the jet trajectory and dynamics of streamwise vortices, are discussed in detail with the aim of understanding the interaction between the spatially oscillating jet and the cross-flow. The oscillating jet is ejected perpendicular to the cross-flow. A moveable stereoscopic particle image velocimetry (PIV) system is employed for the plane-by-plane acquisition of the flow field. The three-dimensional, time-resolved flow field is obtained by phase averaging the PIV results based on a pressure signal from inside the fluidic oscillator. The influence of velocity ratio and Strouhal number is assessed. Compared to a common steady wall-normal jet, the spatially oscillating jet penetrates to a lesser extent into the cross-flow’s wall-normal direction in favour of a considerable spanwise penetration. The flow field is dominated by streamwise-oriented vortices, which are convected downstream at the speed of the cross-flow. The vortex dynamics exhibits a strong dependence on the Strouhal number. For small Strouhal numbers, the spatially oscillating jet acts similar to a vortex-generating jet with a time-dependent deflection angle. Accordingly, it forms time-dependent streamwise vortices. For higher Strouhal numbers, the cross-flow is not able to follow the motion of the jet, which results in a quasi-steady wake that forms downstream of the jet. The results suggest that the flow field approaches a quasi-steady behaviour when further increasing the Strouhal number.

Numerical studies of active flow control on wing tip extension

PurposeIn the European project AFLoNext, active flow control (AFC) measures were adopted in the wing tip extension leading edge to suppress flow separation. It is expected that the designed wing tip extension may improve aerodynamic efficiency by about 2 per cent in terms of fuel consumption and emissions. As the leading edge of the wing tip is not protected with high-lift device, flow separation occurs earlier than over the inboard wing in the take-off/landing configuration. The aim of this study is the adoption of AFC to delay wing tip stall and to improve lift-to-drag ratio.Design/methodology/approachSeveral actuator locations and AFC strategies were tested with computational fluid dynamics. The first approach was “standard” one with physical modeling of the actuators, and the second one was focused on the volume forcing method. The actuators location and the forcing plane close to separation line of the reference configuration were chose to enhance the flow with steady and pulsed jet blowing. Dependence of the lift-to-drag benefit with respect to injected mass flow is investigated.FindingsThe mechanism of flow separation onset is identified as the interaction of slat-end and wing tip vortices. These vortices moving toward each other with increasing angle of attack (AoA) interact and cause the flow separation. AFC is applied to control the slat-end vortex and the inboard movement of the wing tip vortex to suppress their interaction. The separation onset has been postponed by about 2° of AoA; the value of ift-to-drag (L/D) was improved up to 22 per cent for the most beneficial cases.Practical implicationsThe AFC using the steady or pulsed blowing (PB) was proved to be an effective tool for delaying the flow separation. Although better values of L/D have been reached using steady blowing, it is also shown that PB case with a duty cycle of 0.5 needs only one half of the mass flow.Originality/valueTwo approaches of different levels of complexity are studied and compared. The first is based on physical modeling of actuator cavities, while the second relies on volume forcing method which does not require detailed actuator modeling. Both approaches give consistent results.

Experimental Investigation of Impinging Heat Transfer of the Pulsed Chevron Jet on a Semicylindrical Concave Plate

Impinging heat transferred by a pulsed jet induced by a six-chevron nozzle on a semicylindrical concave surface is investigated by varying jet Reynolds numbers (5000 ≤ Re ≤ 20,000), operational frequencies (0 Hz ≤ f ≤ 25 Hz), and dimensionless nozzle-to-surface distances (1 ≤ H/d ≤ 8) while fixing the duty cycle as DC = 0.5. The semicylindrical concave surface has a cylinder diameter-to-nozzle diameter ratio (D/d) of 10. The results show that the nozzle-to-surface distance has a significant impact on the impingement heat transfer of the pulsed chevron jet. An optimal nozzle-to-surface distance for achieving the maximum stagnation Nusselt number appears at H/d = 6. In the wall jet zone, the averaged Nusselt number is the largest at H/d = 2 and the smallest at H/d = 8. In comparison with the chevron steady jet impingement, the effect of nozzle-to-surface distance on the convective heat transfer becomes less notable for the pulsed chevron jet impingement. The stagnation Nusselt number under the pulsed chevron jet impingement is mostly less than that under the chevron steady jet impingement. However, at H/d = 8, the pulsed chevron jet is more effective than the steady jet. This study confirmed that the pulsed chevron jet produced higher azimuthally averaged Nusselt numbers than the steady chevron jet in the wall jet flow zone at large nozzle-to-surface distances. The stagnation Nusselt numbers by the pulsed chevron jet impingement have a maximum reduction of 21.0% (f = 20 Hz, H/d = 4, and Re = 2000) compared with that of the steady chevron jet impingement. Also, the pulsed chevron jet impingement heat transfer on a concave surface is less effective compared to a flat surface. The stagnation Nusselt numbers on the semicylindrical concave surface have a maximum reduction of about 37.7% (f = 20 Hz, H/d = 8, and Re = 5000) compared with that on the flat surface.

Characteristics of Steady and Unsteady Round Jets Induced by an Ultrasound Transducer

Characteristics of Steady and Unsteady Round Jets Induced by an Ultrasound Transducer

Structural Optimization of a Water Hydraulic Pilot-Operated Pressure-Reducing Valve

The characteristics of a pilot-operated pressure-reducing valve for water hydraulics are analysed. The valve operates well with a primary pressure of up to 15MPa, a secondary pressure range of 10MPa to 14MPa, and a flow range of 20L/min to 40L/min. Optimizations are applied to reduce the cavitation noise of the valve and to improve the pressure regulation accuracy of secondary pressure. The first optimization is executed by reducing pressure drop and velocity through the throttle of main spool and the second optimization is carried out by lowering down the steady jet force on both main spool and the pilot spool. The dynamic characteristics of the secondary pressure are obtained by simulations. The results show the valve behaviours better with the improvement structure. The average variation of the secondary pressure is brought down from 0.308MPa to 0.175MPa under different primary pressure conditions and from 0.288MPa to 0.136MPa under different inlet flowrate conditions. The velocity through throttle of the main spool is 31.18% cut down on average.

Incompressible Jet Flows in a de Laval Nozzle with Smooth Detachment

In this paper, we are concerned with the well-posedness theory of steady incompressible jet flow in a de Laval type nozzle with given end pressure at the outlet. The main results show that for any given incoming mass flux Q > 0 in the upstream and end pressure at the outlet, there exists an admissible interval to the Bernoulli’s constant, if the Bernoulli’s constant lies in the interval, there exists a unique smooth incompressible jet flow issuing from the nozzle. Moreover, the free boundary of the jet flow initiates smoothly from the surface of the divergent area of the de Laval nozzle. In particular, it is shown that the initial point of the free boundary lies behind the throat of the de Laval nozzle wall and varies continuously and monotonically with respect to the Bernoulli’s constant. As a direct corollary, imposing initial point of the free boundary on the divergent part of nozzle wall, there exists a unique incompressible jet for given incoming mass flux Q > 0 and pressure Pe at the outlet. This work is inspired by the significant works (Alt et al. in Commun Pure Appl Math 35:29–68, 1982; Arch Rational Mech Anal 81:97–149, 1983) for the incompressible jet flow imposing the initial point of the free boundary at the endpoint of the nozzle.

Numerical Investigation of Steady and Harmonic Vortex Generator Jets Flow Separation Control

Active flow control of canonical laminar separation bubbles by steady and harmonic vortex generator jets (VGJs) was investigated using direct numerical simulations. Both control strategies were found to be effective in controlling the laminar boundary-layer separation. However, the present results indicate that using the same blowing amplitude, harmonic VGJs were more effective and efficient at reducing the separated region than the steady VGJs considering the fact that the harmonic VGJs use less momentum than the steady case. For steady VGJs, longitudinal structures forming immediately downstream of the injection location led to the formation of hairpin-type vortices, causing an earlier transition to turbulence. Symmetric hairpin vortices were shown to develop downstream of the forcing location for the harmonic VGJs, as well. However, the increased control effectiveness for harmonic VGJs’ flow control strategy is attributed to the fact that the shear-layer instability mechanism was exploited. As a result, disturbances introduced by VGJs were strongly amplified, leading to the development of large-scale coherent structures, which are very effective at increasing the momentum exchange, thus limiting the separated region.

Jet formation in salt-finger convection: a modified Rayleigh–Bénard problem

Large-scale coherent structures such as jets in Rayleigh–Bénard convection and related systems are receiving increasing attention. This paper studies, both numerically and theoretically, the process of jet formation in two-dimensional salt-finger convection. The approach utilizes an asymptotically derived system of equations referred to as the modified Rayleigh–Bénard convection (MRBC) model, valid in the geophysically and astrophysically relevant limit in which the solute diffuses much more slowly than heat. In these equations, convection is driven by a destabilizing salinity gradient while the effects of the stabilizing temperature gradient manifest themselves as an additional anisotropic dissipation acting on large scales. The MRBC system is specified by two external parameters: the Schmidt number $\mathit{Sc}$ (ratio of viscosity to solutal diffusivity) and the Rayleigh ratio $\mathit{Ra}$ (ratio between the Rayleigh numbers of the destabilizing solutal stratification and the stabilizing thermal stratification). Two distinct $\mathit{Ra}$ regimes are explored for fixed $\mathit{Sc}=1$. In all cases studied the system develops a horizontal jet structure that is maintained self-consistently by turbulent fluctuations, but coarsens over time. For intermediate Rayleigh ratios (e.g. $\mathit{Ra}=6$), the MRBC model captures the relaxation oscillations superposed on the jet structure observed at similar parameter values in direct numerical simulations of the primitive equations. For smaller Rayleigh ratios (e.g. $\mathit{Ra}=2$), a regime for which direct numerical simulation of the primitive equations is difficult because of the presence of fast gravity waves, the MRBC model reveals the existence of statistically steady jets whose properties are studied in detail. Three hierarchical models, the MRBC and further reductions in the form of quasilinear and single-mode approximations, are used to confirm that jets form and are sustained as a result of the interaction between fluctuations (salt fingers) and large-scale horizontally averaged horizontal flows (jets). Even though the small-scale structures exhibited by the three models exhibit clear differences, all three produce the same power-law spectrum of the mean fields at large vertical scales: in all, the spectrum of the mean streamfunction scales as $m^{-3}$ and the mean salinity field scales as $m^{-1}$, with $m$ the vertical wavenumber. A theoretical explanation of these observations based on the dominant balances in the mean and fluctuation equations is provided. As a consequence, the jets have a zigzag profile, a conclusion that is consistent with numerical simulations. Based on numerical observations, a three-component phenomenological model consisting of a linearly growing mode, a linearly damped mode and a mean mode is proposed to explain the observed transition from statistically steady jet structure to jets with superposed oscillations that takes place with increasing Rayleigh ratio.

LES of primary breakup of pulsed liquid jet in supersonic crossflow

The injection of a pulsed liquid jet into supersonic air flow is a promising approach to improving the fuel atomization performance in a Scramjet engine. Therefore, the primary breakup of a pulsed liquid jet in supersonic crossflow is numerically investigated in the present paper. A two-phase flow Large Eddy Simulation (LES) algorithm is developed for simulations of liquid jet atomization in supersonic gas flow. A coupled Level Set and Volume of Fluid (VOF) method is used to track the interface deformation and disintegration. The supersonic gas flow is solved using a compressible flow solver while the liquid phase is solved by an incompressible flow solver. Appropriate boundary conditions are specified at the interface for both solvers to correctly capture the interaction between the gas and liquid phases. The primary atomization of a steady liquid jet with the same average mass flow rate as the pulsed jet is also simulated as a benchmark test case. The liquid velocity pulsation produces a very different primary atomization morphology in comparison with the steady liquid jet, which significantly enhances the primary breakup process. It is observed that Rayleigh-Taylor instability dominates the development of surface waves for the steady liquid jet. For the pulsed liquid jet, the liquid column deformation induced by the liquid velocity pulsation determines the wavelength of the surface waves and thus the liquid jet breakup location. In comparison with the steady liquid jet, the penetration of the pulsed liquid jet increases by 20%, and the width of the wake zone expands by 25%, resulting in improved atomization and mixing performance.

Suppression of Cavity Flow Oscillations via Three-Dimensional Steady Blowing

This paper presents an investigation of the flow physics and control of cavity flow oscillations using a three-dimensional (3-D) array of steady jets located near the cavity leading edge. The array injects 3-D, steady flow normal to the freestream to suppress the fluctuating surface pressure in a rectangular cavity with a length-to-depth ratio of 6 for Mach 0.3 to 0.7. Sixteen configurations are assessed for their suppression as a function of the aggregate momentum coefficient , spatial duty cycle , and dimensionless wavelength . Significant reductions of fluctuating surface pressure are observed. Schlieren and particle image velocimetry are performed to investigate the baseline and controlled flows. Companion large-eddy simulations with spanwise periodic boundary conditions at Mach 0.6 generally agree with the experiments, despite a significant difference in the Reynolds numbers. The simulations show that control reduces the pressure fluctuations inside the entire cavity, albeit at a higher level of . Spanwise wavelike structures produced by the control input distort the shear layer, inhibit the growth of large-scale vortical structures, and reduce the strength and length scale of turbulent fluctuations near the impingement region. A slot-configuration design guide is provided, which compares favorably with the limited available data in the literature.

Properties of a sweeping jet emitted from a fluidic oscillator

This experimental study investigates the flow field and properties of a sweeping jet emitted from a fluidic oscillator into a quiescent environment. The aspect ratio of the outlet throat is 1. Stereoscopic particle image velocimetry is employed to measure the velocity field plane-by-plane. Simultaneously acquired pressure measurements provide a reference for phase correlating the individual planes yielding three-dimensional, time-resolved velocity information. Lagrangian and Eulerian visualization techniques illustrate the phase-averaged flow field. Circular head vortices, similar to the starting vortex of a steady jet, are formed repetitively when the jet is at its maximum deflection. The quantitative jet properties are determined from instantaneous velocity data using a cylindrical coordinate system that takes into account the changing deflection angle of the jet. The jet properties vary throughout the oscillation cycle. The maximum jet velocity decays much faster than that of a comparable steady jet indicating a higher momentum transfer to the environment. The entrainment rate of the spatially oscillating jet is larger than for a steady jet by a factor of 4. Most of the mass flow is entrained from the direction normal to the oscillation plane, which is accompanied by a significant increase in jet depth compared to a steady jet. The high entrainment rate results from the enlarged contact area between jet and ambient fluid due to the spatial oscillation. The jet’s total force exceeds that of an idealized steady jet by up to 30 %. The results are independent of the investigated oscillation frequencies in the range from 5 to 20 Hz.

Trajectory of a synthetic jet issuing into high-Reynolds-number turbulent boundary layers

Synthetic jets are zero-net-mass-flux actuators that can be used in a range of flow control applications. For some applications, the scaling of the trajectory of the jet with actuation and cross-flow parameters is important. This scaling is investigated for changes in the friction Reynolds number, changes in the velocity ratio (defined as the ratio between the mean jet blowing velocity and the free-stream velocity) and changes in the actuation frequency of the jet. A distinctive aspect of this study is the high-Reynolds-number turbulent boundary layers (up to $Re_{\unicode[STIX]{x1D70F}}=12\,800$) of the cross-flow. To our knowledge, this is the first study to investigate the effect of the friction Reynolds number of the cross-flow on the trajectory of an (unsteady) jet, as well as the first study to systematically investigate the scaling of the trajectory with actuation frequency. A broad range of parameters is varied (rather than an in-depth investigation of a single parameter) and the results of this study are meant to indicate the relative importance of each parameter rather than the exact influence on the trajectory. Within the range of parameters explored, the critical ones are found to be the velocity ratio as well as a non-dimensional frequency based on the jet actuation frequency, the cross-flow velocity and the jet dimensions. The Reynolds number of the boundary layer is shown to have only a small effect on the trajectory. An expression for the trajectory of the jet is derived from the data, which (in the limit) is consistent with known expressions for the trajectory of a steady jet in a cross-flow.

Numerical investigation of a pulsed reaction control jet in hypersonic crossflow

This paper presents a numerical study on the flow structures developed when a pulsed reaction control jet is operated in a hypersonic crossflow with a laminar boundary layer. Understanding these flow structures is important to the design of reaction control jets and scramjet fuel injectors. Implicit large-eddy simulations were performed with a round, sonic, perfect air jet issuing normal to a Mach 5 crossflow over a flat plate, at a jet-to-crossflow momentum ratio of 5.3 and a pressure ratio of 251, and with square-wave pulsing at Strouhal numbers of 1/6 to 1/3, based on jet diameter and free-stream velocity. Pulsing the jet allows the shock structure to partially collapse when the jet is off. This shock collapse affects the shedding frequency of shear-layer vortices, the formation of shear-layers downstream of the jet outlet, and the formation of longitudinal counter-rotating vortices. The lead shocks formed at jet start-up allow deeper penetration by increasing the effective jet-to-crossflow momentum ratio near the jet outlet and by preventing interaction between hairpin vortices. Normalised penetration was increased by a maximum of 68% compared with the steady jet. Pulsing also provides a higher jet interaction force per unit mass flow rate compared with a steady jet, with a 52% increase recorded at a 33% duty cycle. Temporal and spatial variations of surface pressure are important for reaction control applications and have been quantified. Pressure distribution depends strongly on duty cycle, and higher interaction force per unit mass flow rate was observed in cases with low duty cycle.

The Experimental Investigation of Impinging Heat Transfer of Pulsation Jet on the Flat Plate

A series of tests were performed for the pulsating jet impingement heat transfer by varying the Reynolds number (5000 ≤ Re ≤ 20,000), operation frequency (10 Hz ≤ f ≤ 25 Hz), and dimensionless nozzle-to-surface distance (1≤H/d≤8) while fixing the duty cycle (DC) = 0.5(280 measurement data in total). Specific attention was paid to examine the relationship between the pulsating jet impingement and the steady jet impingement. By using a modified Strouhal number (Sr(H/d)), the test data are analyzed according to three classifications of the enhancement factors a = Nupulsation jet/Nusteady jet (such as a ∈ (Min,0.899), a ∈ (0.95, 1.049) and a ∈ (1.1, Max)). The results show that the identification of pulsating jet impingement in related to the steady jet impingement is suitable by using the modified Strouhal number (Sr(H/d)). Within the scope of this study, the most possibilities for the heat transfer enhancement by using pulsating jet impingement are suggested as the following conditions: Re ≤ 7500 and Sr(H/d) ≥ 0.04, Re ≥ 17500, and 0.01 ≤ Sr(H/d) ≤ 0.03; 10 Hz ≤ f ≤ 20 Hz and Sr(H/d) ≥ 0.04; H/d ≥ 6 and most of current Sr(H/d). While under such conditions, 7500 ≤ Re ≤ 15,000 and Sr(H/d) ≤ 0.02; f ≥ 20 Hz and Sr(H/d) ≤ 0.04; H/d ≤ 2 and Sr(H/d) ≤ 0.02, the pulsating jet impingement makes the heat transfer weaker than the steady jet impingement more obviously.

Sweeping jet impingement heat transfer on a simulated turbine vane leading edge

With the development of additive manufacturing technology, it is now possible to design complex and integrated internal cooling architecture for a gas turbine engine. In search of a spatially uniform heat transfer at the leading edge of a turbine nozzle guide vane, a sweeping jet impingement cooling strategy was proposed. Experiments were conducted in a low-speed wind tunnel to investigate sweeping jet impingement cooling in a faired cylinder leading edge model at an engine-relevant Biot number (Bi). Sweeping jets were generated with additively manufactured fluidic oscillator and steady jets were produced by a cylindrical orifice (with length to diameter ratio of 1). Both sweeping and steady jets were studied at varying mass flow rates, jet-to-wall spacing (H/D), jet pitch (P/D), and freestream turbulence. The effect of varying aspect ratio (AR) of the sweeping jet geometries was also studied. The overall cooling effectiveness of each configuration was estimated using infrared thermography (IR) measurements of the external surface temperature of the leading edge model. The sweeping jet provided higher overall cooling effectiveness values compared to steady jet in specific configurations. The pressure drop across each jet was also measured for each geometry, and the sweeping jet shows comparable pressure drop to steady jet.

An investigation of the interactions between impulsively started and steady supersonic jets

The ignition of the solid rocket booster strap-on and the following IOP wave have a severe influence on the dynamic as well as the acoustic loads experienced by a launch vehicle during lift-off. The jet from the strap-on interacts with the core jet and its established flow over the jet blast deflector, influencing the acoustic field experienced by the launch vehicle. The existing literature provides very little understanding of such interactions. This work investigates the interaction between the jet from SRB and the core, by simulating them with an impulsively started supersonic jet in close proximity to another established jet. While the flow for the core nozzle was allowed directly from the settling chamber, a novel approach using a quick opening valve was used for initiating the flow through the strap-on nozzle. The evolution of a strong shock wave emanating from the strap-on nozzle and the ensuing vortex ring, their interaction with the core jet flow, etc., was captured using schlieren. The results document the fluid dynamic interactions such as the evolution of a strong shock wave emanating from the strap-on nozzle and the ensuing vortex ring, their interaction with the core jet flow, etc., using flow visualizations and acoustic measurements.

Drag and heat flux reduction induced by the pulsed counterflowing jet with different periods on a blunt body in supersonic flows

In the current study, three different kinds of pulsed jets with the period being 0.5 ms, 1.0 ms and 2.0 ms are established, and sinusoidal waveforms are used in all three pulsed jets. The pulsed counterflowing jets with the same amplitude but different periods on the nose of a blunt body in supersonic flows are investigated numerically, and an axisymmetric numerical simulation model of the counterflowing jet on the supersonic vehicle nose-tip is established. The obtained results show that the wall Stanton number and surface pressure change periodically with the pulsed jet, and the variations of the parameters show a strong hysteresis phenomenon. The hysteresis phenomenon becomes less significant as the period increases. At the same time, a better drag and heat flux reduction is obtained under larger period pulsed jet conditions. With the increase of the period of the pulsed jet, there is a significant decline in the maximum peak values of the wall Stanton number and surface pressure. Compared with the steady jet, the pulsed jet is more effective in heat flux reduction, but the drag reduction of the pulsed jet is less effective than the steady jet.

Generation characteristics of a metal ion plasma jet in vacuum discharge

To improve the performance of a metal ion plasma jet in vacuum discharge, an anode-insulated cone-cylinder electrode with insulating sleeve is proposed in this paper. Discharge characteristics and generation characteristics of plasma of the electrode are investigated, effects of diameter of insulating sleeve, variety of cathode material and length of the insulating sleeve on characteristics of metal ion plasma jet are discussed. Results indicate that a directional and steady plasma jet is formed by using the novel electrode with insulating sleeve under high vacuum conditions. Moreover, the properties of metal ion plasma jet are improved by using the aluminum cathode and thin and long insulating sleeve. The study provides strong support for research of vacuum metal ion plasma thruster and ion implantation technology.