Global characteristics of an ATON stationary plasma thruster operating with krypton and xenon

The global characteristics of an ATON stationary plasma thruster operating on xenon and krypton are investigated. It is shown that, with krypton, the thrust at the same mass flow rate of the working gas is greater and the efficiency is somewhat lower than those with xenon. An efficiency of ～60% was achieved with krypton for the specific impulse attaining 3000 s. The jet divergence is ～±22° for krypton and ～±11° for xenon.     

Stationary plasma thrusters operate in space

The first ÉOL-1 flight propulsion system with a stationary plasma thruster created at the Fakel Experimental and Design Bureau (EDB) on the basis of an experimental thruster designed and tested at the Kurchatov Institute of Atomic Energy is described. Subsequent versions of the ÉOL-type systems designed at the Fakel EDB using M-70, M-100, and other thrusters are reviewed. The current state of work on stationary plasma thrusters in the world is analyzed. The Phobos-Grunt project, whose aim is to deliver soil samples from Phobos and which implies the use of stationary plasma thrusters, is discussed.     

Influence of Xenon and Krypton Flow Rates through the Acceleration Channel of Morozov’s Stationary Plasma Thruster on the Thrust Efficiency

Plasma Physics Reports - Morozov’s stationary plasma thrusters (SPTs) operating with xenon have been successfully used for many years in space technology. At the same time, due to the high...     

A simple model to determine the interrelation between the integral characteristics of hall thrusters

A simple model to determine the interrelation between the integral characteristics of Hall thrusters with an anode layer is proposed. The model includes the equation describing the balance of forces acting on the Hall current region, as well as the relationship between the current of accelerated ions and the rate of working gas consumption. For fixed geometrical characteristics of a specific Hall thruster, this model allows one to interrelate the main integral characteristics of the thruster, such as the accelerating voltage, the magnetic field, the propellant flow rate, and the current of accelerated ions. The results of calculations for TAL-WSF/D-55—one of the most widely used Hall thrusters with an anode layer—are presented. The domain of existence of the discharge in the channel of the Hall thruster is analyzed. It is shown that taking into account kinetic effects of neutral particle expansion and working gas preheating lead to a decrease in the current of accelerated ions and the engine thrust.     

Plasma electron-emitting source in a low-pressure beam-plasma discharge in a stationary plasma thruster

A new type of plasma electron-emitting source capable of increasing the temperature of plasma electrons behind the edge of a stationary plasma thruster (SPT) to 7–15 eV has been developed and investigated experimentally. For the same parameters of the main discharge, the thrust, the thrust efficiency, the mass use factor, and the lifetime of the “SPT anode unit-plasma electron-emitting source” assembly are found to increase substantially as compared to a thruster equipped with a conventional cathode compensator. Simultaneously, the neutral particle pressure required for the existence of self-consistent distributions of the electric field and charged particle density in the drift space of the neutralized ion beam decreases appreciably. It is shown that the volume of the region in which primary slow ions are produced increases with increasing ionization frequency. Three additional channels for discharge control are implemented. The ranges in which the discharge parameters can be controlled are extended.     

Wake Vortex Structure Characteristics of a Flexible Oscillating Fin

We compute the wake of a two-dimensional and three-dimensional flexible fin in an unsteady flow field with heaving and pitching motions using FLUENT. Deflexion mode is used for a non-uniform cantilever beam with non-uniformly distributed load. The effect of chordwise deflexion length on the characteristics of propulsion is discussed for two-dimensional flexible fin. The thrust coefficient decreases, propulsive efficiency increases and the intensity of turbulence attenuates gradually as the deflexion length increases. For a three-dimensional flexible fin, the intensity of the vortex in the plane of symmetry is higher than that in the plane at 3/4 span length of the caudal fin. But the propulsive perform.ance achieved is not what we expected with the given deflexion mode.     

Study of low-temperature plasma between rotating electrodes

Results are presented from experimental studies of the electrophysical and spatiotemporal characteristics of a dielectric barrier discharge operating in atmospheric-pressure air in a discharge cell with a dielectric barrier in the form of a rotating disc. One of the electrodes of the discharge cell was stationary and placed at a certain distance from the dielectric surface, and the following two versions of the second electrode were used: (i) a metal disc electrode was attached to the surface of the rotating dielectric disc, while on the opposite surface of the disc, there was a rectangular strip electrode that was at the same potential as a metal disc electrode and had a sliding contact with the dielectric; (ii) only the strip electrode with the sliding contact was connected to the high-voltage source, while the metal disc electrode was disconnected. Due to barrier rotation, the discharge operated in a pulse mode, although it was supplied from a dc voltage source. The current-voltage characteristic of such a dielectric barrier discharge was measured and analyzed. The number of microdischarge channels arising at the stationary electrode, the geometrical parameters of the microdischarge channels, and the discharge current were studied as functions of the supplied voltage, the distance between the stationary electrode and the dielectric surface, and the rotation velocity of the barrier disc.     

Model of the near-wall conductivity in the vicinity of a macroscopically inhomogeneous, mirror-reflecting surface

A study is made of the interaction of the electron component of a low-density plasma with a macroscopically inhomogeneous, mirror-reflecting surface in mutually orthogonal electric and magnetic fields. The collisionless kinetic equation is solved analytically in the (2R+3V)-dimensional space. A nontrivial structure of the nascent near-wall currents is revealed, and their two-dimensional distribution is analyzed in detail. From the standpoint of practical applications, attention is focused on the near-wall conductivity in a stationary plasma thruster. The results obtained agree with the available experimental data. Moreover, the investigations described here provide a basis for the study of the possibility of tailoring the insulator in the channel for the purpose of suppressing anomalous erosion and ensuring the required operating period of plasma thrusters. __________ Translated from Fizika Plazmy, Vol. 28, No. 2, 2002, pp. 180–187. Original Russian Text Copyright ￠ 2002 by Kozlov.     

A general law for animal locomotion?

The propulsion system of animals that fly or swim are quite different from each other in their morphology and function, yet the propulsive efficiency could be maximized by a surprising similarity in the fine tuning of flapping frequency, amplitude and forward speed, according to a new study by Taylor et al. This conclusion was based on an analysis of the Strouhal number, which is a dynamic similarity index relevant to propulsion that relies on vortex shedding for thrust generation. Such fine-tuning of the propulsive system suggests possible consequences for physiological and ecological adaptations related to, for example muscle operating frequency and optimal speed of muscle contraction.     

Swimming dynamics and propulsive efficiency of squids throughout ontogeny

Squids encounter vastly different flow regimes throughout ontogeny as they undergo critical morphological changes to their two locomotive systems: the fins and jet. Squid hatchlings (paralarvae) operate at low and intermediate Reynolds numbers (Re) and typically have rounded bodies, small fins, and relatively large funnel apertures, whereas juveniles and adults operate at higher Re and generally have more streamlined bodies, larger fins, and relatively small funnel apertures. These morphological changes and varying flow conditions affect swimming performance in squids. To determine how swimming dynamics and propulsive efficiency change throughout ontogeny, digital particle image velocimetry (DPIV) and kinematic data were collected from an ontogenetic range of long-finned squid Doryteuthis pealeii and brief squid Lolliguncula brevis swimming in a holding chamber or water tunnel (Re = 20-20 000). Jet and fin wake bulk properties were quantified, and propulsive efficiency was computed based on measurements of impulse and excess kinetic energy in the wakes. Paralarvae relied predominantly on a vertically directed, high frequency, low velocity jet as they bobbed up and down in the water column. Although some spherical vortex rings were observed, most paralarval jets consisted of an elongated vortical region of variable length with no clear pinch-off of a vortex ring from the trailing tail component. Compared with paralarvae, juvenile and adult squid exhibited a more diverse range of swimming strategies, involving greater overall locomotive fin reliance and multiple fin and jet wake modes with better defined vortex rings. Despite greater locomotive flexibility, jet propulsive efficiency of juveniles/adults was significantly lower than that of paralarvae, even when juvenile/adults employed their highest efficiency jet mode involving the production of periodic isolated vortex rings with each jet pulse. When the fins were considered together with the jet for several juvenile/adult swimming sequences, overall propulsive efficiency increased, suggesting that fin contributions are important and should not be overlooked in analyses of the swimming performance of squids. The fins produced significant thrust and consistently had higher propulsive efficiency than did the jet. One particularly important area of future study is the determination of coordinated jet/fin wake modes that have the greatest impact on propulsive efficiency. Although such research would be technically challenging, requiring new, powerful, 3D approaches, it is necessary for a more comprehensive assessment of propulsive efficiency of the squid dual-mode locomotive system.     

Stability of Ion Flow and Role of Boundary Conditions in a Simplified Model of the E × B Plasma Accelerator with a Uniform Electron Mobility

Plasma Physics Reports - Resistive oscillations of axial plasma with ionization effects are analyzed in configuration similar to the Hall effect thrusters. From analysis of stationary equations we...     

Numerical Study of Propulsion Mechanism for Oscillating Rigid and Flexible Tuna-Tails

Numerical study on the unsteady hydrodynamic characteristics of oscillating rigid and flexible tuna-tails in viscous flow-field is performed.Investigations are conducted using Reynolds-Averaged Navier-Stokes (RANS) equations with a moving adaptive mesh.The effect of swimming speed,flapping amplitude,frequency and flexure amplitude on the propulsion performance of the rigid and flexible tuna-tails are investigated.Computational results reveal that a pair of leading edge vortices develop along the tail surface as it undergoes an oscillating motion.The propulsive efficiency has a strong correlation with various locomotive parameters.Peak propulsive efficiency can be obtained by adjusting these parameters.Particularly,when input power coefficient is less than 2.8,the rigid tail generates larger thrust force and higher propulsive efficiency than flexible tail.However,when input power coefficient is larger than 2.8,flexible tail is superior to rigid tail.     

On the longitudinal distribution of electric field in the acceleration zones of plasma accelerators and thrusters with closed electron drift

The long-term experience in controlling the electric field distribution in the discharge gaps of plasma accelerators and thrusters with closed electron drift and the key ideas determining the concepts of these devices and tendencies of their development are analyzed. It is shown that an electrostatic mechanism of ion acceleration in plasma by an uncompensated space charge of the cloud of magnetized electrons “kept” to the magnetic field takes place in the acceleration zones and that the electric field distribution can be controlled by varying the magnetic field in the discharge gap. The role played by the space charge makes the mechanism of ion acceleration in this type of thrusters is fundamentally different from the acceleration mechanism operating in purely electrostatic thrusters.     

Specific features of an electric discharge operating between an electrolytic anode and a metal cathode

Results are presented from experimental studies of a high-current electric discharge operating between an St45 steel cathode and a service water anode in a wide range of air pressures. Peculiarities of discharge ignition and specific features of cathode and anode spots were revealed. The behavior of the current density on a service water anode was investigated for the first time. Comparison of the current densities j on the steel cathode and service water anode shows that, in the parameter range under study, Hehl’s law is not satisfied on the water anode. The two-dimensional distribution of the potential inside and on the surface of the service water anode was measured.     

Mechanical efficiency of cycling with a new developed pedal-crank

The mechanical efficiency of cycling with a new pedal-crank prototype (PP) was investigated during an incremental test on a stationary cycloergometer. The efficiency values were compared with those obtained, in the same experimental conditions and with the same subjects, by using a standard pedal-crank system (SP). The main feature of this prototype is that its pedal-crank length changes as a function of the crank angle being maximal during the pushing phase and minimal during the recovery one. This variability was expected to lead to a decrease in the energy requirement of cycling since, for any given thrust, the torque exerted by the pushing leg is increased while the counter-torque exerted by the contra-lateral one is decreased. Whereas no significant differences were found between the two pedal-cranks at low exercise intensities (w*=50-200 W), at 250-300 W the oxygen uptake (V*O2, W) was found to be significantly lower and the efficiency (eta=w*/V*O2) about 2% larger (p<0.05, Wilcoxon test) in the case of PP. Even if the measured difference in efficiency was rather small, it can be calculated that an athlete riding a bicycle equipped with the patented pedal-crank could improve his 1h record by about 1 km.     

Flipper bone distribution reveals flexible trailing edge in underwater flying marine tetrapods

Hydrofoil-shaped limbs (flipper-hydrofoils) have evolved independently several times in secondarily marine tetrapods and generally fall into two functional categories: (1) those that produce the majority of thrust during locomotion (propulsive flipper-hydrofoils); (2) those used primarily to steer and resist destabilizing movements such as yaw, pitch, and roll (controller flipper-hydrofoils). The morphological differences between these two types have been poorly understood. Theoretical and experimental studies on engineered hydrofoils suggest that flapping hydrofoils with a flexible trailing edge are more efficient at producing thrust whereas hydrofoils used in steering and stabilization benefit from a more rigid one. To investigate whether the trailing edge is generally more flexible in propulsive flipper-hydrofoils, we compared the bone distribution along the chord in both flipper types. The propulsive flipper-hydrofoil group consists of the forelimbs of Chelonioidea, Spheniscidae, and Otariidae. The controller flipper-hydrofoil group consists of the forelimbs of Cetacea. We quantified bone distribution from radiographs of species representing more than 50% of all extant genera for each clade. Our results show that the proportion of bone in both groups is similar along the leading edge (0–40% of the chord) but is significantly less along the trailing edge for propulsive flipper-hydrofoils (40–80% of the chord). Both flipper-hydrofoil types have little to no bony tissue along the very edge of the trailing edge (80–100% of the chord). This suggests a relatively flexible trailing edge for propulsive flipper-hydrofoils compared to controller flipper-hydrofoils in line with findings from prior studies. This study presents a morphological correlate for inferring flipper-hydrofoil function in extinct taxa and highlights the importance of a flexible trailing edge in the evolution of propulsive flipper-hydrofoils in marine tetrapods.     

Swimming abilities of ammonites and limitations

Using some typial ammonites from the Posidonia shales, the aperture orientation, the ideal direction of propulsive thrust, the stability and the buoyancy of the living animals and of the empty shells were investigated as a function of the body chamber length. The emerging limitations indicate that ammonites were hardly suited for a nectonic mode of life. Only in case of favourable conditions empty shells could ascend to the surface and drift.     

Biomechanics of swimming in the pufferfish Diodon holocanthus: propulsive momentum enhancement is an adaptation for thrust production in an undulatory median and paired-fin swimmer

A form of large-amplitude elongated-body theory appropriate for the analysis of undulatory fins attached to a rigid body of elliptical section suggests a benefit due to momentum enhancement relative to the fins on their own. This theoretical prediction is experimentally confirmed for the first time. Theoretical momentum enhancement factors for Diodon holocanthus (2.2 and 2.7 for the median and pectoral fins, respectively) compared well to inferred thrust values determined from particle-image velocimetry (PIV) wake measurements (2.2-2.4 and 2.7-2.9). Caudal fin mean theoretical thrust was not significantly different from measured (PIV) values (n = 24, P > 0.05), implying no momentum enhancement. Pectoral-fin thrust was half that of the median and caudal fins due to high fin-jet angles, low circulation and momentum. Average total fin thrust and fish drag were not significantly different (n = 24, P > 0.05). Vortex rings generated by the fins were elliptical, with size dependent on fin chord and stroke amplitude. Hydrodynamic advantages (thrust enhancement at no cost to hydrodynamic efficiency, reduction of side forces minimizing energy wasting yawing motions and body drag) are probably common among rigid-bodied organisms propelled by undulatory fins. A trade-off between momentum enhancement and the rate of momentum generation (thrust force) sets a practical limit to the former. For small fins whilst momentum enhancement is high, absolute thrust is low. In addition, previously suggested limitations on thrust enhancement set by reductions in propulsive force associated with progressive reductions in fin wavelength are found to be biologically unrealistic.