Despite its affordability, the krypton Hall-effect thruster in applications always had problems in regard to performance. The reason for this degradation is studied from the perspective of the nearwall conductivity of electrons. Using the particle-in-cell method, the sheath oscillation characteristics and its effect on near-wall conduction are compared in the krypton and xenon Hall-effect thrusters both with wall material composed of BNSiO 2 . Comparing these two thrusters, the sheath in the krypton-plasma thruster will oscillate at low electron temperatures. The near-wall conduction current is only produced by collisions between electrons and wall, thereby causing a deficiency in the channel current. The sheath displays spatial oscillations only at high electron temperature; electrons are then reflected to produce the non-oscillation conduction current needed for the krypton-plasma thruster. However, it is accompanied with intensified oscillations. V C 2014 AIP Publishing LLC. INTRODUCTIONAt present, using Hall-effect thrusters in interplanetary missions and geostationary satellites with affordable propellants can reduce costs and improve economics. Optional propellants include gases of argon, krypton, nitrogen, and nitrogen dioxide. Although the atomic masses of these gases are smaller and the degrees of first ionization are higher than xenon, thereby yielding lower propulsive efficiency, these propellants are more affordable. 1 The Hall-effect thruster is universally applicable in many countries involved in aeronautics and in which giving the krypton-plasma thruster greater research attention. [2][3][4] Although previous studies show that compared with xenon, the thruster efficiency is low with krypton, some studies show that improvements in efficiency can be made in propellant utilization rate, along with other means, which approach the efficiency of xenon. [5][6][7][8]12 Other research shows that thruster performance based on krypton is significantly lower than that on xenon. 6,[9][10][11] With a low utilization rate of krypton, krypton (with a decrease of 37% in atomic mass) relative to xenon under normal conditions, the thrust decreases 20%-30% and the specific impulse decreases 37%. 13 Previous studies have concluded that the main factor of krypton's low efficiency is its low propellant utilization rate. To study the reason for this low efficiency, it is necessary to study the plasma in the thruster's discharge channel. 14 Estimates of classical conduction produced by collisions between electrons and atoms is far less than experimental results; that is, other unusual conduction occurs allowing electrons to cross magnetic field lines. 15 Some researchers believe that this unusual conduction is due to collective oscillation in the plasma of the thruster, which is called Bohm conduction. Bohm conduction is used to explain the reason why the current is greater than that produced solely by collision between electrons and atoms in discharge devices using plasma with a high degree of ionization. The Bohm conduct...
The behaviors of shock-accelerated heavy gas bubbles are numerically investigated, focusing on clarifying the forming mechanisms of the bubble jets in different types. The present study categorizes heavy bubble jets into two types, regular jets, and irregular jets. The present shock-accelerated multi-component flows are simulated by solving inviscid compressible Euler equations. An upwind characteristic space-time conservation element solution element scheme is adopted, and a five-equation model is used to treat the gas interface. Bubbles of R22, SF6, and Kr in ambient N2 and air are examined, and the incident shock Mach numbers are 1.1 and 1.23. The numerical results demonstrate that the bubble jet formation and its shape are very sensitive to the test gas species and incident shock strength. It is found that the tiny upstream jet formed in the single-shocked SF6/air scenario results from a very small Mach stem impingement onto the bubble upstream interface, the type II shock-shock interaction features the flow mechanism. While the large upstream jet formed in the re-shock SF6/air scenario is a combined result of the re-shock convergence and later vortex stretching. For the complex Kr/air scenario, the upstream jet results from the vorticity-induced inward jet stretching, and the downstream hollow jet results from the slip line guided tip extension. The measurements of bubble volumes, gas mixings, and material line lengths suggest that, although the jet formation greatly changes the bubble morphology, it makes a minor contribution to the bubble overall integral properties.
The flow patterns in a large-expansion-ratio annular expansion–deflection (ED) nozzle are numerically investigated, focusing on the flow mechanisms underlying the sudden thrust efficiency (η) dropping phenomenon. The objective of the present work is to provide a physical understanding of the ED nozzle flow physics responsible for the nozzle performance variation. The simulations are performed by solving the Reynolds averaged Navier–Stokes equations in combination with the one-equation Spalart–Allmaras turbulence model. The Advection Upstream Splitting Method is used to discretize the convective fluxes, and the second-order central scheme is used to discretize the viscous fluxes. The present investigation demonstrates that two flow mechanisms exist, which can cause the sudden η dropping: one is supersonic flow impingement at the nozzle exit, and the other is the formation of the internal normal shock. The pintle arc radius downstream of the throat plays an important role in determining the size and redirection of the supersonic core flow region, thus influencing the overall nozzle performance. A large radius dimension gives a higher η value at the first rising stage, a large dropping nozzle pressure ratio (NPR), and a large mode transition NPR. Interestingly, a cap shock is proved possible in the current large-expansion-ratio ED nozzle, in which the near-shroud shock acts as the internal shock in the traditional thrust-optimized or parabolic nozzles.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.