Abstract
When compressed gas is ejected from a nozzle into a low-pressure environment, the shock wave diffracts around the nozzle lip and a vortex loop will form. The phenomenon has been widely investigated in the continuum flow regime, but how the shock diffraction and vortex behave under rarefied flow conditions has not received as much attention. It is necessary to understand this transient flow in rarefied environments to improve thrust vector control and avoid potential contamination and erosion of spacecraft surfaces. This work provides numerical results of the vortex loop formation caused by shock wave diffraction around a 90° corner using the direct simulation Monte Carlo method and the compressible Navier–Stokes equations with the appropriate Maxwell velocity slip and the von Smoluchowski temperature jump boundary conditions. The Mach number and rarefaction effects on the formation and evolution of the vortex loop are discussed. A study of the transient structures of vortex loops has been performed using the rorticity concept. A relationship of mutual transformation between the rorticity and shear vectors has been discovered, demonstrating that the application of this concept is useful to understand vortex flow phenomena.
Highlights
The shock wave thickness at MS=1.6 predicted by direct simulation Monte Carlo (DSMC) is larger than that predicted by computational fluid mechanics (CFD) and this was observed in Ref. 7
The results show that the vortex loop in the rarefied condition still propagates, especially the cases in the slip flow regime
Transient DSMC and compressible CFD simulations has been performed, and comparisons have been made between the results from the dsmcFoamPlus and hy2Foam where the Knudsen number allowed
Summary
The continuous growth of applications for cost-effective micro-satellites in low Earth orbit (LEO) is leading to a requirement for specialized thruster systems that can provide thrusts in the micro- and mili-Newton range, in order to control their motions and orbits[8]. The hardware of electric propulsion systems, such as pulsed plasma thrusters, is more complicated than that of the non-electric type, which includes cold gas, liquid, and solid rocket propulsion systems[48]. The technologies used in electric propulsion systems must be validated to be reliable before extensive practical usage. Non-electric propulsion systems (e.g. cold gas micro-thrusters) have been deployed extensively for orbit transfer and manoeuvring due to their high reliability[33]. A common point shared by both of these propulsion technologies is that they operate by ejecting a mass of gas from a nozzle at high velocity to produce thrust
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