Rarefaction

About: Rarefaction is a research topic. Over the lifetime, 1852 publications have been published within this topic receiving 26943 citations.

Direct simulation Monte Carlo investigation of mixed supersonic–subsonic flow through micro-/nano-scale channels

Abstract: The main goal in this study is to provide deep physical descriptions on the behaviour of supersonic micro-/nano-channel flow using the direct simulation Monte Carlo method. We found some unique physical aspects of micro-/nano-flows including mixed supersonic–subsonic regimes in constant-area ducts. This mixed regime is due to the formation of entrance shocks and their reflection from the thick boundary layer developed in a rarefied medium. We studied the effects of Mach number, channel aspect ratio and flow rarefaction on the channel inflow condition. The effects of wall thermal state on flow behaviour and shock wave structures were also investigated.

Head-on Collision of a Detonation with a Planar Shock Wave

Abstract: The phenomenon that occurs when a Chapman–Jouguet (CJ) detonation collides with a shock wave is discussed. Assuming a one-dimensional steady wave configuration analogous to a planar shock–shock frontal interaction, analytical solutions of the Rankine–Hugoniot relationships for the transmitted detonation and the transmitted shock are obtained by matching the pressure and particle velocity at the contact surface. The analytical results indicate that there exist three possible regions of solutions, i.e. the transmitted detonation can have either strong, weak or CJ solution, depending on the incident detonation and shock strengths. On the other hand, if we impose the transmitted detonation to have a CJ solution followed by a rarefaction fan, the boundary conditions are also satisfied at the contact surface. The existence of these multiple solutions is verified by an experimental investigation. It is found that the experimental results agree well with those predicted by the second wave interaction model and that the transmitted detonation is a CJ detonation. Unsteady numerical simulations of the reactive Euler equations with both simple one-step Arrhenius kinetic and chain-branching kinetic models are also carried out to look at the transient phenomena and at the influence of a finite reaction thickness of a detonation wave on the problem of head-on collision with a shock. From all the computational results, a relaxation process consisting of a quasi-steady period and an overshoot for the transmitted detonation subsequent to the head-on collisions can be observed, followed by the asymptotic decay to a CJ detonation as predicted theoretically. For unstable pulsating detonations, it is found that, due to the increase in the thermodynamic state of the reactive mixture caused by the shock, the transmitted pulsating detonation can become more stable with smaller amplitude and period oscillation. These observations are in good agreement with experimental evidence obtained from smoked foils where there is a significant decrease in the detonation cell size after a region of relaxation when the detonation collides head-on with a shock wave.

Interaction of detonation and rarefaction waves in aluminum particles dispersed in oxygen

Abstract: The problem of interaction of a plane detonation wave with an adjacent rarefaction wave is studied on the basis of a mathematical model of detonation of aluminum particles dispersed in oxygen. The numerical solution is obtained within the framework of the one-velocity two-temperature approximation of the mechanics of heterogeneous media for the Chapman–Jouguet regime and strong and weak detonation regimes. It is shown that the Chapman–Jouguet regime and weak regimes with an internal singular point are self-sustained. Three intervals of the relaxation parameter (the ratio of the characteristic times of thermal relaxation and combustion) are determined. The detonation/rarefaction wave interaction results in the Chapman–Jouguet regime in the first interval, in decomposition of the detonation wave into a shock wave and a lagging combustion front with further loss of stability in the second interval, and in a weak detonation regime in the third interval.

Sonic rarefaction wave recoilless gun system

Abstract: A low recoil and low bore heat gun system provides a delayed pressure release mechanism for fired propellant charges in the rear gun barrel section. The delayed pressure release of the exhaust gases causes a sonic rarefaction wave along the length of the barrel bore to arrive at the exist end of the gun barrel at a predetermined time, generally coincident with the fired projectile.

Scaling parameters for hypersonic flow: correlation of sphere drag data

Abstract: Various parameters have been suggested as correlation parameters for high-speed rarefied flow, or as indicators of when rarefaction effects make the Navier-Stokes equations invalid. We consider Tsien's (1946) parameter, Cheng's (1961) rarefaction parameter, Bird's (1971) breakdown parameter, and a form of the viscous interaction parameter from shock-boundary layer theory. We show how all these parameters may be derived from the Boltzmann equation and interpreted in terms of the ratio of mean time between molecular collisions and a characteristic flow time, or as the ratio of typical shear stress to pressure in the flow. Tsien's parameter (M/sqrt{Re}) is proportional to the square root of (M Kn) or (S Kn) and is a better correlation parameter than the Knudsen number alone (Kn). Cheng's parameter (C*M^2/Re), as well as the closely related viscous interaction parameter, is a modified form of Tsien's parameter. The modification factor (C* = mu* T/mu T*), accounts for the effective molecular size or collision cross-section in a characteristic region of the flow. We consider the drag coefficient for spheres in hypersonic flow as calculated with DSMC by various authors and show that Cheng's appears to be the best correlation parameter for this data.