Periodical Oscillation of Combustion Induced by Oblique Shock Wave

Abstract

A numerical study was carried out for the combustion induced by oblique shock wave over a two-dimensional wedge of finite length. A compressible fluid dynamics code was used with a detailed hydrogen-oxygen combustion mechanism for the numerical study. For an off-attaching condition of oblique detonation waves (ODW) predicted by Rankine-Hugoniot theory with equilibrium chemistry, periodically oscillating combustion was induced by oblique shock wave for certain conditions. Investigation of the numerical results presents that the mechanism of the periodically oscillating combustion is an interaction between shock and reaction waves coupled with chemical kinetic effects. The oscillatory motion at the wedge surface was similar to the periodic motion of one dimensional detonation wave. For the investigation of the criterion of a periodically oscillating combustion, a series of numerical simulations were carried out for wedges of different lengths to change the ratio between fluid dynamic time scale and chemical time scale. At the offattaching condition of ODW predicted by RankineHugoniot theory with equilibrium chemistry, present results reveals three different regimes of combustion. (1) If a fluid dynamic residence time is shorter than a chemical induction time behind an oblique shock wave, combustion may not occur or incomplete shock-induced combustion was observed. (2) If a fluid dynamic residence time is longer than a chemical induction time behind an oblique shock wave, but the former is shorter than the later behind a bow shock wave at same Mach number, oblique shock wave still attaches at the wedge nose, even at the off-attaching condition of oblique detonation waves, and oscillatory combustion was observed. (3) If a fluid dynamic residence time is longer than a chemical induction time behind a bow shock wave, the oblique shock wave is no longer exist and detached bow shock-induced combustion or a detached overdriven detonation wave was observed. Introduction Oblique detonation wave (ODW) stabilized over a body was given interests for a last decade, since is it considered as a promising combustion mechanism for novel hypersonic propulsion systems such as a ram accelerator or an oblique detonation wave engine. Classical theory of ODW with Rankine-Hugoniot theory assuming immediate heat addition behind an oblique shock wave was summarized by Pratt[1], and Shepherd[2] summarized recent theoretical and experimental results of ODW for propulsion application. 0 5 10 15 20 25 30 35 40 45 0 15 30 45 60 75 90