Analytical Predictions of Strong Pseudo-Steady Mach Reflections for the Polyatomic Gas: SF₆

Abstract

Strong pseudo-steady Mach reflections in sulfur hexafluoride (SF 6 ) are analyzed using the three-shock and local three-shock theories, where both the vibrationally-frozen (γ = 1.333) and -equilibrated (γ = 1.093) perfect-gas models are used to compare with existing experiments. The ranges of the incident shock Mach number and reflecting wedge angle studied are 1.49 ≤ M s ≤ 5.95 and 10° ≤ θ ω ≤ 42°, respectively. It is found that predicted angles between the incident and reflected shocks from the local three-shock theory using the vibrationally-equilibrated fictitious perfect-gas model (i.e., γ = 1.093) agree closely with those, currently available in literature, measured experimentally; while these predicted angles obtained using the vibrationally-frozen perfect-gas model (i.e., γ = 1.333) differ significantly from the existing experiments. Taking the convex Mach stem curvature at the triple point into consideration, it is shown that both the triple point trajectory angle and the angle between the incident and reflected shocks of strong pseudo-steady Mach reflections in SF 6 can be more accurately determined for wide ranges of M s and θ ω from the three-shock theory using the vibrationally-equilibrated fictitious perfect-gas model than those without considering this effect.