Triple shock configurations with negative angle of reflection

• New pattern of the triple-shock configuration is studied.
• Reflected shock is inclined downwards the initial flow direction.
• Instability of this configuration leads to a radical change of flow pattern.
• This instability influences the Mach reflection at small specific heats ratios.

A triple configuration of stationary shocks in a steady gas flow is studied analytically. The study reveals that a new pattern of the triple-shock configuration is formed within the range of Mach numbers exceeding 3.0 and specific heat ratios below 1.4. The reflected wave coming from the triple point deviates down and forms a negative angle of reflection with the initial flow direction. This shock-wave pattern differs from the known positive reflection angle configuration where the reflected wave is inclined upwards to the initial flow direction. The negative angle configuration effect is considered in this study in the problem of a supersonic flow about two wedges. It has been shown, that this configuration is unstable and its appearance leads to a radical change of the total flow pattern. It is suggested that this effect can cause an evident alteration of the flow wave pattern in the problem of a supersonic jet nozzle structure.The range of flow parameters in this study (large Mach numbers and small ratios of gas specific heats) corresponds to spacecraft flights (for example, in Mars atmosphere), as well as flows from the rocket nozzles with triple configurations at Mach reflections in both overexpanded and underexpanded jets. Instability supersonic flows with the analyzed triple configurations can influence both the aerodynamics of spacecraft flight and the functioning of its propulsion engine.