When supersonic flow is decelerated to subsonic speeds using a series of shock waves, the type of shock waves involved are oblique shocks. During this process, the flow is redirected by the presence of wedges or ramps, leading to a change in flow direction across each shock wave. As the flow passes through these waves, its Mach number decreases progressively.
The key to understanding the variation in shock angles lies in the relationship between the Mach number and the shock wave angle. The oblique shock wave angle (θ) is related to the upstream Mach number (M) and the wedge angle (δ) through the oblique shock wave equations. As the Mach number decreases across each successive shock wave, the requirement for a larger deflection angle (δ) leads to an increase in the shock wave angle (θ).
Therefore, as the series of shock waves progresses from supersonic to subsonic speeds, the half angle of the shock waves increases. This can be visualized as the shock waves being less angled initially and becoming more angled as the flow's Mach number reduces.
Correct Answer: Increasing half angle from the first to last.
