Shock Patterns in the Plume of Overexpanded Rocket

Abstract

The plumes of ideal plane and axisymmetric nozzles as well as the plumes of existing rocket engines are investigated. For ideal plane nozzles, different types of plumes are possible for a full-flowing, overexpanded nozzle: A regulr shock reflection at the axis, a Mach disk and a single curved or straight shock at the exit. For these nozzles, the occuring shock pattern is given as a function of the corresponding exit Mach number and pressure ratio, merely by using the oblique shock relations and the conditions for Mach reflection. Similarities and differences to the ideal axisymmetric nozzle are presented, some experimental data are used for comparison. In rocket engines with thrust.optimized nozzles, another stable shock pattern can exist, the cap shock with its trapped vortex. This pattern is analyzed in detail, and the transition process to a Mach disk is investigated using medium speed motion pictures.