Oscillatory and transient flow modes in block nozzle arrangements with a base region

Abstract

Multi-jet interactions are characterized by a number of shock and expansion waves, formation of turbulent shear layers and subsonic recirculation zones. The problem of the occurrence of unsteady, transient and oscillatory, processes arising in the nozzle devices of rocket engines at different flight modes is discussed. The main flow regimes, the sequence of their change and qualitative patterns of shock-wave structures that arise in each of the regimes are considered. The main emphasis is paid to the causes of occurrence and mechanisms of maintenance of low-frequency oscillations of the base pressure. The regularities of changes in the amplitude-frequency characteristics of oscillations are studied depending on the main parameters of the problem. Areas of existence of oscillatory processes are found, and a search is carried out for the ranges of design parameters, geometric characteristics of nozzle assemblies that provide a non oscillating flow of gas-dynamic processes. Hysteresis phenomena of shock-wave structure at increase or decrease in the reservoir total pressure is observed.