Near-field/far-field study of the end-effects regime produced by large area ratio nozzles

Abstract

Vibro-acoustic loads emanating from large area ratio rocket nozzles during start-up can be catastrophic to the launch system and payload. This study quantifies a particular feature referred to as the “end-effects regime”, which is considered the largest source of vibro-acoustic loading during start-up [Nave and Coffey, AIAA Paper 1973-1284]. In this experiment, data acquired during the start-up sequence of several full-scale rocket engines are compared to the laboratory-scale measurements of a thrust-optimized parabolic-contour nozzle conducted in a fully anechoic chamber. The laboratory studies encompass both static and dynamic wall pressures measured inside the nozzle, as well as far-field acoustic surveys. The event produced during the “end-effects regime” was successfully reproduced in the sub-scale model, and was characterized in terms of its mean, variance, and skewness, as well as the spectral properties of the signal obtained by way of time-frequency analyses. The intensity and characteristic frequency of the event of interest are discussed through a comparison of the nominal values for the full-scale and sub-scale system and whether they obey with standard scaling laws.