Acoustic and Photographic Studies of Solid Rocket-Propellant Combustion Instability

Abstract

Solid-propellant combustion-instability studies at the Ballistic Research Laboratories have been concerned with three main areas: namely, (1) a photographic investigation of aluminum-additive burning phenomena, (2) acoustic admittance measurements of the burning surface, and (3) measurement of acoustic erosivity effects on the burning rate. The first program, which was recently completed, was a photographic study of possible aluminum-additive contributions to low-frequency instability. In this investigation, propellant slabs were burned in a windowed and vented chamber. A rotating slotted wheel was pulled over the vent in some instances to provide pressure waves normal to the burning surface. A short film is shown of some of the test runs. The second program is concerned with the measurement of the acoustic admittance of a burning-propellant surface, using a resonant-tube technique. This work closely parallels that at the Naval Ordnance Test Station and the University of Utah. Recent studies have been aimed at evaluating experimentally some of the sources of acoustic losses in this system. The third program is a study of the dependence of the burning rate of a propellant on the frequency and magnitude of the fluctuating gas velocity parallel to the transpiring surface. A description of the apparatus and a summary of recent results are given.