An investigation of the effect of a tangential gas velocity on combustion instability.

Abstract

A small, uncooled research rocket motor was built to study the effects of a vortex flow on combustion instability. Normal heptane and air were used as propellants with the air being divided into two flows; a primary flow at the center of the combustion chamber and a secondary flow at the periphery of the chamber. The secondary air provided the swirl which could be directed clockwise or counterclockwise at various angles or a straight mode of operation. Runs were made at various flow rates with the direction of swirl changed during the run. A first tangential high frequency mode of combustion instability was developed and a significant change in stability conditions was found when a vortex flow was generated within the combustion chamber. It was found that a swirl in one direction tended to decrease the instability while a flow in the opposite direction increased it.