Experimental Study on the Internal Flow Characteristics for Recess Length in a Swirl Coaxial Injector

Abstract

The objective of this study is to investigate experimentally the internal flow characteristics by recess length of swirl coaxial injector for gas generator has propellant of Kerosene-LOx. The recess length is a very important geometric parameter, has a strong influence on the coaxial spray stability and LOx post damage because it varies the collision position between two liquid propellants. This paper describes the design of swirl coaxial injector to enable flow visualization and film thickness measurement, the results of cold flow tests using simulant fluid. The experiment conducted in eight cases of recess length, liquid film thickness variations after collision between two liquid flow were measured by using the electrical conductance method. Additionally, the experiment for the case of reversed mixing between two liquid flow conducted to investigate the effect of swirling direction. The influence of recess length was analyzed by visualizing internal flow and measuring liquid film thickness and manifold pressure. Also, each spray characteristics by recess length was investigated in internal or external injector. The results of a series of cold flow tests show that the recess length significantly affects the spray cone angle, variation in film thickness, amplitude and frequency of liquid film surface wave. As the degree of internal mixing increases, the frequency of liquid film surface wave increases. However, the wave amplitude showed the different tendency toward mixing direction between two liquid flow. The low frequency fluctuations observed in liquid film are thought to be related to the interaction between both of the temporal and spatial fluctuation of mass flow rate and the internal mixing of liquid film inside confined wall due to LOx post recess.