Experimental investigations on mixing characteristics in the critical regime of a low-area ratio supersonic ejector

Ejectors have many applications in aerospace and energy conversion technologies. An ejector is a passive device that pumps a secondary fluid by energy augmentation from a primary fluid. The performance of the ejector is primarily dependent on the complex gas dynamic interactions between the primary and secondary flows in a variable area duct. The maximum mass flow rate of the ejector in the critical flow regime is limited by choking of both the primary and secondary flows. This paper focuses on experimental investigations on the mixing characteristics of the ejector having an area ratio of 2 in the critical flow regime for a range of stagnation pressure ratios varying between 5.49 and 11.12 and a primary Mach number of 1.5, 2.0, and 2.5. The gas dynamic flow field is visualized using non-invasive high-speed schlieren and Mie-scattering techniques. Mie-scattering images are used to gain insight into the mixing characteristics and estimate the non-mixed length. The optical measurements are complimented with the wall static pressure measurements. The experimental performance data are compared with two well-established analytical models. The characterization of the mixing in the critical operating regime of the ejector using optical tools is being reported here for the first time. An important outcome of the paper is the observation of a significant increment in the non-mixed length to the tune of 55% increase in the critical flow regime in comparison to the mixed flow regime. Published under license by AIP Publishing