Experimental Investigation of an Annular Injection Supersonic Ejector
E JECTORS have a wide variety of applications: thrust augmentation of jet engines, vacuuming systems, and thermocompressor of the desalination plant, to name a few [1–7]. Depending on the applications, different configurations of ejectors have been in use. Interestingly, however, most of the past works on ejectors reported central injection ejectors, where primary flow is injected along the centerline of the secondaryflow.When ejectors are used for pumping chemical lasers, central injection type ejectors cannot be used because the passage of primary flow is exposed to the secondary flow of hot burnt gas with temperatures well beyond 1200 K [8,9]. By injecting the primary flow annularly, direct contact between the hot secondary flow and primary flow passage can be avoided.Annular injection of the primaryflow is also used in a rocket based combined cycle engine, where the high-momentum of the secondary flow can be maintained by removing the protrusion of the primary flow passage [10,11]. As the annular injection ejectors make up an important part of the systems described above, the study of the annular injection ejectors have been device specific, which can explain the lack of the literature on ejectors with this injection arrangement. In the present study, we investigated the effect of shape of the primary nozzle and configuration of the flow passage downstream of the primary nozzle exit on the performances of an isolated annular injection ejector, namely, static pressure of the secondary pressure and the primary stagnation pressure at the starting and unstarting conditions. By doing so, we intend to understand the performance characteristics and provide a baseline data for ejector sizing. Figure 1 is a typical performance curve of an annular injection supersonic ejector. The normalized primary stagnation pressure was plotted against the normalized secondary pressure. As the stagnation pressure of the primary flow increases, the forepart of the diverging section of the primary nozzle becomes supersonic and the aftpart becomes subsonic with a normal shock demarcating these two flow regions. As a result, subsonicmixing occurs between the primary and secondary flows in the entire mixing chamber. This condition corresponds to region (1) in Fig. 1. As the stagnation pressure of the primary flow increases further, the shock wave is pushed outside of the primary nozzle. Therefore, supersonic mixing takes place in part of the mixing chamber as shown in region (2). When the primary stagnation pressure increases beyond the starting pressure in region (3), the whole mixing chamber is filled with supersonic primary flow, and the shock is swallowed by the second throat. At this condition, the design static pressure of the secondary flow is