Assessing the Impact of ESTS Lobed Nozzles on Ejectors: Performance Gains and Geometric Modification Requirements

Abstract A detailed experimental investigation was carried out to evaluate the effect of elliptical sharp-tipped shallow (ESTS) lobed nozzles on ejector performance. The study included seven nozzle configurations: a baseline conical nozzle and six ESTS lobed variants, all identical up to the throat but differing in the number of lobes in the diverging section. Tests were conducted under consistent conditions with a primary stagnation pressure of 4 bar (gauge). To assess their integration into practical systems, the impact of mixing duct geometry was also examined, with variations in duct length aimed at achieving more compact ejector designs without compromising performance. Performance was evaluated using wall pressure measurements and secondary mass flow rates. The results revealed that lobed nozzles significantly improved mixing efficiency, with one configuration (E3) achieving up to 33% higher efficiency compared to the conical baseline. Furthermore, by optimizing the mixing duct length to match the higher mixing rate enabled by lobed nozzles, the overall ejector length was reduced by as much as 91%, demonstrating their potential in compact system applications. Importantly, the study underscores the need to redesign the mixing duct when adopting lobed nozzles. Without appropriate geometric modification, enhanced mixing causes the flow to experience frictional losses in the remaining duct length, leading to reduced compression performance. These findings highlight that while lobed nozzles offer substantial benefits, they must be integrated with tailored mixing duct geometries to realize their full performance potential.