<p>The decrease in ejector efficiency under off-design conditions poses a significant challenge in ejector design. This study proposes a novel approach incorporating aerodynamic cavities into the mixing chamber of a supersonic ejector to enhance its performance, particularly under high back pressure conditions. A numerical parametric study was performed to determine the cavities’ optimal location, number, depth, maximum width, and opening width. Incorporating the optimized double-pair cavities at the optimal pressure ratio resulted in a 2.55 % increase in the entrainment ratio compared to an ejector without cavities. Additionally, the cavities enabled substantial performance improvements under off-design conditions, allowing the ejector to operate at higher back pressures. Specifically, at pressure ratios of 2.2 and 2.25, the cavities resulted in 50 % and 163 % increases in the entrainment ratio, respectively significantly expanding the operational range of the ejector. The investigation revealed that the cavities induce internal vortices and reduce the secondary flow blockage caused by the mixing chamber walls. These reasons increase the effective cross-sectional area of the secondary flow and decrease the static pressure inside the cavities, collectively enhancing the momentum of the incoming secondary flow and the ejector’s entrainment ratio. This innovative cavity-based passive flow control strategy demonstrates considerable promise in advancing supersonic ejector designs.</p>