Adjoint optimization of a supersonic ejector for under-expanded, isentropic, and over-expanded primary flow modes

Abstract

The geometric shape of an ejector’s walls plays an important role in the efficiency of the ejector. Depending on the outlet-to-throat area ratio of the primary nozzle, the flow exiting the primary nozzle of a supersonic ejector is categorized as under-expanded, isentropic, or over-expanded. Due to differences in the flow structures exiting the primary nozzle, the optimal shapes of the mixing chamber and secondary channel walls differ for these three flow modes. In this study, the geometric shape of a supersonic ejector was optimized numerically for these three modes. First, various geometric parameters were fixed, and the mixing chamber height was varied parametrically for different area ratios of the divergent part of the primary nozzle to determine the optimal mixing chamber height for the different supersonic flow modes. Then, the wall profiles of different components were optimized numerically for the parametrically optimized ejectors. The adjoint equations in the Ansys Fluent 2022 R2 software were solved, and the cost function was evaluated using a Reynolds-averaged Navier–Stokes flow solver with the k–ω shear-stress transport turbulence model. The results demonstrated that the entrainment ratio of the adjoint-optimized ejectors was 20.8%, 15.3%, and 16.5% higher than that of the corresponding parametrically optimized ejectors for the under-expanded, isentropic, and over-expanded modes, respectively. In addition, the adjoint-optimized ejector exhibited a wider performance range in the under-expanded mode than in the other modes.