Enhancing subsonic ejector performance by incorporating a fluidic oscillator as the primary nozzle: a numerical investigation

Abstract

Primary flow structures affect ejector performance by impacting momentum transfer to the secondary flow and pressure reduction in the suction chamber. This study investigated the potential benefits of oscillating the primary flow in ejectors to enhance the shear-turbulence mixing and momentum exchange between the primary and secondary flows and improve the entrainment ratio. A vortex-based fluidic oscillator was scaled down and designed to serve as the primary nozzle in a two-dimensional subsonic ejector, embedded between the secondary channels. Prior to installation, optimal values for the nozzle exit position and mixing chamber height were obtained through a parametric study and used in the ejector with the oscillator. To evaluate the impact of the fluidic oscillator on the ejector entrainment ratio, unsteady Reynolds-averaged Navier–Stokes equations were solved using the k–ε standard and k–ω shear-stress transport turbulence models in the Fluent 2022 R2 software. The results indicated that a harmonically oscillating primary flow was generated, increasing the mixing entrainment and momentum transfer while reducing the pressure in the suction and mixing chambers. The oscillator improved the ejector's entrainment ratio by 38.3% compared to the baseline, and 11.6% compared to the parametrically optimized ejector. It also expanded the ejector's performance range.

Keywords

• Fluidic oscillator
• velocity fluctuation
• ejector
• secondary mass flow rate
• entrainment ratio
• mixing shear layer