Unsteady fluidic oscillators for active controlling boundary layer separation in an ultra-high-lift low-pressure turbine

Abstract

This study used large eddy simulation (LES) to investigate the control mechanism of a fluidic oscillator in the suppression of non-reattachment separation of a boundary layer from an ultra-high-lift, aft-loaded, low-pressure turbine under low Reynolds number. The internal flow characteristics of the fluidic oscillator were examined, with a focus on the influence mechanism of the pulse jet from the fluidic oscillator on boundary layer separation and transition. The effects of different jet angles (θ) on the suppression of separation bubbles were also compared in detail. Finally, the mechanism of interaction between the fluidic oscillator jet and the blade suction surface boundary layer was assessed. It was found that the pulse jet of the fluidic oscillator generated a streamwise vortex pair above the surface of the blade suction, which promoted an exchange of momentum between the boundary layer for the blade suction surface and the main flow, and clearly suppressed boundary layer separation. The streamwise vortex pair at θ=30° showed the characteristics of higher strength, smaller size, slower decay, and longer penetration distance than the results at θ=90°, such that the momentum exchange between the low-energy fluid inside the boundary layer and the main flow is sustainable, which promoted the laminar boundary layer to produce bypass transition and significantly improved the aerodynamic performance of the turbine.