Abstract
This dissertation is to investigate the mechanism of flow separation mitigation by co-flow jet (CFJ) active flow control, its energy expenditure, and its micro-compressor actuators to achieve high power conversion efficiency (PCE).
The separation control mechanism of CFJ is investigated by analyzing 2D differential and integral wall jet momentum equations. The CFJ working mechanism includes three factors to offset adverse pressure gradients (APG): 1) The spanwise vorticity established at the wall by the injection and suction is essential to enhance turbulent diffusion and the wall vorticity flux via the suction. 2) The streamwise mass flux provided by the wall jet enhances the streamwise inertia force. 3) APG enhances the streamwise inertia force and turbulent diffusion, which offset the APG itself. CFJ has a mechanism to grow its control capability with the increasing APG. The widely used NASA hump is numerically simulated and validated to support the theoretical analysis, which indicates that turbulent diffusion plays the dominant role to offset the APG. The energy expenditure of CFJ is numerically studied using the NASA hump. A trade study of CFJ injection and suction locations is conducted to fully attach the flow with the minimum energy consumption. As the application of separation control mechanism study, CFJ is applied on an aircraft control surface, an engine serpentine inlet and a 3D wind turbine blade. Significant performance improvement with high energy efficiency is achieved for these applications.
As the effort to increase PCE, a high specific speed mixed flow micro-compressor CFJ actuator is designed to achieve high efficiency and high torque density. To further enlarge the operating range of the micro-compressor, the axial groove (AG) and recirculating casing treatment (RCT) are studied with various geometrical parameters. Both RCT and AG casing treatments are very effective to enhance the micro-compressor operating range, and AG is preferable due to its simplicity for manufacturing.