Control of Separation for Turbulent Boundary Layers Subjected to Wall Curvature and Streamwise Pressure Gradients

摘要

Low Pressure Turbine (LPT) stages are important for modern jet engines, and in particular for engines used in Unmanned Aerial Vehicles (UAV). At low operating Reynolds numbers boundary layers remain laminar over a large downstream extent of LPT blades. Laminar boundary layer separation can cause significant reductions in turbine and overall engine performance. In an experimental research program at the Air Force Research Laboratory (AFRL), the potential advantages of Active Flow Control (AFC) for separation control were systematically explored. In collaboration with the experimental effort, we performed numerical investigations of AFC for LPT separation to investigate the relevant physical mechanisms. Numerical simulations can provide insight into flow details that is not possible in experiments. We chose a two-pronged approach: A computationally less efficient but more versatile finite volume code was employed for simulations of the full geometry. Open-loop control strategies were explored in 2-D calculations. Detailed investigations of the VGJ actuation for a flat plate model problem were performed with a very efficient finite difference code. The high-resolution DNS helped identify some of the key physical mechanisms responsible for the effectiveness of VGJs.