Control of separated flow transition over a highly loaded compressor blade via dynamic surface deformation

Abstract

The laminar separation and transition process seriously deteriorate the aerodynamic performance of a compressor blade at a low Reynolds number (Re). To suppress the laminar separation without reattachment over a highly loaded compressor blade at Re=3.5 × 105, an active flow control strategy based on dynamic surface deformation (DSD) is numerically investigated by large eddy simulations (LESs). The control mechanism of DSD is analyzed, and the vortex dynamics in the transition process are resolved. Furthermore, the loss mechanism is clarified based on the turbulent kinetic energy (TKE) budget analysis. For the uncontrolled case, the rolling-up and breakdown of large-scale hairpin vortices accelerate the generation of turbulent fluctuations, which distinctly extend the region of high-level TKE production term and thus cause large total pressure loss. As the DSD is activated at the oscillation frequency f0 (f0 is the vortex shedding frequency in separated shear layers), periodic pressure fluctuation waves are induced with the appearance of small-scale vortices. The convection of these vortices enlarges the local vorticity and makes the boundary layer velocity profile fuller, which successfully eliminates the large-scale laminar separation on the compressor blade. As such, the region of high-level TKE production term shrinks distinctly due to the weakened vortex dynamics, and the total pressure loss is reduced by 78.9%. With increasing the oscillation frequency from f0 to 2f0 or 4f0, the loss is slightly enlarged due to the rapid growth of turbulent boundary layers, but it is still lower than that of the uncontrolled case. The results demonstrate that DSD is feasible in controlling large-scale laminar separation, and there exists an optimal oscillation frequency.