Boundary Layer Control With Low-Pitch Spanwise-Swept Wall Injectors

Jets in crossflow (JICF) have been a primary focus for fluid dynamics studies for decades, and have been seen in applications including turbine blade film cooling and mixing for combustion systems. These systems typically focus on the physics in the near-field of the injector. More recently, studies have investigated the use of JICF for active boundary layer control which focus on the interaction of the issuing vortex with the high momentum crossflow and the low momentum boundary layer flow. This work investigates the effect of a shallow-inclined and swept fluidic injector on a canonical flat plate boundary layer. The injector, which is encased in a mound to achieve an extremely shallow incline, is assessed in terms of its ability to modify the boundary layer parameters through the introduction of near-wall vorticity, particularly focusing on improvements in boundary layer thickness (δ99), displacement thickness (δ^*), and momentum thickness (θ). A series of single jet configurations are investigated, which include variations of the Nozzle Pressure Ratio (NPR), pitch (α) and skew (β) of the jet. Results indicate up to 50% reductions in boundary layer height and improved flow characteristics, particularly at lower NPR values, indicating a low energy requirement for such improvements. Improvements also favored the larger β values due to superior spanwise penetration of the crossflow by the injector. The low momentum fluid from the boundary layer is effectively transported from the target region using shallow-inclined and swept fluidic injection, notably in the far-field for the case of the wind tunnel wall boundary layer (Djet/δ99 = 0.10).