Optimization of 2D Slot Injection Geometry for Variable Area Turbine Fluidic Throttling

Abstract Previous experiments demonstrated the effectiveness of using fluidic actuators to throttle the core mass flow through a nozzle guide vane passage. This enables a variable area turbine (VAT) without mechanically moving vanes. The most promising of the fluidic actuators tested was a slot on the suction side of the nozzle guide vane. Using a simple model as a guide, a two-dimensional, RANS, CFD Design of Experiments (DOE) was completed to evaluate the predicted mass flow rate reduction, effectiveness, pressure loss, and exit flow angle for various slot geometries. This DOE was succeeded by the experimental evaluation of seven candidate slot geometries in a small-scale, single nozzle guide vane passage. These candidate slots span the geometric parameters previously described. Experiments showed that when the injection pressure matches the upstream pressure, increasing slot width from 6% to 19% of the geometric throat caused the percentage of primary flow blocked to go from 6.4% to 24.8%. When the slot was pitched from 0° to 60° into the oncoming flow the percentage of primary flow blocked went from 16.0% to 18.2%. Finally, when the slot location was moved away from the computationally determined optimal location the primary flow blocked was reduced. All slot geometries tested had promising effectiveness, generally blocking around twice as much mass flow as they were injecting. Additionally, total pressure loss was seen to strongly correlate with the amount of flow blocked no matter the slot geometry. The trends seen in the simple model and CFD did match the experiments, however CFD appears to have overestimated the performance of the best slot designs.