A Simplified Injection Model for Variable Area Turbine Fluidic Throttling

Abstract

Previous studies have demonstrated the effectiveness of using fluidic actuators to throttle the flow through a nozzle guide vane, enabling a variable area turbine (VAT) with no moving parts. A simplified model was developed to assess the driving design factors that influence the blocked flow fraction and throttling effectiveness of the actuators. The model approximates slot injection using a simplified stream tube analysis, neglecting mixing with the primary passage flow. Throttling performance is predicted for fluidic actuators with different widths, orientations, streamwise locations, and pressure ratios. This simplified model evaluates these actuators in a constant width straight duct and a variable width duct. Two-dimensional CFD of injection in the nozzle guide vane passage reported strong agreement with the results of the simple model using the variable width duct. Higher injection pressure ratios result in more injected mass flow but not significantly higher throttling effectiveness. Wider slots retain the effectiveness and block much more primary flow. Upstream oriented injection proves best for both effectiveness and blockage capabilities. Finally, there is an optimal injection location relative to the passage throat, which is extracted by both the model and CFD. This model has potential application for optimizing fluidic VAT throttling designs while saving on the cost of high-fidelity testing and production of these configurations.