This thesis provides an in-depth investigation into the development, implementation, and aerodynamic performance of fluidic-oscillator-based pulsed jet actuators for active flow control applications on vertical tail plane configurations. The motivation for this study stems from the need to improve the yaw control authority of vertical tails during critical conditions such as one-engine-inoperative scenarios, thus enabling reductions in stabilizer size, structural weight, and parasitic drag for future aircraft designs. The specific type of pulsed jet actuator was selected for the suppression of flow separation on the vertical tail due to their capability to produce pulsed jet forcing without the need for moving mechanical components, enhancing robustness and scalability. The actuators were designed with an emphasis on achieving a minimum target actuation frequency through internal geometric parameters, including feedback loop length and throttling characteristics. Bench-top experiments were conducted to evaluate the actuators, jet dynamics, switching behavior, and modulation quality. These tests confirmed the ability to reliably generate pulsed jets with high modulation levels and the scalability to match the targeted actuation frequencies for the subsequent vertical tail flow control experiments. During the bench-top investigations, important dependencies between the internal geometry, mass flow rate, and oscillation frequency were identified, enabling the design to be tailored regarding the actuator integration into the vertical tail model. Following the pulsed jet actuator characterization, a modular vertical tail plane model was designed and constructed, incorporating the actuators along both the stabilizer leading edge and the rudder hinge line. Multiple wind tunnel experiments were conducted in the "großer Windkanal" facility at the Technical University of Berlin, utilizing a six-component balance for force and moment measurements, as well as stereoscopic particle image velocimetry to capture detailed flow field structures. The test conditions covered a range of sideslip and rudder deflection angles combined with multiple different flow control settings. The fluidic pulsed jet actuators achieved substantial improvements in the vertical tail plane’s side force coefficient by reducing or completely eliminating the flow separation at the rudder. To assess the relative performance of the pulsed jet actuators, a direct comparison was conducted against sweeping jet actuators under matched momentum input conditions. The results indicated that the actuators with pulsed blowing achieved comparable, and in some cases superior, aerodynamic benefits. However, in certain sideslip and rudder deflection angle setups and with high mass flow rate input, the sweeping jet actuators showed a larger effect. Furthermore, it was identified that the pulsed jet actuators are more effective in the mid span region while the sweeping jet actuators showed larger potential in the vertical tail root and tip region, indicating that a combined solution could be optimal. The findings from this research contribute to the broader field of unsteady active flow control by establishing key design guidelines for designing fluidic-oscillator-based pulsed jet actuators and their implementation in control surfaces. The investigated flow control method presents a viable path toward lighter, more efficient control surfaces by reducing flow separation effects, thus contributing to the broader goals of aerodynamic optimization, fuel savings, and environmental impact reduction in aviation.
Stephan Löffler (Thu,) studied this question.