Fluid Machinery either extract energy from the fluid (e.g., turbines) or exert energy onto them (e.g., fans, wings). Flow separation over the power extracting/exerting surfaces of such machinery is typically associated with significant loss of lift/thrust/power, increase in drag, increase in fuel consumption, etc. Consequently, there is a great interest in controlling flow separation over these surfaces, which is referred to as flow control, to increase the efficiency of fluid machinery. To overcome flow separation, the flow near the surface needs to be energized. Here, the flow is energized through triggering instabilities by a new lightweight, energy-efficient actuator that generates traveling wave, which is hypothesized to work better than currently available actuators. Therefore, the main goal of this project is to test this hypothesis and optimize the performance of this actuator by gaining a deep understanding of the key parameters that govern the interaction of the actuator with the flow. For example, using the proposed method could reduce fuel consumption of aircraft and, in the meanwhile, allow large aircraft to take off from shorter runways.  This project also embraces significant educational activities, including creation of educational videos and engagement of a diverse group of undergraduate students through well-established programs at our institutions.

The main hypothesis driving this project is that traveling wave actuators perform better than the actuators that create standing waves because: 1) traveling waves also inject momentum (generate thrust), and 2) apart from frequency, an additional parameter (wavelength) can also be tuned to affect flow separation as shown by the preliminary results. The main objective of this work is to test this hypothesis by a complementary numerical and experimental approach on a typical airfoil (NACA0018). Large-eddy simulations (LES) with moving boundaries will provide possible traveling waves for the initial design of traveling wave actuators and elucidate the mechanisms of flow reattachment. The experiments in the wind tunnel, in turn, will provide the data to validate the simulations and test the hypothesis by comparing the traveling against standing wave actuators.