Comparative Numerical and Experimental Studies of Flow Energy Extraction from Controlled Viscous Limit-Cycle Oscillations in Modified Glauert Airfoil

Résumé

The paper addresses development of a novel robust, variable-fidelity, nonlinear flow control technology that employs an array of synthetic-jet micro-actuators (SJMAs) in 2-DOF, elastically mounted, optimized airfoil design with control of limit cycle oscillations (LCO) at low subsonic flow regimes. Such technology is developed for dual-use application. For unmanned aircraft, the use of SJMAs eliminates moving parts (such as ailerons) thus greatly enhancing maneuverability required, e.g., for small fixed-wing air vehicles operating in tight urban environments. Estimated fast response times are critical in mitigating gust-induced aeroelastic effects (such as LCO) while greatly improving flight stability and control. For a conceptual design of the wind energy harvesting system that employs, e.g., a piezoelectric device to extract energy from the plunging LCO, the robust controller is capable of sustaining required LCO amplitudes over a wide range of wind speeds. The new controller design is particularly advantageous for high levels of uncertainty and nonlinearity present both in the unsteady upstream flow environment and in the embedded actuator’s response. Minimal knowledge of the structure of the SJMA dynamic model is exploited, with matrix decomposition technique utilized along with innovative algebraic manipulation in the control development to compensate for the dynamic uncertainty in the SJMAs. The current work reports on the progress in the concurrent numerical and experimental efforts focused on the successful implementation of the controlled LCO technology using the Modified Glauert (MG) airfoil design developed to enable sustained plunging LCO at low upstream flow velocities.