Lift and L/D Enhancement in Vortex-Shedding Flows Using Predictive Cost Adaptive Control

This paper applies feedback control to improve the performance of an airfoil using two different actuators. In the first case, feedback control is applied to an airfoil that can deform over a small width. The goal is to enhance the time-averaged lift of the airfoil by modulating the deformable portion of the airfoil. Two examples are considered for this control mechanism. First, an estimate of the instantaneous airfoil lift is assumed to be available. Second, a pressure measurement at a fixed location is used. Because of the vortex shedding, both the controlled and uncontrolled cases display an oscillatory lift signal, and thus the goal is to improve the time-averaged lift relative to the open-loop, time-averaged lift. In the second case, feedback control is used to modulate a blowing jet placed upstream of the separation point on a stalled NACA 4412 airfoil. Here, the lift-to-drag ratio is used as the measurement, and the feedback controller is tasked with improving the lift-to-drag ratio relative to an uncontrolled case. The feedback controller used in the numerical experiments is called predictive cost adaptive control (PCAC), and it combines online closed-loop system identification with model predictive control. PCAC is implemented as a cold-start controller, and thus requires no prior data or model. In the first case, numerical results demonstrate the ability of PCAC to enhance the time-averaged lift of the airfoil by modifying the surface pressure of the shed vortices, with the closed-loop, time-averaged lift following the commanded lift setpoint. In the second case, PCAC successfully tracks a commanded time-averaged lift-to-drag ratio, improving the efficiency of the airfoil.