Distributed Mechanical Actuators for Design of a Closed-Loop Flow-Control System

Abstract

Active flow control experiments were conducted on a two-dimensional, single-element NACA 4312 airfoil to assess the performance of vortex generators and gurney flaps as lift-enhancing devices for the control of longitudinal dynamics of an air vehicle. The effort is aimed at creating a database of flow-induced effects for the design of a modular feedback control system to be used on an air vehicle technology demonstrator. Lift and drag forces are measured to quantify the effect of flow-control as a function of several actuator parameters. The vortex-generators are shown to delay boundary layer separation and provide an increase in the lift coefficient for angles of attack above 12 deg, and the gurney flaps yield a constant shift in the lift curve for all angles of attack up to stall angle. The vortex-generators are most effective when used between 2 to 5% chord, and the gurney flap is most effective when used at the trailing-edge. Experiments from actuators distributed spanwise along the wing reveal that there is minimal interaction between individual gurney flaps at low-to-moderate angles of attack, while, the interactions between the individual vortex-generators are slightly more pronounced at high angles of attack. The effects of these individual actuators can be combined linearly to produce a desired net effect. A flow-control system employing both leading-edge vortex generators and trailing-edge gurney flaps can produce significant control authority over an extended flight envelope for maneuvering air vehicles without the use of conventional control surfaces.