Closed-Loop Stall Control using Pulsed-DBD Plasma Actuation

Abstract

A closed-loop stall control system, employing pulsed-DBD plasma actuators, was implemented on the semi-span wing of a 6:1 scale general aviation aircraft model, and evaluated in a wind tunnel. Sensing of incipient stall was achieved by means of pressure ports located just below the leading-edge, inspired by conventional scoop-type pneumatic stall-warning systems. While negative pressure at the scoop orifice draws air though the reed of a horn, to warn the pilot of incipient stall, the present system relies on the pressure zero-crossings to either initiate or terminate plasma pulsations. Decreasing- or increasing-pressure zero-crossings, corresponding to pitch-up or pitch-down, either initiated or terminated pulsations, respectively. Lift and drag coefficient results, based on closed-loop control, were compared with open loop (continuous) plasma pulsations under static and dynamic―harmonic and pitch-and-hold―angle-of-attack variations. Under all light, moderate and deep stall scenarios, at a wide range of reduced frequencies, negligible differences were observed between open- and closed-loop control, thereby demonstrating the viability of the closed-loop system. With increasing pitchrate, the angles-of-attack corresponding to pitch-down zero-crossings increased successively, to angles greater than the static stall angle. This had no measurable effect on the results because the timescales governing boundary layer separation were at least an order-of-magnitude larger than the time-intervals between the zero-crossing angle and the static stall angle. DBD plasma actuators can easily be retrofitted to general aviation aircraft, that incorporate scoop-type stall warning systems, and the next step should be to evaluate the system on a full-scale wing, or in flight.