This helicopter wing flow control device deploys a plasma actuator with a linear counter-flow point embedded electrode design to force airflow around curved surfaces to counter dynamic stalls. Dynamic stalls occur when a wing loses lift at a high pitch rate. These undesirable events limit the maneuverability and maximum velocity of helicopters. Various aircraft components counteract dynamic stall, often by adding momentum to the fluid flowing around the wing. For example, blowing more air into the flow region adds momentum. However, blowing can only drive the air at frequencies up to 500 Hz. Plasma actuators are cutting-edge devices that force airflow by adding momentum with the benefit of being lightweight and operating at frequencies as high as tens of thousands of Hz. Nevertheless, placing plasma actuators on helicopter wings without hindering performance while still forcing air around sharply curved edges is distinctly difficult. Variations of the traditional plasma actuators use large, embedded electrodes that struggle to force air around high curvature surfaces.
Researchers at the University of Florida have developed a plasma actuator design optimized for generating airflow around the leading edges of helicopter wings. By placing the exposed electrode just downstream of the leading edge, the linear counter-flow point embedded electrode design achieves air flow control without undesirable side effects such as passive delay.
High voltage, high-frequency plasma actuator for airflow control to counteract dynamic stall
Plasma actuators convert an alternating voltage signal that can be as much as 50 kHz in frequency into fluid momentum. Plasma is necessary because it contains two types of mobile charged particles, negatively charged electrons and positively charged ions, whereas only the electrons are mobile in most matter. The momentum appears as the voltage alternates in sign, switching the charge carriers. For example, positive voltage may cause negatively charged electrons to transport right to left. The electrons collide with the neutral atoms of the flowing fluid (e.g. the air flowing past the helicopter wing) during this transport, inducing leftward momentum, but this momentum is tiny because the electron mass is tiny. Switching the sign of the voltage to negative would then cause positively charged ions to transport left to right. These also collide, creating rightward momentum that dominates the momentum due to the electrons because ions possess much more mass than electrons do.
With the voltage sign changing many times a second, more and more rightward momentum is quickly added to the fluid. Designing plasma actuators requires different geometries depending on the desired direction of the fluid momentum. For example, in wings the unperturbed fluid flow is roughly parallel to the plane of the wing. The linear counter-flow point embedded electrode shines in giving the fluid momentum against that flow, even around dramatically curved edges such as helicopter wings.