| Uninhabited air vehicles (UAVs) are commonly designed with high-aspect ratio wings, which can be susceptible to significant aeroelastic vibrations. These modes can result in a loss of control or structural failure, and new techniques are necessary to alleviate them. A multidisciplinary effort at Stanford developed a distributed flow control method that used small trailing-edge actuators to alter the aerodynamic loads at specific spanwise locations along an airplane wing. This involved design and production of the actuators, computational and experimental study of their characteristics, and application to a flexible wing. This project focused on the experimental response.; The actuators were based on a Gurney flap, which is a trailing-edge flap of small size and large deflection, typically about 2% of the chord and 90 degrees, respectively. Because of the large deflection, there is a significant change to the wing camber, increasing the lift. However, due to the small size, the drag does not increase substantially, and the performance is actually improved for high lift conditions. For this project, a 1.5% flap was divided into small span segments (5.2% of the chord), each individually controllable. These devices are termed microflaps or Micro Trailing-edge Effectors (MiTEs). The aerodynamic response was examined to determine the effects of small flap span, the influence of the device structure, and the transient response to relatively rapid MiTE actuation. Measurements included integrated loads, pressure profiles, wake surveys, and near-wake studies using particle image velocimetry.; The basic response was similar to a Gurney flap, as full-span actuation of the devices produced a lift increment of about +0.25 when applied towards the pressure surface. For partial actuated spans, the load increment was approximately linear with the actuated span, regardless of configuration. The primary effects occurred within two device spans, indicating that most of the load was locally applied. The transient response was quasi-steady for dimensionless actuation times (tU/c) near unity. A shorter dimensionless actuation time of 0.2 produced a transient response with significant overshoot of the downwash velocity in the near-wake. This indicated a non-monotonic response of the aerodynamic loads for rapid actuation. |
