Narrow Results

As combat aircraft becomes more and more maneuverable, the need to understand the unsteady behavior of aircraft in dynamic flow fields becomes more important. Usually researchers pay more attention to the effects on the changes of AOA, but ignore the effects of velocity variations. It is known that the velocity of aircraft changes greatly when the aircraft undergoes a high angle of attack maneuver, like "cobra" maneuver. To completely simulate and study the effect of rapid changes in both free stream velocity and angle of attack, a pitching motion setup is developed in the unsteady wind tunnel of NUAA. By measuring unsteady loads, unsteady pressure distribution and flow visualization, the unsteady aerodynamic behavior of a pitching isolated delta wing and the pitching delta wing coupled with unsteady free stream are investigated. It is found that the oscillating free stream velocity affects the hysteresis characteristics of the pitching delta wing further. The pressure distribution and flow visualization measurements show that the changes in the structure of the leading-edge vortices are the main reason. These studies conclude that a good understanding of the unsteady aerodynamics is vitally important in the design of super-maneuverable aircraft.

In this paper, numerical investigation was conducted for an oscillating NACA0012 foil combining the pitching and plunging motions. The plunging follows a sinusoidal motion while the pitching trajectory is controlled by achieving the resultant effective angle of attack (AOA) to be a harmonic cosine form. Computations were conducted over a range of the Strouhal number (St), different maximum effective AOA and different phase difference between pitching and plunging (ψ). Results show that, at higher St, significant improvement on propulsion performance has been achieved when the effective AOA profile maintains a harmonic cosine form by controlling the pitching motion of the foil.