Experimental and Numerical Studies on Large-Amplitude-Pitching Double-Delta Wings

In current study, the unsteady loads and flow characteristics of a 75°/50° double-delta wing in large amplitude sinusoidal pitching motion were studied experimentally and numerically, and compared with a 50° sweep nonslender delta wing. The experimental study was conducted in a water channel facility. A wide variety of flow conditions were considered in the present study by systematically varying the reduced frequency (k=0.03~0.48), while keeping the pitching amplitude and the Reynolds number fixed. The hysteresis phenomenon of unsteady force was found in the water channel force measurements. The hysteresis effect increases with the increase of reduced frequency. Compared the 50° delta wing, the hysteresis loop of double-delta wing is smaller at low reduced frequency. As the reduced frequency increases, such difference becomes smaller. In the numerical simulation, the DDES turbulence model was used to simulate the flow field of the pitching double-delta wing. The results of flow field show that the leading-edge vortex on suction surface is the main factor affecting aerodynamic force at low reduced frequencies, and the hysteresis effect of unsteady flow force is mainly related to delayed breakdown of the leading-edge vortices in pitching up and the delayed restoration of the leading-edge vortices in pitching down. At high reduced frequencies, the influence of leading-edge vortices on aerodynamic forces decreases, and the additional circulatory force generated by pitch angular velocity becomes the dominant factor of aerodynamic forces. Therefore, the lift characteristics of delta wing and double-delta wing tend to be the same at high reduced frequencies.