Numerical Study on Large-Amplitude Limit Cycle Oscillation of Delta Wing

We investigate postflutter limit cycle oscillations (LCO) in this study. First, wind tunnel experiments were performed for a cantilevered delta wing model with a sweep angle of 45˚ at low speeds. We found new phenomena in the experiment, such as an existence of small- and large-amplitude modes, a transition between the two modes, a hysteresis loop, and a separation during the large-amplitude oscillation. Next, we investigated these phenomena using a CFD-CSD coupled method. A nonlinear structural model is used for the delta wing. The computed flutter velocity is in good agreement with the measurement. The largeamplitude limit cycle oscillations were computed for angles of attack of 0° and 2°. The computation with the structural damping shows a good agreement with the experimental data including the small- and large-amplitude modes. It was found that the structural damping is important to simulate the large-amplitude LCO. In addition, the large separated vortex is produced continuously due to the twisting motion during the LCO, and it makes large aerodynamic forces on the wing.