Experimental and Numerical Investigation of Delta Wing Flutter in Low Subsonic Flow

The problem of low subsonic delta-wing flutter has been studied experimentally and numerically. The wing model is a cantilevered delta wing with a sweep angle of 45˚. In the experiment, the wing starts to oscillate with relatively small amplitude at a particular velocity and then makes rapid transition to an oscillation with higher amplitude at a higher velocity. In the case that an angle of attack is not zero, the delta wing undergoes a static deflection. Effects of angle of attack and the static deflection on the flutter were investigated in detail. As an angle of attack increases, the flutter velocity and the velocity that causes the transition become higher. The oscillation characteristics are also significantly affected by angle of attack. Especially, in the cases with the angle of attack greater than 3˚, there are four regions with different characteristics. They are (a) static deflection, (b) LCO with low amplitude, (c) chaotic vibration, and (d) LCO with higher amplitude. In addition, in order to make sure of the flutter velocity, a CFD and CSD coupling approach was employed. The computed flutter velocity agreed with the velocity obtained in the experiment. Therefore, it is found that the transition at the higher velocity is not typical flutter and exists only when the wing oscillates with high amplitude.