Numerical Simulation of Full-Span Delta Wing Buffet at High Angle of Attack

Abstract

In this work, the buffet of a full-span, highly flexible, 50-deg-sweep delta wing at high angle of attack is studied using a computational aeroelastic solver. The aeroelastic solver couples a second-order finite difference solution of the Euler equations to a large-rotation nonlinear finite element structural solver. Particular attention is paid to the poststall region, in which previous experiments on highly flexible low-sweep delta wings have noted increased buffet response accompanied by lift enhancement and a delay in stall. It is thought that these phenomena are due to the reorganization of the flow and reformation of a leading-edge vortex structure. The nature of this enhanced lift is studied here for the flexible delta wing at an angle of attack of 25 deg and a flow velocity of 30 m/s. Using a prescribed wing motion, it is shown that it is possible to predict lift enhancement by solving only the inviscid Euler equations. The enhanced lift is due to a reorganization of the flow and the resulting region of increased suction near the apex of the wing. It is found that the mode of wing vibration has little influence on the enhanced lift phenomena, because both a prescribed symmetric first-mode motion and a prescribed antisymmetric third-mode motion led to lift enhancement. It is also insensitive to the wing vibration frequency for the range of frequencies tested, with the concession that below some minimum frequency, lift enhancement does not occur. The amplitude of wing vibration has some effect on the time-averaged lift coefficient. Fully coupled aeroelastic computations were also performed in this study for the wing. The fully aeroelastic computation did not predict the enhanced structural dynamic behavior and lift that was observed in the experiment. The dominant dynamic response of the wing was near the first mode, which has a frequency that is too low to initiate flow organization and the resulting enhanced lift due to increased suction.