This is a review paper of unsteady aerodynamics of a 45°delta wing in rolling motion, based on experimental data collected from the wind tunnel testing at Nagoya University. This wing shows self-induced oscillations at high angles of attack, which seem to be different from those of conventional slender wing rock. The flow physics of this oscillation can be made clear from results of free-to-roll testing for various values of pitch angle. Furthermore, the static rolling moment shows highly nonlinear characteristics with regard to roll angle, which is associated with asymmetric behavior of a pair of leading-edge vortices. Due to this nonlinear change of rolling motion, there occurs a hysteresis of rolling moment.
This paper reviews the study of unsteady aerodynamic characteristics of delta wings at high angles of attack. Experimental Investigations were carried out for slender delta wing models, which were forced to oscillate in roll, in a wind tunnel. Compared with that of the free-to-roll oscillation, the experiment of the force-to-roll oscillation gave a better understanding about unsteady roll characteristics through large range of test parameter (roll frequency, amplitude). The results showed that unsteady rolling moment were influenced by three factors, the roll damping effect and convective time lag of the leading edge separated vortex and temporal delay of vortex breakdown. Finally, unsteady rolling moments were discussed in relation to the wing rock.
Dynamic characteristics of a delta wing in pitching motion near ground as well as in an air were investigated experimentally. Its flight attitude can be changed smoothly and periodically by a robot with six degrees of freedom which is controlled by a microcomputer. A ring-shaped force balance to measure lift, drag and pitching moment was also developed in the research, and it could get force and moment within the error of 1. 6%. It is found that the existence of the ground causes a faster stall and increases the maximum lift coefficient over 5. 6% compared with the result out of ground effect. Coefficients of lift, drag and pitching moment plot a 8-shaped hysteresis loop owing to the time lag of leading edge vortex formation. This hysteresis becomes remarkable at such region of high angle of attack as a stall with an ground effect. Derivative of measured pitching moment coefficients with respect to an attack angle indicates that longitudinal static stability increases in the case of ground effect.
The supersonic transports often have a delta or delta-like wing for the main wing. It is well known that there is a room for improvement, the lift to drag ratio of delta or delta-like wing at a take-off and landing condition could be made better. The leading-edge vortex flap can improve the lift to drag ratio of the wing by forming a leading-edge vortex on the flap. But it is not so easy to form a leading-edge vortex on the full span type vortex flap from the root to the tip. The segmented vortex flap is one of a concept to catch it through the whole flap. The low speed wind tunnel test was held to evaluate the segmented vortex flap's performance.
Low speed wind tunnel measurements were done on 50°and 60°delta wings with rounded leading-edge vortexflaps in order to assess the benefits of the rounded leading-edge vortex flaps. Deflecting the rounded leading-edge vortexflaps improves the lift/ drag ratio at relatively higher lift coefficients, when compared with the sharp edged vortex flaps.