Wing rock motion induced by forebody asymmetric vortices in pitch-up

Abstract

Aiming to the issue that the angle of attack was usually fixed rather than pitched-up in the previous researches about the wing rock induced by forebody asymmetric vortices,series of wind tunnel experiments were conducted in Beihang University D4 wind tunnel over the configuration of a pointed ogive-cylindrical body with 30° swept wings. Effect of pitch rate on wing rock motion as well as the mechanism of that was first studied through wing rock experiments in different pitch rates. The flow mechanism of wing rock in high rate pitch-up was then studied through the surface pressure measurements during the dynamic wing rock.Experimental results show that,as the wing rock motion time reduces with increase of pitch rate,the motion patterns of wing rock are different in three different intervals of pitch rate. The sinusoidal-like motion,which is totally different from the motion at static angle of attack,would occur in the third interval with high rate pitch-up. The variation of forebody flow with angle of attack,instead of the variation of forebody flow with roll angle,is found to be responsible for the sinusoidal-like motion in high rate pitch-up. Hence,the flow mechanism of wing rock in pitch-up is greatly different from that at static angle of attack.