Investigation of wing rock on delta wing part 1 : flow field and hydrodynamic force analysis

Abstract

All modern fighter jets incorporate the use of the delta wing in the aircraft design to reduce wave drag and enhance flight performance at supersonic speeds. Delta wings are capable of providing increased lift compared to conventional airfoils due to the suction force generated by the leading edge vortices. However, at high angles of attack, delta wings are also prone to a phenomenon known as wing rock which can occur at high angles of attack and subsonic speeds. This final year project focuses on the study of wing rock of delta wings at high angles of attack in a water tunnel. In the experiment, the hydrodynamic force generated by the delta wing is measured using a force-moment transducer, and the flow visualization is carried out with a dye probe, video camera and a digital SLR. Four delta wings, one Free To Roll device (FTR) and numerous angled joints were designed specifically for this experiment. Special attention was dedicated to the FTR device such that it only allowed movement around the longitudinal axis of the delta wing, and that special water-proof bearings were used to withstand the testing conditions. Experimental data suggests that the wing rock motion is dependent on asymmetrical vortex breakdown over the wing. Discrepancies with other studies could be due to different friction used between systems, which can have a significant on the propagation of wing rock. The conclusion from this study is that there is good correlation between angle of attack, delta wing sweep angle, Reynolds number and the vortex breakdown behavior. In addition, dye flow visualization results show that the asymmetric vortex breakdown occurs at certain conditions.