Effect of the leading edge shape on the formation of asymmetric vortex flow over delta wing of varying sweep angles

A significant loss of lift and increase in rolling moment due to the formation of asymmetric vortex flow can occur on delta winged aircraft and affect the vehicle's stability and control with disastrous consequences. The effect of sharp and round leading edge shapes on the formation of asymmetric vortex flow on double delta wings of varying sweep angles at different Reynolds numbers were, therefore, investigated and the results are presented in this paper. Both surface flow visualisation and surface pressure measurements were employed in the investigation. In order to investigate the effect of round leading edge shape on symmetry breaking, additional efforts were made to locate the primary vortex reattachment line as a function of chord wise location so that they could be compared with sharp leading edged delta wing results. The study found that sharp nose-tip shapes did not generate asymmetric vortex pair even at high angle of attack, whereas the round leading edge delta wings generated significant vortex asymmetry even at moderate angles of attack. Changing the angle of attack and Reynolds number were found to induce laminar and turbulent separation over the round curvature resulting in the production of asymmetric vortices. Also sharp leading edged delta wings created more suction than the round leading edge double delta wings with the same sweep angles. The study also found that the strake and the wing vortices of double delta wings with sharp leading edge merged at a moderate to high angle of attack and maintained flow symmetry, whereas the strake and the wing vortices of round leading edged ones did not. It was, therefore, concluded that the nature of the leading edge shape plays an important role in the generation of asymmetric vortex flow on delta wings.