Abstract: A numer ical investigation of the structure of the vortical flowfield over a delta w ing w hen undergoing aPitch-up motion from 0 to 90 is presented her e. Three-dimensional Navier-Strokes numerical simulations were carried out to predict the complex leeward-side flow field char acterist ics that are dominated by the effect of the breakdown of the leading-edge vort ices. Tw o cases are considered to investig ate the frequency effect on the flow field structure and aer odynamic lo ads for the delta w ing . The later al moments are more evident as the frequency decr eases.Pitching motion w ith hig h frequency delays t he vortex br eakdow n. Besides, the influences of a tr ansient lateral disturbance on the later al aerodynamics are resear ched. For low er fr equency case, the later al moment diverges even ift he disturbance occurs at an angle of attack at which the vortex do not breakdown over the wing . As the frequencyincreases, the lateral moment has no evident chang e after the transient lateral disturbance occurs, and t he lateral-directional stability is more pro nounced.

Key words: aerodynamics, vortex flow, computational method, high angle of attack