Asymmetrical Vortices Breakdown of Delta Wing at High Incidence

A fully implicit LU-SGS with pseudo time sub-iteration and the modified Jameson’s central schemes are applied to solve the thin layer Navier-Stokes (N-S) equations for the high angle of attack (AOA) flows around two delta wings. The asymmetrical vortices breakdown flows with M∞=0.3, Re,cr=1.3×10 6 , and at high AOA around an 80 deg swept delta wing are presented and discussed. To validate the codes for the vortical flows, a comparison is done for transonic cases, where M∞=0.85, α=10 and 20 deg, and Re,cr=5×10 6 , around a 65 deg swept delta wing are demonstrated. The computational results are compared to those in experiment and reference. I. Introduction Modern fighter aircraft demands the improved supermaneuverability to win air superiority. Supermaneuverability is reached when the fighter has both “post-stall” and “direct-force” capabilities. In a post-stall maneuver, the aircraft flies for a short period of time much larger than the maximum lift AOA while the direct force capabilities is “the ability of aircraft to yaw and pitch independently of the flight path”. One of the key technologies for supermaneuverability fighter is the use of a delta wing 1 . Almost all the modern fight aircrafts have indeed wings in a delta shape, or in a combination of strake and delta wing. The characteristic flow pattern of delta wings is the formation of a pair of leading-edge vortices over the upper surface of the wing at some AOA. The vortices are created by the rolling of shear layer that separated at the leading edge and are carried downstream by the longitudinal component of freestream velocity. The rotating flow reattaches to the upper surface and can separate again to form secondary, even tertiary vortices. Between the two primary vortices, the flow attaches to the wing. The two vortices are a source of energy with very high speeds and create a low surface pressure beneath them. It produces an additional lift force called “vortex lift” that increases until high AOA. As the AOA increases, these leading edge vortices experience a sudden disorganization, known as vortex breakdown, which can be described by a rapid deceleration both the axial and swirl components of the mean velocity, at the same time, with a dramatic expansion of vortex cores. The flow undergone breakdown is very chaotic and turbulent. As the position of breakdown moves upstream with an increasing AOA, this ultimately leads to the stall of the delta wing. A large number of experimental, computational and theoretic studies about vortex breakdown continue today. The asymmetrical flows over slender missile body are mainly achieved by adding some very little asymmetric geometry in the experiments 2 and computations 3 . However, relatively few