Affiliations: Mechanical Engineering, Graduate School, Sunchon
National University, 315 Maegok-dong, Suncheon, Jeonnam 540-742, Korea | Department of Mechanical Engineering, College of
Engineering, Seoul National University of Technology, Gongreung 2-dong,
Nowon-gu, Seoul 139-743, Korea. E-mail: jysung@snut.ac.kr | School of Mechanical and Aerospace Engineering,
College of Engineering, Sunchon National University, 315 Maegok-dong, Suncheon,
Jeonnam 540-742, Korea
Abstract: The three-dimensional vortical structures formed in the wake behind
a road vehicle were measured using a particle image velocimetry (PIV) technique
and the change of the structures by the existence of an air spoiler was
investigated. The measurements were carried out in several x-y, y-z and z-x
planes to obtain full three-dimensional flow fields, including an out-of-plane
velocity component, obtained by interpolating the velocities in the other
plane. Then, the velocity gradient tensor is evaluated to obtain the vortex
core by the λ_2-definition. The relationship between
streamwise, longitudinal and spanwise vortices is systematically analyzed by
overlapping the vortex lines and vortex cores and the whole flow topology is
compared in both cases with and without an air spoiler. As a result, an air
spoiler was found to weaken the C-pillar vortices producing strong wing tip
vortices, which reduce downwash flow and longitudinal vortices increase in the
vertical direction. The recirculation zone formed when an air spoiler is
installed is higher and narrower than without a spoiler.
