Affiliations: Department of Mechanical Engineering, Pohang
University of Science and Technology, San 31, Hyoja-dong, Pohang, 790-784,
Republic of Korea. E-mail: [email protected]
Abstract: The shear layer evolution and turbulent structure of near-wake
behind a sphere at Re=11,000 and 5,300 were investigated using a smoke-wire
visualization method. A laminar flow separation was found to occur near the
equator. The smooth laminar shear layers appeared to be axisymmetrically stable
to the downstream location of about x/d=1.0 at Re=11,000 and x/d=1.7∼1.8
at Re=5,300, respectively. At Re=11,000, the vortex ring-shaped protrusions
were observed with the onset of shear layer instability. Moreover, the
transition from laminar to turbulence in the separated flow region occurred
earlier at the hiher Reynolds number of Re=11,000 than at Re=5,300. The PIV
measurements in the streamwise and cross-sectional planes at Re=11,000 clearly
revealed the turbulent structures of the sphere wake such as recirculating
flow, shear layer instability, vortex roll-up, and small-scale turbulent
eddies.
