Affiliations: School of Mechanical Engineering, Pusan National
University, Pusan, 609-735, Korea. | Defense Engineering Department, Tongil Heavy
Industries Co., Ltd., 853-5 Woe-Dong, Changwon 641-020, Korea. | Department of Naval Architecture and Ocean
Engineering, Pusan National University, Pusan 609-735, Korea.
Abstract: Phase averaged velocity fields in the near wake region behind a
square cylinder have been successfully obtained using randomly sampled PIV data
sets. The Reynolds number based on the flow velocity and the model height was
3,900. To identify the phase information, we examined the magnitude of
circulation and the center of peak vorticity. The center of vorticity was
estimated from lowpass filtered vorticity contours adopting a sub-pixel
searching algorithm. Due to the sinusoidal nature of circulation which is
closely related to the instantaneous vorticity, the location of peak vorticity
fits well with a sine curve of the circulation magnitude. Conditionally
averaged velocity fields represent the Karman Vortex shedding phenomenon quite
successfully within ± 5° phase uncertainty. The oscillating nature
of the separated shear layers and the separation bubble at the upper and lower
surfaces are clearly observed. With the hot-wire measurement of Strouhal
frequency, we found that the convection velocity changes its magnitude very
rapidly from 25 to 75 percent of the free stream velocity along the streamwise
direction when the flow passes the recirculation region.
