抄録
The flow characteristics of unsteady flow through a symmetrical sudden expansion were investigated experimentally using digital particle image velocimetry (PIV). Expansion ratio (downstream to upstream area ratio) of 4 and 2 were selected comparatively for the study. The instantaneous two dimensional velocity profile and flow resistance were obtained. The results of pulsatile flow were compared with those of steady flow with the Reynolds number ranged from 300 to 7500, based on the upstream hydraulic diameter (De). The time average pulsatile pressure drop between the sudden enlargement drop-sill and downstream 74De is larger than that of steady flow, and the ratio of the former to the latter has positive correlation with pulsatile amplitude and frequency. The velocity profiles in the regions of separation, reattachment and re-development fluctuate periodically, and so as the recirculation length. The recirculation eddy strength, as well as the corner eddy strength, has positive relationship with the acceleration, for the acceleration intensifies the flow mixing in the recirculation zone and corner eddy, thus enhancing the dissipation of energy.
