In order to avoid model support interference, the flow over cylinders of varying fineness ratio (length /diameter) aligned with the free stream were examined using a magnetic suspension and balance system. The drag coefficient variation of a right circular cylinder was obtained for a wide range of fineness ratios. Particle Imaging Velocimetry (PIV) was used to examine the flow field, particularly the behavior of the leading-edge separation shear layer and its effect on the wake. Reynolds numbers based on the cylinder diameter ranged from 5x104 to 1.1x105, while the major portion of the experiment was conducted at the ReD= 1.0x105. For the moderately large fineness ratio, the shear layer reattaches with subsequent growth of the boundary layer, whereas over shorter cylinders, the shear layer remains detached. Differences in the wake recirculation region and the immediate wake patterns are clarified in terms of both the mean velocity and turbulent flow fields, including longitudinal vortical structures in the cross-flow plane of the wake. The minimum drag corresponded to the fineness ratio where the separated shear layer reattached at the trai領(lǐng) edge of the cylinder. The base pressure was obtained with a telemetry technique. Pressure fields and aerodynamic force fluctuations are also discussed. 德國(guó)LaVision PIV/PLIF粒子成像測(cè)速場(chǎng)儀 Imager SX PIV相機(jī) 用于粒子成像測(cè)速(PIV)的熒光示蹤粒子