Abstract
Unsteady wake structures around a bluff body, which has a slanted rear surface, is investigated experimentally with measuring the velocity and the pressure fields. Velocity distribution obtained by a Particle Image Velocimetry showed that vortices are intermittently generated and occasionally it grows to large-scale vortex which separates the flow from the slanted surface. From the pressure distribution, which is simultaneously measured with the velocity field, it is clarified that the large-scale separated vortex has considerable extent in the spanwise direction. This fact suggests that the re-attachment line of the downwash is completely separated from the slanted surface when the largescale vortex is generated. From the time-frequency analysis, which is applied to the velocity fluctuation measured by hot-wires, the flow observed at downstream of the body exhibits the periodic fluctuation, whereas the flow near the slanted surface does not involve the periodic fluctuations. Instead, the intermittent fluctuation is observed for the case that the downwash of the flow structure is separated from and re-attaches to the slanted surface. The intermittent fluctuation on the slanted surface is observed regardless of the existence of upwash, whereas the periodic fluctuation at the downstream vanished when the upwash is absent.
