| Summary: | 碩士 === 國立臺灣科技大學 === 機械工程系 === 101 === The surface flow characteristics and the wake instability of a two-dimensional square cylinder controlled by up-wind jet injection were experimentally investigated. The characteristic flow patterns were observed by flow visualization. The wake and the jet instability characteristics were detected simultaneously by using a two one-component hot-wire anemometer. The flow field around the upstream cylinder surface was measured by a particle image velocimeter (PIV). The results of flow visualization showed that the features of flow were strongly subjected to the influences of the injection ratio R and Reynolds number Rew. At R < 1.0, the jet presented up-down flapping motion (which was denoted as the flapping mode). The flapping frequency coincided with the vortex shedding frequency. At 1.0 < R < 4.0, the jet deflected and attached to the upsurface of the cylinder, the jet column oscillated back-and-forth periodically (which was designated as the deflection with oscillation mode). The oscillating frequency of the jet column was the same as the vortex shedding frequency. At 4.0 < R < 8.0, the jet deflected without oscillation and did not attach to the upstream surface of the cylinder (which was designated as the deflection without oscillation mode). At R > 8.0, the jet presented unsteady up-down flapping motion (which was denoted as the jet-type mode). The main frequency in the flapping and the oscillation modes increased with increasing R and Rew. The flapping motion of the jet was induced by the oscillation motion of the vortical flow structure in the wake.
|
|---|
