静止円柱表面に発達する速度境界層および剥離せん断層の熱線流速計計測

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  • Hot-wire anemometer measurements of velocity boundary layers and separated shear layers developing on the surface of a stationary cylinder

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<p>A Kalman vortex street is generated in the wake of a circular cylinder placed in the flow. Visualization experiments have shown that the formation process of a Karman vortex street begins with the separated of a velocity boundary layer from the surface of the cylinder, the growth of minute disturbances in the separated velocity shear layer, and the transition to turbulence, followed by the gathering of multiple disturbances to form a vortex about the size of the cylinder's diameter. In this study, a hot-wire anemometer, which has a proven track record in measuring velocity boundary layers such as flat plates, is used to measure the velocity in the boundary layer. The hot-wire anemometer used was a self-made one, with a C-shaped sensor section to avoid disturbing the flow, and the sensor was inserted from the direction perpendicular to the flow. As a result, the formation process of the Karman vortex street in this case began to be disturbed by instability when the separated shear layer was about x/D=0.5. At x/D=2.5, a disturbance with a Strouhal number of about 0.2, which corresponds to the Kalman vortex street, occurred and grew downstream. The results show that the growth scenario is similar to that reported in previous visualization experiments.</p>

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