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Experimental Study of Stationary and Oscillating Circular Cylinders in a Tandem Arrangement
|關鍵字:||bistable;雙穩定;critical spacing;tandem arrangement cylinders;lock-on boundary;臨界間距;縱列雙圓柱;鎖定邊界||出版社:||機械工程學系||摘要:||
The vortex shedding for two identical circular cylinders in a tandem arrangement have been studied experimentally. The experiments were performed in an open-type wind tunnel for Reynolds number raging from 4500-15000. In addition to the case of two stationary cylinders, the oscillating case involves a rotationally oscillating upstream cylinder. The vortex shedding frequency, lock-on regime, surface pressures, drag forces, and vortical structure of the near wake are described.
At the critical spacing where the dual vortex shedding frequencies take place have been observed for the stationary case well as for the oscillating case. The occurrence of dual shedding frequencies indicates switching of the flow patterns between two stable states and is referred to as the bistable flow. Moreover, the two shedding frequencies appeared intermittently, in which the lower frequency results from the vortex shedding behind the downstream cylinder and the higher frequency from the upstream cylinder.
In the oscillating case, research is emphasized on the control of the bistable flow. This is attained by rotationally oscillating the upstream cylinder while holding the downstream cylinder stationary. The vortex shedding from a rotationally oscillating cylinder is found to lock-on to the external forcing at certain oscillation frequency and amplitude. As the spacing between the cylinders is increased, the lock-on boundary moves toward higher frequencies, and progressively close to that for a single oscillating cylinder. The bistable flow could also occur when the vortex shedding is locked-on to the oscillating upstream cylinder. The effects due to vortex lock-on and bistable shedding are reported and discussed in detail.
|Appears in Collections:||機械工程學系所|
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