Alternative Control of Fluctuation Frequency in the Wake of a Rectangulay Cylinder near the Critical Shape

采用离散涡方法，对均匀流场中矩形柱体在临界形状附近前缘抽吸触发的完全分离流与周期性再附着流的交替控制进行了数值模拟。根据数值模拟的结果，在制备矩形柱体后，在前缘处的抽吸槽连接到抽吸装置，其中抽吸速度和操作时间是可控的。通过数值模拟和实验研究得到以下主要结果：1.在临界形状圆柱绕流中，小侧高比圆柱绕流中出现的完全分离流脉动叠加在大侧高比圆柱绕流中出现的周期性再附着流上。在实验中出现了间歇性的波形，而在数值模拟中出现了假想的波形 ...更多信息 在运行时间内，单次抽吸将流动转换为周期性再附着流动，抽吸速度为入射流的0.4-0.7倍，脉动周期为全分离流的1/30，经过一段时间后，转换后的流动又恢复到临界流动。吸风宽度为半筒高时，过渡段的吸风宽度较合适。在数值模拟中，在3.6 ~ 4.0的侧高比范围内，可以实现这种控制。3.在实验中，在低雷诺数和高雷诺数下，在侧高比分别为2.7和2.3时，可以实现临界形状。结果与数值模拟结果在定性上相似，但在定量上存在一些差异，如转捩发生在比数值模拟结果高0.7-1.0倍的吸速处，全分离流动的脉动周期比数值模拟结果长0.1-0.4倍，4.上述差异以及在抽吸后的几个阶段出现的延迟转捩等问题有待进一步研究。少

Numerical simulation by discrete vortex method was carried out on the alternative control between wholly separated flow and periodically reattached flow, triggered off by suction at a leading edge of a rectangular cylinder near the critical shape in a uniform flow. Experiments were executed after preparing rectangular cylinders with the suction slot at the leading edge connected to a suction device in which suction speed and operating time were controllable, based on the results of the numerical simulation. The main results obtained through the simulation and the experiments are the following.1.In the flow around a cylinder with the critical shape, fluctuation in wholly separated flow appeared in the flow around a cylinder with small side-to-height ratio are superposed on periodically reattached flow appeared in the one with large side-to-height ratio. They appear intermittently in the experiment, while supperposed wave form appears in the simulation.2.In the numerical simulation, the … More flow was transferred to the periodically reattached flow by a single suction which had 0.4-0.7 times speed in the incident flow and 1/30 of fluctuating period in the wholly separated flow for the operating time, and the transferred flow returned to the critical flow after a while. The suction width with a half of the height of cylinder was suitable to the transition. This control was possible in the range of side-height ratio between 3.6 and 4.0 at which the critical shape was realized in the numerical simulation.3.In the experiment, the critical shape was realized at 2.7 of side-height ratio at low Reynolds number and 2.3 at high Reynolds number. The results were similar qualitatively to those of the numerical simulation, but, quantitatively, some differences appeared such as the transition occurred at 0.7-1.0 times of the suction speed higher and for 0.1-0.4 times fluctuating period in the wholly separated flow of operating time longer than the numerical results, and the suitable width for the suction control was below 0.2 times the height.4.We have some problems to be investigated such as the differences above-mentioned and the retarded transition occurred at a few periods after the suction. Less