钝体绕流广泛存在于自然界和工程领域。方柱是一种经典的钝体模型，其绕流中的尾迹涡周期性脱落会诱发结构振动和噪声，危害桥梁、建筑物安全，降低舰船隐蔽性。本项目围绕来流与方柱表面作用的临界点——前驻点开展研究，采用合成射流主动流动控制技术来控制方柱绕流的流动分离、尾迹涡脱落以及阻力特性。首先，借助高时空分辨率的粒子图像测速技术获得无控制时方柱前驻点位置随时间和雷诺数的变化规律，研究前驻点的运动与尾迹涡脱落的联系。其次，在方柱迎风面布置狭缝合成射流，通过调节狭缝宽度来改变合成射流对称扰动的初始作用范围，研究前驻点区域内合成射流对称扰动/流场固有反对称扰动的竞争关系，揭示其对流场特性的影响规律和机理。最后，给出合成射流控制方柱绕流最佳减阻效果的参数组合。上述研究能揭示合成射流与钝体绕流相互作用的机制和分离流动控制的机理，对工程应用中方柱形结构的减振、降噪和减阻具有重要的指导意义。

Flow around a bluff body is a common phenomenon in nature and engineering applications. Square cylinder is one classic type of bluff body. The periodic wake vortex shedding can induce structural vibration and noise, thus threatening the safety of bridges and tall buildings, and reducing the concealment of ships. In this proposal, researches are carried out based on the front stagnation point, which is the critical point of the interaction between the incoming flow and the surface of square cylinder. The synthetic jet active flow control technology is used to control the flow separation, wake vortex shedding and drag coefficient of a square cylinder. Firstly, using the high spatial and temporal resolution particle image velocimetry technique, the variation of the front stagnation point position of the square cylinder with time and Reynolds number is obtained without flow control, and the relationship between the unsteady motion of front stagnation point and wake vortex shedding is explored. Secondly, the slot synthetic jet is placed on the front surface of the square cylinder, and the slot width is adjusted to change the size of region excited by the symmetrical disturbances of the synthetic jet. The initial competition between the symmetric disturbances of synthetic jet and the inherent antisymmetric disturbances is investigated in the front stagnation region, and its influence on the characteristics of the whole flow field and its mechanism are revealed. Finally, the combination of parameters with the most drag reduction is proposed. This research can reveal the interaction mechanism between synthetic jet and flow around bluff body, as well as the control mechanism of flow separation. It has important guiding significance for the reduction of vibration, noise and drag for structures with square cross section in engineering applications.