超声速非圆管射流的微楔控制

Compared with the circular jets, the axis switching phenomena of non-circular jets can significantly enhance the entrainment of jet and ambient gases. Therefore, non-circular jets have been the hotpot of related research fields. In addition, previous studies showed that the micro-ramp as a classical technology for passive flow separation control, had been proven effective in enhancing mixing in supersonic flow. Based on above phenomena, this project propose for install the micro-ramp in the non-circular nozzle, and investigate the effect of the micro-ramp on the flow structures of unsteady supersonic jets and their mixing properties for achieving the enhancement of the supersonic jet entrainment and mixing. We plan to combine the methods of experiment, theoretical analyses and numerical simulations, to study firstly the flow characteristics within the primary vortex loop of supersonic non-circular jets, then discuss the self-induced deformation of asymmetric vortex loop, the flow characteristics of streamwise vortex pairs and their effect on entrainment efficiency, and finally reveal the internal mechanism of their highly entrainment rate. Furthermore, the jet entrainment can be achieved optimum by changing the size and arrangement of the micro-ramp, which can provide important guidance for corresponding nozzle design.

与圆管射流相比，非圆管射流的轴置换现象可有效提高射流对环境流体的卷吸，因此非圆管射流一直是相关行业的研究热点。另外研究表明，微楔作为一种经典的流体分离被动控制方法，它能有效提高超声速流体的混合。基于此，本项目提出在非圆管喷嘴出口加装微楔，研究其对非定常超声速射流结构及混合特性的影响，以实现强化超声速射流卷吸与混合的目的。本项目拟综合实验、理论分析与数值模拟，从研究超声速非圆管射流的初始主涡环内部流动特征着手，探讨非圆涡环的自诱导变形、流向涡对的流动特征以及对卷吸效果的影响，揭示其高卷吸率的内在机制。另外，还通过改变微楔尺寸与分布，得到具有最佳卷吸效果的微楔尺寸与布置方式，为相关行业提供重要依据。

本项目按项目申请书所提研究内容，开展了强化超声速非圆管射流混合效果的研究，探讨了喷管周向曲率变化与加装微楔对射流结构和卷吸率的影响，得到了具有最佳卷吸效果的喷管形状。研究表明，喷嘴周向曲率不一致导致的涡环自诱导变形而形成反向流向涡对，同时流向涡的诱导速度加速了涡环的变形，因此涡环自诱导变形与流向涡对的共同作用强化了射流混合。另外，拐角的存在能加快非圆涡环的变形，因此在相同短长轴比（AR）下，矩形射流的卷吸率明显高于椭圆射流，且射流卷吸随AR减少而增大（2018，Computer and Fluids）。对于超声速非圆管射流，周向曲率不一致还会导致射流域内出现复杂的激波结构，且激波结构在射流边界变形过程中起主导作用（2017，International Journal of Heat and Mass Transfer）。此外，由于在微楔下游产生的三对反向旋转流向涡对、链式涡环及发卡涡结构，其改变了射流流场的速度剖面和形状，因而能强化射流对环境流体的卷吸。另外，研究表明，当微楔安装角度为45°和90°、安装间距为4h时，混合层获得最佳的卷吸效果。本研究成果对强化射流混合、提高燃烧效率和降低噪声等方面具有极其重要的意义。