一类新的被动型流动控制方法的物理机制研究

Flows over airfoils and turbine blades are often dominated by the effects of flow separation which can change the lift and drag characteristics of the airfoil or blade and thus result in a lower lift/drag ratio. In addition, the phenomenon of flow separation for turbomachinery internal flows can also lead to the occurrence of rotating stall and surge in a compressor. At present, most of the active control approaches can control the flow separation effectively, but a considerable price will usually have to be paid for application of these techniques; in contrast, passive control methods only work best in a relatively narrow range of circumstances and their flow separation suppression effect is also not very obvious. In this project, a novel passive flow control technique is proposed and studied. The technique will place a small structure such as cylinder or airfoil shaped blade near the upstream region of the point of flow separation on the blade wall, and thus uses the interaction between the boundary layer of the airfoil and the shedding of vortices from the installed small structure to suppress flow separation. In order to gain insight into the mechanisms behind the proposed method, high precision simulation techniques will be used to study the interaction between the blade boundary layer and the series of vortices shed periodically in the wake of the installed small structure. Special attention will be paid to the interactions occurring between different forms of turbulent structure at the point of separation. In addition, the optimum installation position and the shape of the added small structure will be obtained through parameter optimization in order to yield desirable results in the separation control of flow over the turbine blades. The feasibility of applying this new method to rotor blades of horizontal axis wind turbines or subsonic compressor stages will be also investigated with the aim of improving the aerodynamic performance of such turbomachinery. Finally, the effectiveness of the proposed method will be verified by experiment which will be carried out by means of particle image velocimetry (PIV) in a low-turbulence wind tunnel. Therefore, the overall goals of this proposal are not only to develop a new flow control method but also to reveal the physical mechanism of internal flow separation in-depth. It is expected that results from this study will be important for aeroengine designers to take into account the unsteady effects in the design process or provide theoretical basis for guidelines that should be followed during turbomachinery operation.

流动分离会降低叶片升阻比，诱发叶轮机械内旋转失速及喘振等现象。目前多数主动控制方法可显著控制叶片表面的流动分离,但通常需付出相当的代价；而多数被动控制方法存在有效工作范围较窄、效果不够显著等问题。本项申请提出在叶片分离点上游附近安装小圆柱或小叶片，利用这类小结构诱导涡与主叶片边界层之间的相互干涉来抑制流动分离。采用粒子图像速度场测量等技术、现代风洞试验手段和基于高精度分离涡的数值模拟方法，研究小结构诱导涡与边界层，特别是分离点附近湍流结构间的相互作用，揭示其抑制流动分离的机理，再通过对小结构的参数优化，获得最佳的结构形式与安装位置，从而有效控制叶片表面流动分离，并将此类流动控制方法应用于亚音速压气机及水平轴风力机叶片上，以提高动力机械气动性能。本项申请蕴藏着新的流动控制措施与对内部分离机理的进一步剖析和诠释，必将为叶轮机械在设计阶段考虑非定常效应和运行过程应该遵循的准则提供理论支撑。

叶片表面的流动分离会降低叶片升阻比，诱发叶轮机械内旋转失速及喘振等现象。目前多数主动控制方法可显著控制叶片表面的流动分离,但通常需付出相当的代价；而多数被动控制方法则存在有效工作范围较窄、效果不够显著等问题。本项目在此基础上提出了一种新的流动控制方法，即在叶片分离点上游附近安装小圆柱或小叶片，利用这类小结构诱导涡与主叶片边界层之间的相互干涉来抑制流动分离。项目采用粒子图像速度场测量等技术、现代风洞试验手段和基于高精度分离涡的数值模拟方法，研究小结构诱导涡与边界层，特别是分离点附近湍流结构间的相互作用，揭示其抑制流动分离的机理，再通过对小结构的参数优化，获得最佳的结构形式与安装位置，从而有效控制叶片表面流动分离，并将此类流动控制方法应用于亚音速压气机及水平轴风力机叶片上。研究结果表明：前缘微小圆柱可以显著提高翼型升力系数和升阻比，同时可以大大降低总体的阻力系数。雷诺平均模拟（RANS）和延迟分离涡模拟（DDES）两者结果都表明，微小圆柱这一控制装置可以有效延缓翼型深失速，同时减小翼型吸力面大范围的分离区域。此类流动分离控制方法可以显著抑制或推迟各类叶片表面上的流动分离，提高叶片的升阻比，使风力机叶片表面上的流动分离推迟2~4°，提升风力机的风能利用率，亦可显著推迟压气机内部的流动分离，提升压气机的气动性能。本项目提出了新的流动控制措施与方法，并对叶片表面的流动分离控制机理进行了进一步的剖析和诠释，将为叶轮机械在设计阶段考虑非定常效应和运行过程应该遵循的准则提供理论支撑。.本项目发表57篇国际期刊论文，47篇国内期刊论文，申请发明专利11个，获得授权发明专利11个，培养硕士25、博士研究生4、出站博士后1名。