基于壁面弯曲肋条结构的湍流减阻被动控制研究

Riblets aligned in the streamwise is a kind of passive control techniques that has very good prospects for the wide scope, convenient application and maintenance. But in the practical applications, the wide economic benefit of riblets can’t be obtained for its high cost and low rate of drag reduction. By introducing the spanwise velocity component, a much bigger of drag reduction rate can be obtained by the recent curved riblets. However, the related research is very lacking, motivated by the above issues, the project intends to undertake the following works: (1)The database of turbulent channel flow with curved riblets on the wall will be firstly established via direct numerical simulation. Based on the database, the dynamic evolution process of the near wall coherent structure, the self-sustaining mechanism of near wall turbulence as well as the interaction between the riblets and the coherent structure etc. will be explored to reveal the mechanism of drag reduction in different aspects.(2) The relationship between the drag reduction and all the parameters, such as the height of the riblet, the width of the riblet, the space between the riblets, the amplitude and the wave length will be investigated and the key parameters of drag reduction will be determined for curved riblets using the fully developed turbulent channel flow. After that, the optimal parameter combination as well as the biggest drag reduction rate will be discussed. For further verification, the drag reduction of curved riblets on a wind turbine airfoil will be studied.In summary, the project can deepen the understanding of the mechanism of drag reduction for curved riblets, and also provide important theoretical basis for the design of curved riblets for application.

肋条减阻是一种适用范围广、应用维护方便、具有良好应用前景的湍流减阻被动控制技术。但在实际应用中，因其制造、使用成本高且减阻率较低，目前仍无法产生广泛的经济效益。新型弯曲肋条通过引入展向振荡速度使肋条减阻效果大幅提高，但相关研究还非常匮乏。本项目将围绕弯曲肋条减阻这一科学问题开展以下研究工作：（1）采用直接数值模拟方法，建立弯曲肋条槽道湍流数据库，并基于该数据库，探讨弯曲肋条近壁相干结构的演化机制和自维持机理，分析弯曲肋条和近壁相干结构的相互作用，多角度揭示弯曲肋条的减阻机理。（2）通过弯曲肋条槽道湍流直接数值模拟，研究弯曲肋条减阻率随肋条高度、肋条宽度、肋条间距、幅值、波长等参数的变化规律，确定弯曲肋条减阻的关键因素，探讨弯曲肋条的最优参数组合和最大减阻率。在此基础上，以风力机翼型为对象，进一步考察弯曲肋条的减阻效果。项目旨在加深对弯曲肋条减阻机理的认识，为弯曲肋条减阻设计提供理论依据。

湍流高摩擦阻力问题广泛地存在于实际工程应用中，如航空运输，石油管道，水下潜艇，风力发电等。通过弯曲肋条被动控制和相关主动控制方案是实现流动减阻的有效手段。围绕湍流减阻机理、弯曲肋条等湍流减阻控制这一科学问题，项目开展了以下工作（1）从能量传递、雷诺应力输运等多角度揭示了近壁湍流减阻机理，探明了雷诺应力再分配对湍流减阻的关键作用。系统研究了壁面可测信号和近壁流向涡的关系，提出了压力信号和壁面流向涡关系的新模型。通过引入随机干扰首次揭示了壁面流向摩擦力对流向涡探测的失效机理。（2）以风力机翼型为研究对象，采用CFD对直肋条和弯曲肋条控制效果进行了数值仿真，研究发现曲肋条可以有效减小翼型表面摩擦阻力，但同时会增加压差阻力。相对于主动控制，弯曲肋条环境适应性较差，所需尺度较小。（3）基于壁面展向摩擦力和压力信号，提出了抑制近壁流向涡的新方法，获得了高达16%的减阻效果。考虑控制元件形状的影响，提出了新的基于壁面运动凹坑/凸丘的湍流减阻控制策略。除此之外，项目还对其他前沿问题开展了探索研究如基于同向射流的风力机翼型增升减阻方法，大型风力机叶片气动设计理论和方法等。总之，本项目增加了湍流减阻机理的认识，提高人们对弯曲肋条等控制方案的理解，的较好的完成了项目计划和目标，取得了较为丰富的研究成果。