复杂湍流系统中大尺度结构及其对输运特性影响的研究

Large-scale structures in turbulent flows which depend on the energy injection, geometric boundaries and other factors, play a leading role in heat and mass transfer processes, and their generation mechanisms and effects on heat and mass transfer are unsolved, thus in-depth study of turbulent large-scale structures is necessary. This application is to carry out experiments, numerical simulations and theoretical studies in three typical turbulent flows: free shear turbulence, wall-bounded turbulence and turbulent convection. The main concern is to focus on the coupling between large- and small- scale structures, mass and heat transport properties between these structures of different scales (such as counter-gradient transport, inverse cascade). To achieve this, first, the combination of Tomo-TRPIV, PLIF and HWA etc will be used to measure high-resolution data for both velocity and scalar fields, and DNS (and LES) will be carried out. Second, HHT-based and wavelet transform-based methods will be developed and applied to analyze the nonlinear characteristics and memory effects of the large-scale turbulent structures, the counter-gradient transport of heat and mass transfer, and the inverse cascade process. Third, multi-scale expansion method will be used to reveal in detail the interaction between structures with different scales, and the scale-dependent contribution of structures on heat and mass transfer. The knowledge of large-scale structures and particularly the knowledge of its transport mechanism are of significant importance to the study of turbulence mechanism, and further, this knowledge can be helpful to solve complex engineering turbulence problems.

湍流大尺度结构依赖于能量注入方式、流动几何边界等因素，在传热、传质等物理过程中起主导作用，需要深入研究其物理机理。本申请以自由剪切湍流、壁湍流和湍流热对流三个复杂系统为研究对象，开展实验、数值和理论研究，重点关注大尺度结构与小尺度结构间的耦合作用形式和其中的能量传递(包括逆梯度输运、逆级串)规律，以及对输运和扩散过程的影响。实验上采用Tomo-TRPIV、PLIF等湍流测量技术，对速度场、标量场开展高精度同步测量，捕捉大尺度湍流结构，并开展相应的数值模拟研究；采用HHT和子波变换等分析方法，对大尺度湍流结构中的非线性特征、记忆效应、逆梯度输运和逆级串过程进行刻画；理论上采用多尺度展开分析，揭示大尺度结构与其它结构间的相互作用规律，刻画不同尺度对传热、传质的贡献。对湍流大尺度结构，特别是输运机理的认识和理解，对湍流机理探讨具有重要意义，并为解决工程中的湍流问题提供坚实的实验和理论基础。

湍流流动中存在多种尺度的涡旋结构，其中的大尺度结构与流动几何边界和能量注入方式等因素密切相关，并在湍流传热、传质等物理过程中起重要作用。课题针对壁湍流和湍流热对流和环境湍流等，开展实验、数值和理论研究，重点关注大尺度结构与小尺度结构间的耦合作用形式和其中的能量传递(包括逆梯度输运、逆级串)规律，以及对输运和扩散过程的影响。采用Tomo-TRPIV、PLIF等湍流测量技术，对速度场、标量场开展高精度同步测量，捕捉大尺度湍流结构，并开展相应的数值模拟研究；采用HHT和子波变换等分析方法，对大尺度湍流结构中的非线性特征、逆梯度输运和逆级串过程进行刻画；理论上采用多尺度展开分析，揭示大尺度结构与其它结构间的相互作用规律，刻画不同尺度对传热、传质的贡献。项目成果集中在三个方面：一、精细刻画了复杂边界条件下的湍流大尺度结构时空演化特征，湍流结构与壁面减租的关系；二、RT和海洋湍流中的能量耗散与级串与相关尺度分析；三、环境和生物湍流系统中被动和主动标量湍流结构及对颗粒扩散的影响。项目成果对理解复杂系统中湍流结构生成和演化，质能输运以及减租机理具有重要理论意义，并能为解决工程中的湍流问题提供坚实的实验和理论基础。