三维湍流热对流中non-Oberbeck-Boussinesq效应对羽流的影响研究

In turbulent thermal convection plume is the most important coherent structure which is also the main carrier of heat transfer. This project is devoted to numerically study the influence of non-Oberbeck-Boussinesq (NOB) effects induced by large temperature difference on plumes in turbulent thermal convection. Low-Mach-number Navier-Stokes (NS) equations are exploited. The morphological evolution of plumes and the statistics of plumes are the two issues in this project. Plumes could be attracted directly from flow filed or/and from temperature-time series by cliff-ramp structure. First, influence of NOB-I effect, namely temperature-dependence of fluid properties, is considered, especially on the morphological evolution of sheet-like plumes near boundary layer. Secondly, influence of NOB-II effect is studied, especially compressibility by large temperature difference on the statistics of plumes. In the end, from respects of inhomogeneity of fluid properties, large-temperature-difference-induced compressibility and breaking of up-down symmetry, physical explanation will be rendered to uncover the mechanism of influences on plume evolution and statistics and to provide valuable reference for engineering application.

羽流是湍流热对流中最重要拟序结构，也是传热的主要载体。本项目针对羽流的形态演化过程和统计分布规律，采用小马赫数Navier-Stokes (NS)方程模型，通过直接数值模拟研究湍流热对流中大温差导致的non-Oberbeck-Boussinesq (NOB)效应对羽流的影响。羽流可以从流场直接提取或者利用cliff-ramp结构从温度时间序列中提取。首先考察第一类NOB效应，即物性参数的温度依赖性，对羽流的影响，重点分析边界层附近的片状羽流的演化及相互作用规律。其次考察第二类NOB效应对羽流的影响，着重分析大温差导致的可压缩效应对羽流统计分布规律的影响。最后，根据速度边界层和热边界层的不同耦合形式，考察NOB效应的影响差异。从物性的空间分布不均匀性、大温差导致的可压缩效应以及系统的对称破缺等角度出发，揭示NOB效应的影响机理，为工程实践提供有益参考。

本项目针对羽流的形态演化过程和统计分布规律，采用小马赫数NS方程模型，通过直接数值模拟研究湍流热对流中大温差导致的NOB效应对羽流的影响。从流场中直接提取或者利用cliff-ramp结构从温度时间序列中提取羽流结构。考察第一类NOB效应，即物性参数的温度依赖性，对羽流的影响，分析边界层附近的片状羽流的演化及相互作用规律。考察第二类NOB效应对羽流的影响，着重分析大温差导致的可压缩效应对羽流统计分布规律的影响。根据速度边界层和热边界层的不同耦合形式，考察NOB效应的影响差异。从物性的空间分布不均匀性、大温差导致的可压缩效应以及系统的对称破缺等角度出发，揭示NOB效应的影响机理。