等温-绝热边界对湍流热对流转捩特性的影响

本项目拟通过理论分析与数值模拟对不同的等温-绝热边界下湍流对流转捩机理进行深入系统的研究。探究具有不同有效等温占比η及周期宽高比φ的等温-绝热边界对湍流对流转捩过程中羽流的产生、演化及湍流的间歇性的影响；分析流场的时间平均特性和脉动特性，揭示等温-绝热边界下湍流热对流中的大尺度运动规律以及不同区域间湍流脉动强度的差异；建立等温-绝热边界下湍流热对流中，有效等温占比η以及周期宽高比φ与速度结构函数Su(r)、温度结构函数ST(r)的标度律之间的关联；明确不同的有效等温占比η以及周期宽高比φ对湍流热对流中表征换热效率的Nusselt数的影响规律；揭示不同的有效等温占比η以及周期宽高比φ对湍流RB系统中向湍流转变的转捩区以及“软湍流”向“硬湍流”转捩的影响规律。突破传统等温边界条件下的湍流热对流的转捩机理，诠释等温-绝热边界对湍流热对流转捩特性的影响规律。

Through theoretical analysis and numerical simulation, the turbulent convection transition mechanism under different isothermal-adiabatic boundary conditions is studied systematically in this project. The effects of isothermal-adiabatic boundary with different effective isothermal ratios η and periodic width to height ratios φ on plume generation, evolution and intermittency of turbulence during transition are investigated. The time-averaged characteristics and fluctuation characteristics of flow field are analyzed. The law of large-scale motion of turbulent thermal convection under isothermal-adiabatic boundary and the difference of turbulent fluctuation intensity between different regions are revealed. In turbulent thermal convection with temperature-adiabatic boundary, the correlation between effective isothermal ratio_and period width-height ratio_and scaling laws of velocity structure function Su(r) and temperature structure function ST(r). The influence of different effective isothermal ratios η and period width-height ratios φ on Nusselt number, which characterizes heat transfer efficiency in turbulent heat convection. The influence of different effective isothermal ratio and periodic width to height ratio on heat transfer efficiency in turbulent heat convection are clarified. The influence of different effective isothermal ratios and periodic width to height ratios on turbulent RB system when transition from soft turbulence to hard turbulence. This project breaks through the transition mechanism of turbulent heat convection under the traditional isothermal boundary conditions and explains the influence of isothermal-adiabatic boundary on the transition characteristics of turbulent heat convection.