基于旋流强度亚格子模型的湍流间歇性研究

在大Re数下观察到的湍流, 是流体力学的众所周知的难点和研究热点, 广泛出现在工业、农业的流体工程和大自然环境中。观测表明，湍流流动体现在旋涡的运动。湍流中互相拉伸挤压的旋涡，导致很不规则的速度脉动、温度和质量分数脉动，而这些脉动具有很大的时、空尺度范围。要在全尺度上对湍流进行探索，只有在雷诺数比较低时才是可行的。考虑到湍流的大尺度旋涡， 对动量、能量和质量传递和输运起主导作用，计算湍流的大涡模拟（LES）方法, 前景看好. 已经发展的亚格子模型, 却没有明确大涡模拟可被直接数值模拟替代的条件。为了克服这一缺陷, 本项目拟以旋流强度为基础, 建立一种新的亚格子模型, 以研究湍流的间歇性。拟对槽道流、方腔中的自然对流和尾迹流等流体力学和传热学的标准问题, 自行开发模拟程序, 进行湍流的大涡模拟。这种新提的亚格子模型, 主要特点为: 在湍流场中, 当地旋流强度为零时, 当地亚格子粘性必然消失。

Generally observed at large Reynolds numbers, turbulence is a well-known difficulty and a hot point of research, it is widely occurred in the natural environment and the industrail、argricultrial engineering fluid flows. Observation and measurement indicate that turbulent flows can be incarnated by the motion of vortices. The mutually stretching and compressing of vorticies in turbulent flows lead to irregular fluctuations of velocities、temperature and mass fractions, which have broad spatial-temporal scale ranges. To explore turbulence at a full scale level, it is merely applicable in the case of comparatively low Reynolds number. Considering the substantial role of momentum transport and heat and mass transfer is played by large scale vortices in turbulent flows, the large eddy simulation(LES) of turbulent flows is expected to be a better simulation tool. The sub-grid models already reported in publications, havenot ascertained that under what kind of flow condition the direct numerical simulation can alternate the LES. Therefore, to overcome this discrepancy, we will use the concept of swirling strength to develop a swirling strength based sub-grid model for investigating the turbulence intermittency. We will design and develop the LES simulator and investigate the benchmarks in fluid mechanics and thermal science, such as the turbulent channel flows，the turbulent natural convection in a differentially heat cavity and wake flow, etc. For the to be proposed new sub-grid model, its primary characterics is: when the local swirling strength is zero, the local sub-grid viscosity must be vanished.