Swirling-strength based large eddy simulation of turbulent flow around single square cylinder at low Reynolds numbers

In view of the fact that large scale vortices play the substantial role of momentum transport in turbulent flows, large eddy simulation(LES) is considered as a better simulation model. However, the sub-grid scale(SGS) models reported so far have not ascertained under what flow conditions the LES can lapse into the direct numerical simulation. To overcome this discrepancy, this paper develops a swirling strength based the SGS model to properly model the turbulence intermittency, with the primary characteristics that when the local swirling strength is zero, the local sub-grid viscosity will be vanished. In this paper, the model is used to investigate the flow characteristics of zero-incident incompressible turbulent flows around a single square cylinder(SC)at a low Reynolds number range Re ∈ [103, 104]. The flow characteristics investigated include the Reynolds number dependence of lift and drag coefficients, the distributions of time-spanwise averaged variables such as the sub-grid viscosity and the logarithm of Kolmogorov micro-scale to the base of 10 at Re = 2 500 and 104, the contours of spanwise and streamwise vorticity components at t = 170. It is revealed that the peak value of sub-grid viscosity ratio and its root mean square(RMS) values grow with the Reynolds number. The dissipation rate of turbulent kinetic energy is larger near the SC solid walls.The instantaneous factor of swirling strength intermittency(FSI) exhibits some laminated structure involved with vortex shedding.     

煤粉预燃室内气体湍流交换系数的实验和数据整理

一、引言 旋流式煤粉预燃室作为一种新型粉煤燃烧器,在降低电站锅炉点火用油,提高煤粉锅炉的低负荷稳燃性能等方面发挥了显著的怍用.旋流式煤粉预燃室合理地组织了旋转射流、环形射流,有其独特的结构和配风方式,其稳燃机理尚不完全清楚.本文作者则在预燃室冷态流动模型上用温度示踪方法试验研究了有根部风的改进型预燃室内气流的混合过程,并用三孔测速探针测量了筒内八个断面上的轴向和切向速度分布,对预燃室内部