摘要
对Reλ约为51均匀各向同性湍流内Stk(=τp／Tk)为0-10.0的有限惯性颗粒的碰撞行为进行了直接数值模拟,以研究湍流对有限惯性颗粒碰撞的影响．结果表明,具有一定惯性颗粒的湍流碰撞率完全不同于零惯性的轻颗粒(Stk=0)和可忽略湍流作用的重颗粒(Stk→∞),其变化趋势极其复杂:在Stk为0-1．0之间,颗粒的碰撞率随St的增加而近乎线性地剧烈增长,在Stk≈1．0和3．0(对应的StE=τp／Te≈0．5)附近,颗粒碰撞率出现两个峰值,在Stk>3．0以后,颗粒的碰撞率随惯性增大而逐渐趋向于重颗粒极限;在峰值处,有限惯性颗粒的平均碰撞率的峰值较轻颗粒增强了30倍左右．为进一步分析湍流作用下颗粒碰撞率的影响因素,分别使用可能发生碰撞的颗粒对的径向分布函数和径向相对速度来量化颗粒的局部富集效应和湍流掺混效应,表明Stk≈1．0时局部富集效应最为强烈,使得颗粒的碰撞率出现第1个峰值;湍流掺混效应则随着颗粒Stk的增大而渐近增大;局部富集和湍流掺混联合作用的结果,使得颗粒碰撞率在Stk≈3．0附近出现另一个峰值．
In this paper, direct numerical simulations （DNS） were conducted to study particle collisions in stationary isotropic homogeneous turbulent flow, with the aim to investigate the turbulence influence on collision rates of various inertia particles. It is found that the collision behavior of finite-inertia particle is very complicated, both the Saffman ＆Turner＇s theory （Stk =τp/τk= 0） and kinetic theory （Stk→∞） can not correctly predict it. For particles of Stk 〈 1.0 the collision rate increases sharply as Stk increases; at Stk -1.0, collision rate reaches a peak value; as Stk continues to increase, collision rate slowly decreases at first and then increases to reach another peak at Stk -3.0 （corresponding to Eulerian integral time scale）. For larger particles collision rate decreases slowly to coincide with the kinetic theory as particle inertia continues to increase. Both of the peak value are about 30 times of zero inertia limit. To further understand the mechanism of finiteinertia particle collision in isotropic turbulence, two major effects of turbulent flow on particle collision, namely turbulent mixing effect and preferential concentration effect, are investigated and are represent qualitatively using radial relative velocity 〈｜wr｜〉 and radial distribution function g（R） of colliding particle pairs, respectively. Both effects tend to increase collision rates, leading to the observed complex behavior. The results showed that preferential concentration effect is the main contribution factor for the peak of particle collision rate near Stk - 1.0, while both preferential concentration effect and turbulent mixing effect contributing to the peak near Stk-3.0, with much stronger turbulent mixing effect herein.
出处
《力学学报》
EI
CSCD
北大核心
2006年第1期25-32,共8页
Chinese Journal of Theoretical and Applied Mechanics
基金
国家重点基础研究发展计划(2002CB211600)教育部新世纪创新人才计划(NCET-04-0708)资助项目~~
