布朗运动和湍流扩散作用下槽流中纤维悬浮流动特性的研究  

Flow property of fiber suspension in a turbulent channel flow under considering both Brownian and turbulent diffusions

作　　者：夏懿[1] 库晓珂[1] 沈苏华[1] 

机构地区：[1]浙江大学航空航天学院力学系,杭州310027

出　　处：《物理学报》2016年第19期177-190,共14页Acta Physica Sinica

基　　金：国家自然科学基金重大项目(批准号:11132008)资助的课题~~

摘　　要：为了探讨槽道中纤维悬浮湍流场特性,本文对修正的雷诺平均纳维-斯托克斯方程、含纤维项的湍动能和耗散率方程、纤维动力学方程以及纤维取向概率密度函数方程进行了数值研究,同时进行了相关实验以验证计算结果.研究结果表明,流场中尤其是近壁区域,纤维取向趋向于与流动方向一致,且该现象随着雷诺数和纤维浓度的减小以及纤维长径比的增大而更为明显.纤维在槽道中分布不均匀,但随着雷诺数的增大和纤维长径比的减小趋于均匀.相对于单相流,纤维悬浮流的流向平均速度剖面更陡峭,且剖面斜率随着纤维浓度、长径比的增大以及雷诺数的减小而变大,纤维的存在使湍流场的湍动能和雷诺应力减小,且减小程度随着纤维浓度和长径比的增大以及雷诺数的减小而增加.流场中的第一法向应力差小于0.05且远小于剪切应力.从壁面到中心,剪切应力增加而第一法向应力差减小.剪切应力和第一法向应力差都随着纤维浓度和长径比的增大而增大.随着雷诺数的增大,剪切应力增大而第一法向应力差减小.纤维浓度对于剪切应力和第一法向应力差的影响比纤维长径比更显著.The issue of fiber suspension flow has received great substantial attention in the last decades. In contrast with the abundant researches of normal size fiber suspensions flow, this paper is devoted to the small size fiber suspension composed of water and polyarmide fiber where Brownian motion plays an important role and thus cannot be neglected.The spatial distribution and orientation of fiber, streamwise mean velocity profile, turbulent kinetic energy, Reynolds stress and rheological property of fiber suspension in a turbulent channel flow are obtained and analyzed both numerically and experimentally. To simulate the small fiber suspension flow well, the well-known Reynolds averaged Navier-Stokes（N-S） equation governing the suspension flow is modified in consideration of the effect of fibers on base flow. The equation describing the probability density functions for fiber orientation is derived in view of the rotary Brownian diffusion. The general dynamic equation for fibers is reshaped in the effect of spatial Brownian diffusion. For the sake of the closure of the N-S equation, the turbulence kinetic energy and turbulence dissipation rate equations with fiber term are employed.The conditional finite difference method is adopted to discrete these partial differential equations. And the diffusion term and convective term are discretized by the central finite differences and the second-order upwind finite difference schemes,respectively. The second and fourth-order orientation tensors are integrated by the Simpson formula. Experiment is also performed to validate some numerical results. The results show that most fibers tend to align parallelly to the flow direction in the flow, especially in regions near the wall. Such a phenomenon is more obvious with the decreases of Reynolds number and fiber concentration, and with the increase of fiber aspect ratio. Fiber volume fraction distribution is non-uniform across the channel, and becomes more uniform with increasing Reynolds number, and with reducing fiber aspec

关 键 词：纤维悬浮流 布朗扩散 湍流扩散 流变特性 

分 类 号：O357.5[理学—流体力学]