【作者】 游振江；

【导师】 林建忠；

【作者基本信息】 浙江大学 ， 流体力学， 2003， 博士

【摘要】 纤维悬浮流是指固体纤维粒子悬浮在液体或气体中形成的混合流动，在化工、纺织、造纸、医疗、环保、复合材料生产、食品加工等许多工业领域都有广泛应用。纤维悬浮流的研究还涉及多个学科分支，具有重要的理论意义。本文运用理论分析、数值计算以及实验的方法，对纤维悬浮流动稳定性相关问题进行了深入研究。 首先综合应用流体动力稳定性理论、细长体理论以及纤维方向张量工具，对纤维悬浮流进行线性稳定性分析，推导槽流和管流的稳定性方程，并对槽流导出在不同的稳定性分析模式以及不同的方向张量封闭格式下的多种形式方程。数值求解稳定性方程得到悬浮流的稳定性特征，发现纤维参数H值和水动力相互作用系数C₁的增加导致流动临界Re数增大，不稳定扰动的最大增长率降低，扰动失稳范围缩小。扰动速度的分布特征与发展规律也说明纤维的综合作用是抑制扰动增长，提高流动稳定性。 然后采用染色线流动显示技术与粒子图像测速技术对槽流悬浮流的扰动波特性进行定性和定量观测。染色线观测显示H值增大使扰动失稳距离增加，扰动衰减率与波数的关系同空间模式稳定性分析的理论结果定性一致。PIV测量得到流场速度矢量图及流线图，扰动波幅与波形特征说明，Re数一定时流动稳定性随H值增大而提高。验证了空间模式稳定性分析的理论结果。 从涡量的角度分析纤维改变悬浮流动稳定性的机理，利用涡量输运方程与涡能平衡方程分析纤维的作用。另外比较纤维的平面与三维取向状态、三种封闭格式对稳定性的影响，通过应力将纤维取向分析同流场涡量分析联系起来。 最后应用稳定性分析结果分析槽流悬浮流失稳阶段的减阻特性。发现当波数大于一定值时流动表现出减阻效应，增大H值可提高减阻率。将结果同部分湍流悬浮流减阻的实验结果进行定性比较。分析减阻机理是流速分布曲线及近壁区速度梯度介于层流与湍流之间，H值增大引起壁面剪应力显著下降。更多还原

【Abstract】 Fibre suspensions refer to the liquid or gas flows containing suspending fibre particles. To this day they have been very familiar in nature and many fields of industry. On the other hand, researches of them involve many branches of subjects and have great academic values. This thesis researches on the stability of fibre suspensions applying theoretical, numerical and experimental methods.First the linear stability analysis is performed to fibre suspensions utilizing flow stability, slender-body and orientation tensor theories. The governing equations of channel and pipe suspensions of different stability handling modes and tensor closure approximations are derived. Stability characteristics are obtained through numerical analysis. In general, the influence of fibre additives and their hydrodynamic interactions to the flow results in the increase of critical Reynolds number and the reduction of unstable region of disturbances, therefore reinforces the flow stability.Qualitative and quantitative measurements of disturbances in channel suspensions are carried out using dye emission and PIV techniques. Traces of dyes indicate that the stable length increases with an augment of H, and the relations between spatial attenuation rates of disturbance and wavenumbers are correspondent with theoretical results by the analysis of spatial mode. Diagrams of velocity vectors and streamlines display waveform and amplitude properties, showing the effect of fibres on enhancing the flow stability. The computational results are tested.Finally, the mechanisms behind the instability of fibre suspensions are presented from a point of view of vorticity. Effects of fibres are investigated through equations of vorticity transport and enstrophy balance. Then the two orientation states of fibres and three closure approximations are examined. Analyses of fibre orientation and vorticity in the suspension can be contacted by stress features.In addition, drag reduction characteristics in the transition regime of channel suspensions are studied. It is found that drag reduction occurs with adequate wavenumbers and grows with an increase of H. The mechanisms are revealed through variations of velocity profile and the decrease of wall shear stress.更多还原