The mechanical properties of the slurry and the resistance force of a sphere moving with uniform velocity in the slurry

It is commonly considered that the mechanical properties of the slurry are different from that of ordinary Newtonian fluid, and can be described by that of Bingham fluid. Hence its shearing stress should be described by the formula of the shearing stress of Bingham fluid. But the author holds the contrary opinion and firmly believes that the slurry is a highly viscous fluid with very long relaxation time such as those of asphalt, glass, etc. In this article, we have discussed the mechanical properties of the slurry and the resistance of a sphere moving with uniform velocity in the slurry. In the process of discussion, we use Stokes solution of the viscous fluid passing around a sphere. When the sphere is in equilibrium under the action of gravitational force, the force of buoyancy and the resistance, we get the velocity of sedimentation. When the velocity of sedimentation is equal to zero, we get the relation between the yield stress of Bingham fluid and the diameter of the particles which will not sink. The theoretical results calculated are compared with the experimental data of Northwest Institute of Hydrotechnical Research and Institute of Hydraulic Research, Yellow River Conservancy Commission. They are congruous.     

湍流相干结构的机理研究(Ⅱ)─粗糙壁边界层相干结构的物理模型*

本文主要分析了粗糙壁面相干结构的特性以及与光滑壁面相干结构的区别,讨论了从光滑壁到粗糙壁过渡的问题,在此基础上建立了粗糙壁面相干结构的物理模型,从理论上得到了慢条宽度、猝发时间等物理量与动量厚度雷诺数的关系,其结果与实验结果是相符合的.     

垂直管道中密相两相流动的解析解

本文依据文献[1]的密相两相流动的数学模型,对垂直圆管中密相两相流动进行了解析求解,分别得到了连续相和分散相的速度解析表达式.在相间阻力与相间速度差成比例时,除了在离管壁面很近的薄区之外,管道流动规律与达西渗流定律完全一致.本文验证了文献[1]的密相两相流动数学模型的假定在本文情形下是合理的.     

气固两相流和气液两相流的掺混问题

在工业生产中气固两相流和气液两相流的掺混是一个常见问题.在这个掺混流动过程中,颗粒团将形成,且在颗粒碰撞聚结效应和分裂效应相平衡时,颗粒团将具有稳定半径.本文引入了颗粒团线尺度数密度分布函数n(a,,t),从分子运动论的观点出发,导出了颗粒团线尺度数密度分布函数的控制方程.最后,在气相流速非常缓慢的情况下,得到了颗粒团平均稳定半径的表达式.     

大小涡旋分开考虑的模式理论

近年来,k-ε模式普遍流行,但它是一种梯度形式的模式理论。由于湍流涡旋的衰减时间极长,在一般的流动问题中,上游产生的大涡旋或附近产生的大涡旋在到达当地时还远远没有衰减掉,因此会对当地的流动产生很大的影响。根据不可逆热力学理论的基本原理,必须准平衡、准定常和小偏离的情形下,才能使用梯度形式的流和力的关系式。一般说来这对大涡旋是并不满足的,所以k-ε模式的应用有着很大的局限性。本文根据湍流的实际情况,把湍流脉动分成大涡旋和小涡旋两个组成部份,并且把大涡旋部份再分成局部产生的和上游流来或扩散过来的两个组成部份,这样就得到了由三个部份组成的湍流模式理论。     

THE THEORY OF SIMILARITY AND THE PROFILE OF VERTICAL DISTRIBUTION OF CONCENTRATION OF SAND PARTICLES

In this article,we treat the problem of two-dimensionaluniform steady channel flow of turbid water with theory ofsimilarity.Under the condition of similarity of turbulentfluctuation velocity and fluctuation of concentration ofsand particles,we obtain the profile of the vertical dis-tribution of concentration of sand particles.This profileof vertical distribution of concentration of sand particlesis slightly different from that obtained by diffusion theory,and departs from that obtained by gravitational theory.     

THE DOUBLE VELOCITY CORRELATION FUNCTION OF HOMOGENEOUS TURBULENCE WITH CONSTANT MEAN VELOCITY GRADIENT

In this article,as the velocity gradient is taken as a con-stant value.we obtain the solutions of the equation of fluc-tuation velocity after Fourier transform.when the mean velo-city gradient is small,they represent the picture of eddies,of which the homogeneous turbulence(both isotropic and non-isotropic)of the final period is composed.By using theeddies of these types at different times,we may compose thesteady turbulent field with the constant velocity gradientand this field may represent the turbulent field in thecentral part of the channel flow or pipe flow approximately.Then we may obtain the double velocity correlation functionof this turbulent field,which involves both longitudinalcorrelation coefficient f(r/λ)and the transversal correlationcoefficient g(r/λ).We compare these theoretical coefficientswith the experimental data of these coefficients at initialperiod and final period of isotropic homogeneous turbulence.And then we obtain the relationship between the turbulentdouble velocity corr     

THE MIXING OF GAS-LIQUID FLOW WITH VAPOR AND GAS-SOLID FLOW

In the industrial production,the mixing of gas-liquid flow with vapor and gas-solidflow is a very common problem.In the process of the mixing,solid particle-clusters willform,and will have steady radii when the effect of the gathering of particles is balanced withthat of the breaking of particle-clusters.Then,the population distribution functionn(a,(?)t)of size of particles per unit length per unit volume is introduced,and its governingequation is derived on the analogy of the molecular kinetic theory.Finally,when the gasflow is very slow,the expression of steady average radius of particle-clusters is obtained.