On the Mechanism of Turbulent Coherent Structure(Ⅰ)──The Physical Model o

ＯＮＴＨＥＭＥＣＨＡＮＩＳＭＯＦＴＵＲＢＵＬＥＮＴＣＯＨＥＲＥＮＴＳＴＲＵＣＴＵＲＥ（Ｉ）──ＴＨＥＰＹＳＩＣＡＬＭＯＤＥＬＯＦＴＨＥＣＯＨＥＲＥＮＴＳＴＲＵＣＴＵＲＥＦＯＲＴＨＥＳＭＯＯＴＨＢＯＵＮＤＡＲＹＬＡＹＥＲＴｓａｉｓｈｕ－ｔａｎｇ（蔡树棠...     

The double velocity correlation function of homogeneous turbulence with constant mean velocity gradient

In this article, as the velocity gradient is taken as a constant value, we obtain the solutions of the equation of fluctuation velocity after Fourier transform. When the mean velocity gradient is small, they represent the picture of eddies, of which the homogeneous turbulence (both isotropic and nonisotropic) of the final period is composed. By using the eddies of these types at different times, we may compose the steady turbulent field with the constant velocity gradient and this field may represent the turbulent field in the central part of the channel flow or pipe flow approximately. Then we may obtain the double velocity correlation function of this turbulent field, which involves both longitudinal correlation coefficient and the transversal correlation coefficient . We compare these theoretical coefficients with the experimental data of these coefficients at initial period and final period of isotropic homogeneous turbulence. And then we obtain the relationship between the turbulent double velocity correlation coefficient and the mean velocity gradient. Finally, we get the expressions of the Reynolds stress and the eddy viscosity coefficient.     

常数速度梯度时均匀湍流的二元速度关联函数

在湍流脉动速度比较小的条件下,本文得到了富氏变换过后脉动速度方程的解.它所代表的涡旋,在平均速度梯度为小量时,化为具有常数平均速度梯度的、组成后期均匀各向同性湍流场的涡旋和组成后期各向异性湍流场的涡旋.利用不同时刻的这种涡旋解,组成定常的有常数平均速度梯度的湍流场,这个湍流场可以近似地表达槽流和管流近中心区域的湍流场.我们求得了这种湍流场的二元速度关联函数,包括纵向的关联系数f(γ/λ)和横向的关联系数g(γ/λ).并且和均匀各向同性湍流实验中的前期和后期的f(γ/λ)和g(γ/λ)进行了比较.并且弄清楚了速度梯度对关联系数f(γ/λ)所产生的影响,最后还得到了雷诺应力和涡旋粘性系数的表达式.     

THE SEPARATION OF LARGE VORTEXES AND THE CLOSED EQUATIONS OF TURBULENCE MODEL

This paper presents a new kind of average for the locally-generated large vortexes sothat the physical quantities of the locally-generated large vortexes and the external largevoriexes can be rigorously separated from the equations for the large vortexes proposed in aprevlous paper.To the equations the two kinds of large vertexes.some auxiliaryrelations are introduced,and the value of the length-scale l_N of energy dissipation of theexternal large vortexes may be determined according to the actual circumstances of thedisturbance of external sources.Thus,the resulting equations of second moments ofturbulent velocity fluctuations for the two kinds of large vortexes can be made closed.Meanwhile,the corresponding coefficients of diffusion in the previous paper areimproved.Finally,a closed set of numerically-solvable equations of turbulence model areobtained.     

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 slurryare different from that of ordinary Newtonian fluid,and can be describedby that of Bingham fluid.Hence its shearing stress should be described bythe formula of the shearing stress of Bingham fluid.But the author holdsthe contrary opinion and firmly believes that the slurry is a highly viscousfluid with very long relaxation time such as those of asphalt,glass,etc.In this article,we have discussed the mechanical properties of the slurryand the reslstance of a sphere moving with uniform veloclty in the slurry.In the process of discussion.we use Stokes solution of the vlscous fluidpassing around a sphere.When the sphere is in equilibrium under theaction of gravitational force,the force of buoyancy and the resistance,we get the velocity of sedimentation.When the velocity of sedimentationis equal to zero,we get the relation between the yield stress of Binghamfluid and the diameter of the particles which will not sink.The theoreticalresults     

二元渠道中泥沙的输移和渠底的改变

研究泥沙運動是對我國國民經濟有很重要意義的工作。過去有很多实测,实验和理論研究工作,但都没有能够很清楚地說明輪沙机构和解决一些爭論的問題。本文從流體力學的观點,首先对懸沙,底沙和中間過渡類型的泥沙加以區分,然後再按照這樣的區分来建立一個簡單的模型圖案。根據這一個模型圖案和流體力學的基礎理論,我們建立了一個自己封閉的方程组來確定速度,水深,含沙濃度等未知的流體力學量。這方程組中的每一個方程式在和已有的实驗結果比較時候,人致都能够符合得很好,接着我們根據这些方程式,得到两个水流相似的必要和充分條件。最後我們对用這些方程式計算流速和水深以及設計不淤渠道给出了计算的方法,為了能把每一步驟所需要的經驗常數更好的肯定下來,我們建議做一系列有系統的精密實驗來作出計算所需要的图表。     

FUNDAMENTAL EQUATIONS OF TURBULENT TWO-PHASE FLOW

A new set of Keynolds equations for predicting turbutent two-phase flows has beendeveloped by means of Reynolds averaging method on the unsteady laminar equations oftwo-phase flow.These equations involve average terms of products of turbulent fluctuationsin some physical parameters in a large degree.The interaction forces between two phases,thepressures for dispersed phase,extra stresses except for pressure and the expressions forenergy interchange between two phases have been discussed.     

泥沙在静水中的沉淀运动——(Ⅱ)沉速在时间过程里的变化

一.引言 在工程上一般碰到泥沙在水中运动的时侯,都应用斯托克斯公式来计算泥沙所受到的阻力。但是斯托克斯公式是一个圆球在无穷的粘性流体中作匀速运动时的阻力定律,对于很多砂子同时下沉作非匀速运动时,斯托克斯公式显然不能应用。本文根据了流体力学在小瑞诺数情况下的理论来讨论比较稀薄的泥沙在静水中的非匀速的沉淀问题。     

裂缝的张开位移和应变的关系

本文采用Kármán-钱处理亚音速流动方法的精神。处理了弹塑性断裂力学问题.通过建立的“双弹性”模型,从理论上得到了裂缝端部的张开位移和应变的方程组.实例计算结果表明,理论值全部落在实验结果的分散带内.文中并从理论上解释了实验结果与材料的性质及实验条件的关系.本文的结果不仅为宽板实验所证实,也被文献[2]的实验所证实.同时也表明。公式(37)用于工程,能够分析压力容器上应变裂缝的容许极限.     

ON THE MECHANISM OF TURBULENT COHERENT STRUCTURE（II）──A PHYSICAL MODEL OF COHERENT STRUCTURE FOR THE ROUGH BOUNDARY LAYER

（刘宇陆）（蔡树棠）ＯＮＴＨＥＭＥＣＨＡＮＩＳＭＯＦＴＵＲＢＵＬＥＮＴＣＯＨＥＲＥＮＴＳＴＲＵＣＴＵＲＥ（ＩＩ）──ＡＰＨＹＳＩＣＡＬＭＯＤＥＬＯＦＣＯＨＥＲＥＮＴＳＴＲＵＣＴＵＲＥＦＯＲＴＨＥＲＯＵＧＨＢＯＵＮＤＡＲＹＬＡＹＥＲ￥ＬｉｕＹｕｌｕ；Ｃ...