湍流相干结构机理研究(Ⅰ)──光滑壁边界层相干结构的物理模型*

本文主要讨论了光滑壁边界层相干结构的特性,建立了这种相干结构的物理模型,从理论上得到慢条宽度、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[3'4'5'7]是相吻合的。     

ON THE MECHANISM OF TURBULENT COHERENT STRUCTURE (I)──THE PYSICAL MODEL OF THE COHERENT STRUCTUREFOR THE SMOOTH BOUNDARY LAYER

In this paper, based on the discussion of properties of the turbulent coherent structure for smooth boundary layer, a physical model has been established. The width of slowly-moving streak line and bursting time of coherent structure expressed by momentum thickness Reynolds number of boundary layer have been obtained, which are in agreement with the experimental data^[3,4,5,7] Project supported by the National Natural Science Foundation of China     

Similarity problem of inceptive cavitation

In the preceding article[1],the relation between thermodynamics condition andinceptive cavitation stage has been discussed.In this paper.we try to introduce thevolume function of inceptive cavitation bubbles.zo(r),instead of the energyequation used in the reference[1],for discussing cavitation similarity problem insimilar flow systems.Under this condition,theoretical result shows that theinception cavitation number K_i increases with a rise of geometry linear scale.Inother words,if two flow systems are kept with similar pattern and liquid,it isimpossible to satisfy the cavitation similarity,This conclusion accords withpractice.     

初生空化状态相似性问题

在前文中[1],讨论了热力学条件与初生空化的关系.在此基础上,引进空泡群的体积函数z₀(r),代替前文中的能量方程式,讨论相似流动体系中的空化状态相似性问题.分析结果表明,在两个满足Froude准则的相似流动体系中,空化状态是不相似的,其初生空化数随几何比尺的增加而增加.理论结果与实践是符合的.     

非牛顿流与浆河及揭底现象

本文利用非牛顿宾汉体的一些性质来解释近年来黄河干支流上出现的浆河及揭底现象。我们认为在宾汉体的两个物理参数中τ_B并不是一个常数,而是弛豫时间极长的一个时间变量。从重力分量和能承受的最大剪切力的对比关系(或流量和τ_B增加率的对比关系),我们就可以解释浆河现象的产生。一般说来,重力分量大于能承受的最大剪切应力τ_B时,宾汉流体就要滑动。而在河底的底坡面并不是相应的河底介质的滑移面时,就会在河底介质土层中产生滑移而产生所谓的揭底现象。      

An analytic solution of dense two-phase flow in a vertical pipeline

According to a mathematical model for dense two-phase flows presented in theprevious paper,a dense two-phase flow in a vertical pipeline is analytically solved,and theanalytic expressions of velocity of each continuous phase and dispersed phase arerespectively derived The results show that when the drag force between two phases dependslinearly on their relative velocity,the relative velocity profile in the pipeline coincides withDarcy’s law except for the thin layer region near the pipeline wall,and that the theoreticalassumptions in the dense two-phase flow theory mentioned are reasonable.     

Expressions for pressure-velocity-gradient correlations

The term for pressure-velocity-gradient correlation was initiated by Rott’srewriting the correlation between the pressure fluctuation gradient and velocity fluctuation.However,it is very difficult to consider the effect of this term.Since Rotta’s work,Launderet al.has made some estimates of this term.In this paper according to the equations forvelocity fluctuation,the pressure fluctuation is solved so that the average value of theproduct of the pressure fluctuation and the velocity fluctuation gradient is obtained.Thus,the whole expressions for the pressure-velocity-gradient correlation are derived.The resultexplains that the limited expressions by Rotta and Launder are reasonable to a certaindegree.The whole expressions in this paper are discussed respectively in two situations:oneis without a separate consideration of large and small vortexes;the other is with a separateconsideration of three kinds of vortexes.Therefore,the paper gives the whole expressions forpressure-velocity-gradient correlation     

Contaminant contraction in two-dimensional oscillatory flows

If the vertically-mixing time is comparable with that of period oscillatory current,the contaminant contraction may occur.The coefficient of shear dispersion is negative(singularity).According to the two-dimensional delay-diffusion equation derived by theauthor:where u(t),v(t)are vertically-averaged velocities,the equations for X(t),Y(t),central displacement,dispersion tensor,had been derived.αD_(ij)/τis positivewhenτis small.If theτis large,the memory functions may be negative.Also theexpressions for D_(ij)and X,Y had been obtained.     

Similar theory and the applicable ranges of one-equation and two-equation models

Here, we are discussing the applicable ranges of one-equation and two-equation turbulence models with the viewpoint of similar theory. The criterions of determining the applicable ranges of these models are given.     

相似理论与应用一方程和三方程模式理论的范围

一般的流体力学工作者,对一方程模式和二方程模式理论的适用范围是并不清楚的.即使是湍流模式理论的工作者,也并不见得对这些理论的适用范围非常清楚.甚至有些时候,算出的结果和实验不相符合也还弄不清楚问题出在那里.本文则是从相似理论的角度来讨论湍流一方程和二方程模式理论的适用范围.给出这些理论能应用的范围的判据.