Structure of turbulent pipe flow

The problem of turbulent flow in a straight circular pipe is solved. We consider a system consisting of the equation of motion, the equation for the turbulence energy, the expression relating the turbulence coefficient with the turbulence scale, and the integral formula for determining the turbulence scale. A numerical solution is presented for this closed system of equations for turbulent flow. The results of calculations are compared with experimental data.     

爆破振动速度预测安全保证系数的确定

基于爆破振动速度预测公式回归分析的基本原理,提出根据建筑物不同安全等级应选择一定的可靠性指标,并推导了预测爆破振动速度公式中所含安全保证系数的计算过程。为简化计算过程,又进一步提出了基于监测数据量、回归分析相关系数以及可靠性指标的关于安全保证系数计算的经验公式。经过大量监测数据验证了该经验公式的计算精度和可靠性均能满足工程实际需要,从而修正了萨氏公式预测精确度不够的缺陷,可为重要建筑物周边的安全爆破设计提供参考。     

剪切湍流的涡黏张量模式

对剪切湍流提出了涡黏系数为四阶张量的涡黏张量模式。引入近代数学中Ｍｏｏｒｅ－Ｐｅｎｒｏｓｅ广义逆矩阵的研究结果，给出了构造涡黏张量各分量的计算公式。用平面后台阶流动验算了剪切湍流的涡黏张量模式，比ＲＳＭ和ｋ－ε模式更接近实验结果。提出了剪切湍流涡黏张量模式的应用设想。     

Short-and resonant-range interactions between scales in turbulence and their applications

Interactions between different scales in turbulence were studied starting from the incompressible Navier-Stokes equations. The integral and differential formulae of the shortrange viscous stresses, which express the short-range interactions between contiguous scales in turbulence, were given. A concept of the resonant-range interactions between extreme contiguous scales was introduced and the differential formula of the resonant-range viscous stresses was obtained. The short- and resonant-range viscous stresses were applied to deduce the large-eddy simulation ( LES ) equations as well as the multiscale equations, which are approximately closed and do not contain any empirical constants or relations. The properties and advantages of using the multiscale equations to compute turbulent flows were discussed. The short-range character of the interactions between the scales in turbulence means that the multiscale simulation is a very valuable technique for the calculation of turbulent flows. A few numerical examples were also given.     

Momentum and heat transfer in two-phase bubble flow—I. Theory

A theory is proposed which describes the transfer process of momentum and heat in a two-phase bubble flow in channels. The eddy diffusivity to express the turbulent structure of the liquid phase is subdivided into the two components, one for the inherent wall turbulence independent of bubble agitation and the other for the additional turbulence caused by bubbles. On the basis of the theory, the velocity profile and the frictional pressure gradient for a given flow can be predicted when its void fraction profile is known. Furthermore, when a uniform heat flux is added to the system, its temperature distribution and heat transfer coefficient can be determined. A method for the numerical calculation of these parameters is also presented.     

船舶水润滑尾轴承当量半径等效计算及其摩擦学性能研究

水润滑尾轴承摩擦磨损性能是影响船舶工作性能的主要因素之一,合理预测水润滑尾轴承工作过程中的摩擦系数对其性能评估具有重要意义.目前对于水润滑尾轴承摩擦系数的理论计算公式已经存在.但由于销盘试验下无法有效获取当量半径,公式在销盘试验条件下的实用性不佳.对此在总结了边界润滑条件下,水润滑尾轴承摩擦机理的基础上,通过在CBZ-1销盘试验机上进行大量试验来进行当量半径等效参数计算公式的总结与摩擦系数经验公式的验证.研究结果表明:(a)在使用理论摩擦系数计算公式的前提下,当量半径等效参数公式拟合合理,具备较高准确性;(b)试验材料的理论摩擦系数与实际摩擦系数误差较小,为同类型试验摩擦性能研究提供了理论与试验基础;(c)水润滑尾轴承材料在工作过程中的摩擦力来源主要分为滞后摩擦力、犁沟摩擦力以及黏着摩擦力.当其处于边界润滑状态下时,滞后摩擦力为主要的摩擦力来源.该研究为水润滑尾轴承的等效当量半径在销盘试验条件下的应用提供了试验基础.     

支环对钢丝绳绳圈张力系数的影响

本文研究了提升机卷筒中间支环对钢丝绳绳圈张力系数的影响，从能量角度提出了计算原则，导出计算钢丝绳绳圈张力系数的公式．     

对MM-200型磨损试验机摩擦系数计算公式的修正

对ＭＭ－２００型磨损试验机摩擦系数计算公式重新进行了推导和计算,所得公式与原公式相比可降低求解摩擦系数时的误差．原公式在试环与试块之间的接触角增大时,误差也随之增大,使得试验数据的可靠性和可比性严重降低,因此必须对原计算公式进行修正．     

Comparison of methods to estimate the scour downstream of a ski jump

This study analyzes the expected depth and scour shape in the Toachi River (Ecuador) as a result of the construction of the Toachi Dam in order to avoid problems with progressive scour. The dam has a maximum height of 59 m to the foundations. The free surface weir ends in a ski jump and has been designed to operate with a peak discharge of 1213 m³/s. As each method has its limitations, the scour is studied with four complementary procedures: 1) a 1:50 Froude scale similitude laboratory model used as validation case; 2) 36 empirical formulae derived from models and prototypes; 3) a semi-empirical methodology based on pressure fluctuations-erodibility index; and 4) FLOW-3D numerical simulations. The expected scour depth is 6.65 m for the design flow. The results are close to the physical model. In the numerical analysis, turbulence is treated using the three RANS approaches. The choice of the turbulence model and the bed load coefficient in the Meyer-Peter & Müller formula are of great importance. The best results were obtained using the RNG k-ε turbulence model and a bed load coefficient below 7.     

Development of lattice turbulence in a stream with a constant velocity gradient

On the basis of the equations for the Reynolds stresses and the equation for the scale of the turbulence, an analysis is made of the development of lattice turbulence in a stream with a constant velocity gradient. The constants in the equations are determined under the assumption that, far from the lattice and with large Reynolds numbers, the structure of the turbulence tends toward a limiting state with constant values of the correlation coefficient, the degree of anisotropy, and the dimensionless velocity gradient. The constants in terms containing the viscosity are determined from a consideration of the flow beyond the lattice without a velocity gradient in the final stage of decay of the turbulence. The equations obtained were solved in an electronic computer. The calculation is in satisfactory agreement with the existing experimental data. For calculating flows with a variable velocity gradient, instead of the equation of the scale, it is proposed to use an equation for the frequency of the turbulent pulsations obtained in the present work. The computer calculations were made by S. I. Bekritskaya.     

LDA在减压箱空化特性试验研究中的应用

本文用新型的光纤激光测速仪(Fibrc-Optic LDA)对减压箱内闸墩附近紊动流场的空化特性进行了测试研究.结果表明:只有采用断面上各点流速的统计平均值作为参考断面的平均流速才能保证足够的精度;速度效应对空化初生的影响可不考虑,但紊流强度的变化对其影响却不容忽视。文中将不同尺寸闸墩的流速系数用统一经验公式表达,发现流速系数的变化与紊流强度密切相关,由此得出的紊流强度随流速而变化的曲线与实测值符合较好。本文还对 LDA 在类似减压箱的流场应用提出了几点体会和建议。     

考虑梗腋影响的波形钢腹板组合箱梁剪力滞效应研究

考虑梗腋在波形钢腹板组合箱梁剪力滞效应的影响,通过剪力流公式定义了考虑梗腋影响的修正系数,运用变分法得到对应的微分方程,然后求出简支波形钢腹板组合箱梁在集中荷载作用下的剪力滞系数计算公式,采用数值模拟进行对比验证。最后通过调整梗腋尺寸参数,研究梗腋形状变化对剪力滞效应的影响。结果表明,考虑梗腋影响后的理论计算结果与有限元结果吻合较好;波形钢腹板组合箱梁的剪力滞效应现象随着梗腋影响系数的增大而减小;考虑梗腋影响的波形钢腹板组合箱梁剪力滞系数较未考虑情况大幅度降低,在集中荷载下剪力滞效应系数减小约10%;当梗腋宽度与上翼板宽度的比值大于0.5时,对剪力滞效应的影响变化较小,梗腋高度为其宽度的0.16~0.19倍时对剪力滞效应影响最大。     

直流磁场下销盘摩擦过程中的电磁感应力矩分析

为了研究磁场对材料摩擦磨损性能的影响,本文分析了直流磁场下销盘摩擦过程中的涡流和电磁感应力,并通过积分得到感应力矩的计算公式.在销盘0.1 mm间隙时检测了磁吸力和在不同试验条件下盘试样所受的感应力矩,利用试验数据对感应力矩公式中的修正系数进行了最小二乘法拟合,所得感应力矩公式的计算结果与不同电流和转速下的试验数据很好地吻合.在摩擦磨损过程中,可利用感应力矩公式计算出相应试验条件下盘所受的感应力矩,分析其对摩擦系数的影响.     

Influence of turbulence intensity and free stream velocity oscillations on stagnation point heat transfer

A model is proposed for the momentum eddy diffusivity induced by free stream turbulence intensity and integral length scale. The eddy diffusivity model is applied to the stagnation point of a cylinder situated in a steady uniform crossflow in the presence of free stream turbulence. A numerical solution of the governing steady-state momentum and energy equations with the proposed eddy diffusivity model yielded results for the skin friction coefficient and the Nusselt number. Agreement between the numerical predictions of this work and experimental data is very good. The experimental data concerning the unsteady stagnation point heat transfer under the combined influence of free stream velocity oscillations and turbulence intensity have been successfully correlated by means of a new turbulence parameter     

EFFECT OF EMPIRICAL COEFFICIENTS ON SIMULATION IN TWO-SCALE SECOND-ORDER MOMENT PARTICLE-PHASE TURBULENCE MODEL

A two-scale second-order moment two-phase turbulence model accounting for inter-particle collision is developed, based on the concept of particle large-scale fluctuation due to turbulence and particle small-scale fluctuation due to collision. The proposed model is used to simulate gas-particle downer reactor flows. The computational results of both particle volume fraction and mean velocity are in agreement with the experimental results. After analyzing effects of empirical coefficient on prediction results, we can come to a conclusion that, inside the limit range of empirical coefficient, the predictions do not reveal a large sensitivity to the empirical coefficient in the downer reactor, but a relatively great change of the constants has important effect on the prediction.     

基于组件法的穿心螺栓连接CFST柱节点初始刚度计算

本文基于EC3中的组件法,分析并建立了不同类型穿心螺栓连接CFST柱节点的力学模型,提出了EC3中未涉及的加强角钢的组件模型以及穿心螺栓连接刚度系数计算公式,推导了不同节点的初始刚度计算公式,试验结果和公式结果的对比表明,采用EC3给出的受拉螺栓刚度系数将大大低估穿心螺栓连接CFST柱节点的初始转动刚度,而采用本文所提出的考虑穿心螺栓预紧力的受拉螺栓刚度系数计算公式则与试验结果吻合较好．     

A method of calculating the energy spectral density of homogeneous isotropic turbulence

A numerical method is described which can be used to calculate the development downstream (or in time) of the energy spectral density distribution (over the modulus of the wave-number vector) of homogeneous isotropic turbulence in the entire wave-number range. The effect of the step in the modulus of the wave-number vector on the accuracy of the calculation is investigated. The results of a calculation of the process of degeneration of homogeneous isotropic turbulence are presented along with some integral characteristics of the spectrum. The results of the calculation are compared with experiment.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 1, pp. 13–19, January–February, 1978     

So-called constants of turbulence in rough pipes

A direct analysis of Nikuradse's experiments on flow in rough pipes has shown that on the quadratic resistance interval the value of the second constant of turbulence depends on the relative roughness of the pipe. It is established that the universal logarithmic relation for the velocity profile in a pipe in the quadratic resistance regime is an approximation of the more accurate relation obtained by the authors, which takes into account the effect of the relative roughness of the pipe. Where the roughness is significant, the proposed expression for the skin-friction coefficient is more accurate than the well-known Prandtl-Nikuradse formula.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 2, pp. 182–185, March–April, 1990.     

船舶应急抛锚计算方法研究

应用常规经验公式和有限元CEL大变形计算方法,结合抛锚试验,研究了上海LNG管道项目北港5 wt级船舶8.3 t船锚、南港40 wt级船舶18.80 t船锚在BSZ111等多个钻孔点的应急抛锚贯入深度情况,其中CEL方法还考虑了正面贯入、窄面斜向贯入和宽面斜向贯入情况．公式法计算的应急抛锚最大贯入深度北港为2.60 m,南港为3.13 m,而有限元CEL大变形计算方法得出北港为2.86 m,南港为5.24 m．结果表明：CEL方法计算所得窄边(60°)贯入深度普遍大于经验公式计算所得值,说明横截面积的变化是影响贯入深度计算的重要因素．公式法的结果受到土壤系数恒定不变因素的限制,无法考虑贯入过程中土壤的竖向和横向刚度的变化,结果相对偏小,而CEL法可考虑多层土壤刚度以及土壤刚度随土层变形增加后的折减,计算过程更为客观,结果偏于安全考虑,适合作为设计依据．所以,对土层组成相对单一时可采用公式法,而对土层组成多变的复杂情况,建议采用更加客观和安全的CEL方法．     

A stability condition for turbulence model: From EMMS model to EMMS-based turbulence model

The closure problem of turbulence is still a challenging issue in turbulence modeling. In this work, a stability condition is used to close turbulence. Specifically, we regard single-phase flow as a mixture of turbulent and non-turbulent fluids, separating the structure of turbulence. Subsequently, according to the picture of the turbulent eddy cascade, the energy contained in turbulent flow is decomposed into different parts and then quantified. A turbulence stability condition, similar to the principle of the energy-minimization multi-scale (EMMS) model for gas–solid systems, is formulated to close the dynamic constraint equations of turbulence, allowing the inhomogeneous structural parameters of turbulence to be optimized. We name this model as the “EMMS-based turbulence model”, and use it to construct the corresponding turbulent viscosity coefficient. To validate the EMMS-based turbulence model, it is used to simulate two classical benchmark problems, lid-driven cavity flow and turbulent flow with forced convection in an empty room. The numerical results show that the EMMS-based turbulence model improves the accuracy of turbulence modeling due to it considers the principle of compromise in competition between viscosity and inertia.