弯道水流二维浅水模型的修正研究

借鉴有关弯道水流流速分布的研究成果,计入深度平均流速与真实流流速分布差值引起的扩散效应,在正交曲线坐标系下建立了平面二维浅水模型.采用以标准κ-ε模型为基础的曲率效应修正紊流模型模拟紊动应力项,在一定程度上考虑了流线弯曲水流紊动应力的各向异性.应用控制体积法和交错网格法离散方程,并用SIMPLEC算法求解离散方程;同时采用修正后的模型对90°弯道水流进行了数值模拟,并与原模型的计算结果及实测资料进行了比较,结果表明该模型能够有效地模拟流线弯曲水流的水力特性.     

曲线坐标系下平面二维浅水模型的修正与应用

借鉴有关弯道水流流速分布的研究成果,计入弯道环流引起的横向的动量交换,对曲线坐标系平面二维浅水方程做了修正;采用边界处正交的曲线网格生成技术,处理复杂的计算区域边界。采用修正后的模型对90°弯道水流进行了数值模拟,并与原模型的计算结果及实测资料进行了比较,结果表明该模型能够有效地模拟流线弯曲的复杂水流的水力特性。     

连续弯道水流紊动特性试验研究

采用电磁流速仪, 在接近天然河道形态的连续弯道中, 对沿程断面上各点的脉动流速进行量测.根据测得的数据分析得到了紊动能谱、紊动强 度、紊动切应力、紊动能、紊动参数等的全断面分布.研究结果表明水流紊动主要集中在10 Hz以下,不同环流形式与各种紊动量之间会互相影响,边壁处纵向紊动强烈、横向和垂向紊动较弱.     

基于CFD的河流弯道二次流的三维数值模拟

为了系统地研究河流弯道在二次流影响下水沙运动的特点,本文基于CFD(Computational Fluid Dynamics)数值模拟和物理模型实验的方法,对河流弯道二次流进行了模拟和测量;应用雷诺时均法模型,结合Eulerian两相流模型对河流弯道二次流及其泥沙冲淤规律进行了数值模拟;以SIMPLE方法对压力场和速度场进行了耦合计算,并对辽宁省阜新市细河某段支流河道进行了物理模型实验,数值模拟的结果与实验结果基本一致,表明了本文方法的正确性。在此基础上,对90°弯曲的梯形断面河道的二次流结构和冲淤变化进行了分析,为防洪和水利设施的建设提供理论依据。     

正交数值网格的生成及平面二维流场的数值模拟

提出了一种边界正交曲线网格的生成方法。在内域,求解拉普拉斯方程组生成二维正交曲线网格;在计算域边界,提出了正交曲线网格边界正交化处理的分段拉格朗日插值边界滑动法,并对控制方程N-S方程进行曲线坐标变换,使用SIMPLEC算法求解曲线坐标下的k-ε双方程湍流模型。文中以长江重庆九龙坡弯道河段正态模型为资料进行验证,计算了流场,数值模拟结果与实测结果吻合较好。     

河型发育过程的二维数值模拟研究

改进已有二维平面水沙模型,进一步考虑河床粗化、弯道二次流及河床结构对泥沙输运的影响;并针对河湾形态对崩岸的影响提出新的非粘性土崩岸模拟方法,使其能模拟边滩的形成。利用改进后模型分别对Yen弯道水槽泥沙冲淤试验及Friendkin室内弯曲小河塑造试验进行模拟;模拟结果与试验观测资料吻合较好,表明考虑弯道对泥沙输运及河岸崩塌影响的模型能够更准确反映天然河流演化过程,为研究河型演化机理及各控制因素变化规律提供新手段。     

柱状颗粒在线性剪切流场中运动的数值模拟研究

柱状颗粒是自然界和工业过程中一种普遍的颗粒形状,它在流场中的运动与球状颗粒有显著区别.论文基于直接力浸入边界法数值模拟了柱状颗粒在线性剪切流中的运动;分析了柱状颗粒周围流场参数分布,获得了作用在颗粒上的力矩变化,明确了由流体曳力和颗粒惯性力相互作用导致颗粒运动的速度和角速度的变化规律,同时考虑了颗粒雷诺数对颗粒运动的影...     

定床弯道内水沙两相运动的数值模拟

在适体同位网格中采用非正交曲线坐标系下的三维k-ε-kp固液两相双流体湍流模型研究弯道内水流和悬浮泥沙运动,主要计算了试验室S型水槽内清水流动的三维流场、120°弯道内水沙两相流动中底沙与底流的运动轨迹以及S型水槽内水沙两相流动的两相流场和泥沙浓度场. 对于S型水槽内清水流动,数值结果与试验结果吻合良好. 120°弯道内水沙两相流动中固液两相的运动轨迹在弯道直线段基本重合,在弯道内泥沙轨迹逐步偏离水体轨迹,其偏离程度随泥沙粒径增大而增大. 从S型水槽内水沙两相流动计算结果中发现泥沙纵向流速在壁面附近比水流纵向速度大,在远离壁面区域比水流纵向速度小;弯道内泥沙横向流速比水流横向流速小;垂向流速在直线段和泥沙沉速相当,在弯道内受螺旋水流影响而变化;两相流速差别随泥沙粒径增大而变大;泥沙浓度呈现下浓上稀的分布,在弯道内横向断面上呈现凸岸大凹岸小的分布,泥沙浓度随泥沙粒径增大而减小.      

二次燃烧对底排装置尾部流场影响的数值模拟

为研究二次燃烧对底排尾部流场的影响,建立了底排装置尾部流场的化学非平衡流数学物理模型。其中二次燃烧模型采用10组分25步反应的H₂-CO燃烧模型,运用统一算法的思路编程求解二维轴对称方程组。数值模拟结果与实验结果较吻合。在此基础上,对尾部流场以及燃烧特性进行了数值预测, 结果表明:二次燃烧所释放的热能远大于排气本身的热能,对增压减阻的贡献可达78%。二次燃烧改变了尾部的温度分布规律,使温度峰值分布在两个回流区内。排气沿着两回流区间的狭缝流入剪切层发生燃烧。一部分混气回流入底部附近,其中氧气不充足,存在大量CO和少量H₂未直接反应。一部分混气沿着剪切层流入下游以及主回流区内,氧含量逐渐增多,H₂和CO被反应殆尽。结果可为进一步研究底排增压减阻提供参考。     

N表面张力对近固壁二空化泡影响的数值研究

在忽略浮力下，用边界积分方法数值模拟了表面张力对固壁之上且靠近固壁的二轴对称空化泡生长和溃灭的影响，发现在下空泡最大等效半径为上空泡一半情形，若固壁对下空泡的Bjerknes力大于上空泡对下空泡的Bjerknes力，则表面张力的作用将使下空泡溃灭加速，使其向下的液体射流变强变宽；若固壁对下空泡的Bjerknes力小于上空泡对下空泡的Bjerknes力，则表面张力的作用将使下空泡溃灭变慢，使其向上射流变弱变细长；若这两个Bjerknes力近于相等，则表面张力将会对下空泡溃灭有重大作用，如改变下空泡射流的方向甚至形式(如由环状变向下或由向上变环状)，当上空泡等于或小于下空泡时，表面张力将不会对这两个空泡的行为产生显著影响，定性地分析了表面张力作用的机理。     

二层密度分层流体重力流的数值模拟

从RANS方程和RNGk-ε湍流模型出发,采用流体体积法(VOF)来模拟密度分层流动,对盐水和淡水因密度差异导致的分层重力流动现象进行了数值模拟.文中报道了平底水槽重力流、狭孔交换流的数值模拟结果,分层重力流锋面运动速度的计算值与现有的半理论半经验公式一致.为了揭示地形变化对分层重力流的影响,对设有缓变潜堤的水槽内分层重力流动的形成过程进行了数值模拟,给出了重力头推进速度和局部流场的计算结果,并讨论了分层流界面、流量和锋面附近的流速分布特征.     

机动弹头高超声速粘性绕流数值模拟

采用空间二阶精度的交替方向隐式分解的NND格式求解完全气体假定下的非定常薄层近似NaVierStokes方程,并采用抛物化的椭圆型方程生成复杂带翼弹头的空间网格.最后给出了机动弹头在M∞=7.3,α=20°下的流场计算结果.计算结果表明本文所采用的计算网格及计算方法可以适用于高超声速复杂流场的数值模拟.     

Numerical analysis of turbulent flow in a rotating U-bend with roughened walls

A numerical analysis has been performed for a developing turbulent flow in a rotating U-bend of strong curvature with rib-roughened walls using an anisotropic turbulent model. In this calculation, an algebraic Reynolds stress model is used to precisely predict Reynolds stresses, and a boundary-fitted coordinate system is introduced as a method of coordinate transformation to set the exact boundary conditions along the complicated shape of U-bend with rib-roughened walls. Calculated results for mean velocity and Reynolds stresses are compared to the experimental data in order to validate the proposed numerical method and the algebraic Reynolds stress model. Although agreement is certainly not perfect in all details, the present method can predict characteristic velocity profiles and reproduce the separated flow generated near the outer wall, which is located just downstream of the curved duct. The Reynolds stresses predicted by the proposed turbulent model agree well with the experimental data, except in regions of flow separation.     

Study of the effect of the non-orthogonality for non-staggered grids—the theory

An investigation has been conducted to determine the effect of the grid non-orthogonality on the convergence behavior of two-dimensional lid-driven cavity flows. The relevant theory is presented in this article. In the present work, the contravariant velocity fluxes are used as the dependent variables on non-orthogonal, non-staggered grids. The momentum equations retain a strongly conservative form. Two practices for treating the momentum interpolation method in general curvilinear co-ordinates are presented. In each practice, the momentum interpolation formulations with and without velocity underrelaxation factor are considered. The discretization equations are solved using the SIMPLE, SIMPLEC and SIMPLER algorithms. © 1998 John Wiley & Sons, Ltd.     

The 3D Transition to Turbulence in Wake Flows by Means of Direct Numerical Simulation

The three-dimensional transition to turbulence in flows around bodies of non-rectangular configuration has been analysed physically by performing direct numerical simulation to solve the system of Navier-Stokes equations. The successive stages of 3D transition, beyond the first bifurcation, have been detected first in the incompressible regime, for a circular cylinder configuration. The generation of streamwise vorticity, organised according to spanwise periodic cells has been associated with the development of large-scale coherent spanwise undulations of the originally rectilinear (nominally 2D) alternating vortex rows. The wavelengths of these undulations have been determined as a function of Reynolds number. As this parameter increases, a further inherent change of the flow transition is obtained and analysed, the natural vortex dislocations pattern. Beyond this change, the increase of Reynolds number yields an abrupt shortening of the spanwise wavelength and the flow undergoes another transition step, whose critical Reynolds number is evaluated by the present DNS approach in association with the Ginzburg-Landau model. Therefore, the linear and non-linear parts of the flow transition have been quantified by means of the amplitude evolution versus time obtained by the present DNS, in conjunction with the mentioned global oscillator model. This revised version was published online in July 2006 with corrections to the Cover Date.     

采用NND方法计算三维喷管气流场

本文运用NND显式差分格式,计算了三维喷管气流场。气流场计算的基本方程为一般贴体坐标系下三维守恒型的欧拉方程。采用了时间分裂法和Steger-Warming矢通量分裂技术。在喷管内沿周向的每个由轴线和壁面构成的子午面上根据泊松方程生成贴体网格。本文运用三维程序计算了轴对称JPL喷管,同时与实验结果和前人采用轴对称二维程序所计算的结果做了对比。最后,本文还计算了三维矢量喷管,计算结果与现有的实验结果一致。通过轴对称JPL喷管和三维矢量喷管的计算考核,表明建立的算法和编写的计算程序是正确的。文中提出了采用子午面形式的贴体网格时奇性轴的处理方法。计算结果表明在喷管壁面处,马赫数与压强的计算结果与实验值吻合较好,而在喷管轴线处,只有当网格较密时,才能得出与实验结果接近的计算结果。     

Two‐dimensional modeling for stability analysis of two‐phase stratified flow

The effect of wavelength and relative velocity on the disturbed interface of two‐phase stratified regime is modeled and discussed. To analyze the stability, a small perturbation is imposed on the interface. Growth or decline of the disturbed wave, relative velocity, and surface tension with respect to time will be discussed numerically. Newly developed scheme applied to a two‐dimensional flow field and the governing Navier–Stokes equations in laminar regime are solved. Finite volume method together with non‐staggered curvilinear grid is a very effective approach to capture interface shape with time. Because of the interface shape, for any time advancement, a new grid is performed separately on each stratified field, liquid, and gas regime. The results are compared with the analytical characteristics method and one‐dimensional modeling. This comparison shows that solving the momentum equation including viscosity term leads to physically more realistic results. In addition, the newly developed method is capable of predicting two‐phase stratified flow behavior more precisely than one‐dimensional modeling. It was perceived that the surface tension has an inevitable role in dissipation of interface instability and convergence of the two‐phase flow model. Copyright © 2009 John Wiley & Sons, Ltd.     

Application of the Density-Functional Method for Numerical Simulation of Flows of Multispecies Multiphase Mixtures

Numerical examples of application of the density functional used to describe isothermal flows of two-phase two-species mixtures are given. The following flows are calculated in a two-dimensional formulation: impact of a drop on a liquid layer, breakdown of a drop in the velocity field of the Couette flow, formation of the wetting angle of a drop on a solid surface, and development of the Rayleigh–Taylor and Kelvin–Helmholtz instabilities at the gas–liquid interface.     

管道凸起激波/湍流边界层干扰的数值模拟

采用基于部分平均的湍流方程组,模拟了管道凸起流动中两种不同强度的激波-湍流边界层干扰现象,对流场的时均参数与实验值进行了比较,计算得到的壁面压力分布、摩阻系数分布、边界层厚度和速度型与实验值比较吻合很好.结果表明基于部分平均的湍流方程组既能够准确模拟小分离的激波/湍流边界层干扰流动又能够准确模拟大分离的激波/湍流边界层干扰流动,较好地预测了典型的λ激波结构.