复式断面明渠三维紊流的数值模拟

本文采用非线性ｋ－ε紊流模型和Ｎａｏｔ－Ｒｏｄｉ代数应力模型（Ｎ－Ｒ模型）模拟复式断面明渠三维紊流。非线性ｋ－ε模型用张量形式推出，适用于边界形状复杂的流动，而Ｎ－Ｒ模型采用一种补充关系式反映计算点与界面距离对雷诺应力的影响，能较好地反映界面的作用。对一个复式断面明渠实例进行计算，给出了流速场（包括主流、二次流），壁面剪切力和雷诺应力分布，并与实验结果进行详细比较，还研究了浅滩粗糙壁面时的流动，除     

三维紊流模型的开发及其在环境工程中的应用

本文针对复杂的三维弯道水流，研究开发了三维代数插值坐标变换法；应用雷诺平均Ｎ－Ｓ方程和Ｋ－ε紊流模型，及曲率校正模式，对大朝山水电站城门洞式大型导流洞三维紊流进行了数值模拟；在１：１００的整体导流模型上做了试验，测取了洞内各部位的沿程压力分布；并将计算结果与实测值进行了对比。     

非恒定水深平均的K－ε紊流模型的有限元模式

本文在水深平均的二维流动的数学模型基础上，引入Ｋ－ε二方程模式，建立了水深平均的Ｋ－ε紊流模型，采用能适应不规则边界的有限元计算模式，对易引起不稳定的对流项引进迎流技巧，从而大大提高了计算稳定性。针对应用到河口海湾中的紊流模型具有大尺度计算网格的特点，本文分析了常用壁面律的局限性，比较了Ｋ方程中ＧＫ项与ＧＫＶ项的大小，并分析了紊流模型的优点。     

非恒定水深平均的K—ε紊流模型的有限元模式

本文在水深平均的二维流动的数学模型基础上，引入Ｋ－ε二方程模式，建立了水深平均的Ｋ－ε紊流模型，采用能适应不规则边界的有限元计算模式，对易引起不稳定的对流项引起迎流技巧，从而大大提高了计算稳定性，针对应用到河口海湾中的紊流模型具有大尺度计算网格的特点，本文分析了常用壁面规律的局限性，比较了Ｋ方程中Ｇｋ项与Ｇｋ项与Ｇｋｖ项的大小，并分析了紊流模型的优点。     

后壁受热二维矩形开口空腔中的紊流混合对流

利用Ｒｅ数下的Ｋ－ε紊流模型，对置于气流中的后壁受热二维矩形开口空腔中的紊流混合对流流动及换热作了数值研究。讨论了Ｇｒ数及Ｒｉ数对流场及温度场的影响，给出了当地及平均Ｎｕ数的变化规律。     

明渠高含沙水流的两个重要特性研究

本文从三维恒定雷诺方程式出发导出了计算二维均匀明渠高含沙水流紊流极限切应力τＢＴ的公式．公式中包含了紊动扩散系数εｍ，并通过分析天然河道实测资料和室内水槽试验资料研究了εｍ沿垂线分布的规律，结论是明渠高含沙水流的紊动扩散系数εｍ沿垂线分布规律和低含沙水流的类似，在河底处εｍ为０；在河底至相对水深０．２范围内εｍ随水深增加而变大，在相对水深０．２至水面范围内εｍ为常数．用所得τＢＴ计算公式对部分天然河道实测资料进行验算，大多数明渠高含沙水流属紊流流态，不存在紊流极限切应力τＢＴ     

压力洞闸槽进水的数值模拟与分析

本文应用Ｋ－ε紊流模型数值模拟了压力洞闸槽进水后洞内水流的流动情况。计算中，对Ｋ－ε方程及雷诺方程作者采用了皆沿坐标方向分步然后交叉求解的简便数值方法。计算实例所得结果与文献〔４〕试验资料一致。     

动床k—ε紊流模型研究

紊流ｋ－ε模型是近２０年发展起来的，并较适于模拟紊流运动的数学模型之一，它的特点是，用紊动动能ｋ和紊动能量耗散率ε来表征紊流的局部状态并封闭雷诺方程式。本文在紊流ｋ－ε模型和窦国仁悬沙冲淤模式的基础上，提出二维动床紊流ｋ－ε模型。并据此计算在明渠水流中设置方墩以后的河床冲淤变化。计算结果表明，该模型所预报的水流流态和河床冲淤部位与实际情况基本一致，且特别适用于有回流分离区的局部河段的河床变形的计算     

溢流坝反弧段紊动水流的数值模拟

本文采用非正交网格控制容积法及ｋ－ε二方程紊流模型，求解二维时间平均Ｎ－Ｓ方程，对反弧段紊流进行数值模拟。计算中分别采用了标准的考虑曲率修正的ｋ－ε紊流模型。后者计算结果与实测值符合良好。本文亦讨论了位置未知的自由水面的处理。     

同时存在温度和盐度梯度的分层流的数值模拟

本文对同时存在温度和盐度梯度的一类密度分层流进行了数值模拟,其中紊流平均量控制方程中的紊动项由一个简化的紊流应力/通量代数模型计算。计算结果正确地反映了分层及紊动特征,与实测结果吻合较好,而用k-ε紊流模型计算的结果与实测结果不符。     

Impact of depth ratio on flow structure and turbulence characteristics of compound open channel flows

Compound open channel flows appear in most natural rivers are of great importance in river management and flood control. In this study, large eddy simulations were carried out to simulate the compound open channel flows with four different depth ratios (h_r = 0.10, 0.25, 0.50, and 0.75). The main flow velocity, secondary flow, Reynolds stress, and bed shear stress were obtained from numerical simulations. The depth-averaged streamwise momentum equation was used to quantify the lateral momentum exchange between the main channel and floodplain. The instantaneous coherent structures were presented by the Q criterion method. The impact of h_r on flow structure and turbulence characteristics was analyzed. The results showed that with the increase of h_r, the high velocity area in the main channel shifted to the floodplain, and the dip phenomenon became more obvious; the Reynolds stress largely contributed to the lateral momentum exchange within the flows near the side walls of floodplain; and the vortex structures were found to significantly increase in the floodplain region.     

The mechanical energy equation for total flow in open channels

The mechanical energy equation is a fundamental equation of a 1-D mathematical model in Hydraulics and Engineering Fluid Mechanics. This equation for the total flow used to be deduced by extending the Bernoulli＇s equation for the ideal fluid in the streamline to a stream tube, and then revised by considering the viscous effect and integrated on the cross section. This derivation is not rigorous and the effect of turbulence is not considered. In this paper, the energy equation for the total flow is derived by using the Navier-Stokes equations in Fluid Mechanics, the results are as follows：（1） A new energy equation for steady channel flows of incompressible homogeneous liquid is obtained, which includes the variation of the turbulent kinetic energy along the channel, the formula for the mechanical energy loss of the total flow can be determined directly in the deduction process.（2） The theoretical solution of the velocity field for laminar flows in a rectangular open channel is obtained and the mechanical energy loss in the energy equation is calculated. The variations of the coefficient of the mechanical energy loss against the Reynolds number and the width-depth ratio are obtained.（3） The turbulent flow in a rectangular open channel is simulated using 3-D Reynolds averaged equations closed by the Reynolds stress model（RSM）, and the variations of the coefficient of the mechanical energy loss against the Reynolds number and the width-depth ratio are discussed.     

3-D hybrid LES-RANS model for simulation of open-channel T-diversion flows

The study of flow diversions in open channels plays an important practical role in the design and management of open-channel networks for irrigation or drainage.To accurately predict the mean flow and turbulence characteristics of open-channel dividing flows,a hybrid LES-RANS model,which combines the large eddy simulation (LES) model with the Reynolds-averaged Navier-Stokes (RANS) model,is proposed in the present study.The unsteady RANS model was used to simulate the upstream and downstream regions of a main channel,as well as the downstream region of a branch channel.The LES model was used to simulate the channel diversion region,where turbulent flow characteristics ate complicated.Isotropic velocity fluctuations were added at the inflow interface of the LES region to trigger the generation of resolved turbulence.A method based on the virtual body force is proposed to impose Reynolds-averaged velocity fields near the outlet of the LES region in order to take downstream flow effects computed by the RANS model into account and dissipate the excessive turbulent fluctuations.This hybrid approach saves computational effort and makes it easier to properly specify inlet and outlet boundary conditions.Comparison between computational results and experimental data indicates that this relatively new modeling approach can accurately predict open-channel T-diversion flows.     

明渠中掺气水流紊流流动规律

本文利用变密度变粘度流体在明渠中紊流流动时的运动微分方程式，研究了明渠中掺气水流紊流流动规律，得出，明渠中的掺气紊流不能在相同条件下增大明渠水流量，即不能实现有效的减阻。文中提出了密度紊动应力、粘度紊动应力、流量增加率等概念。     

变断面明渠柔性植物水流特性试验研究

在变断面明渠,利用ADV测量流速,研究断面突然扩大情况下模型植物和真实植物的水流特性。结果表明:在水流稳定区域,布设真实鸢尾草和塑料鸢尾草模型的流速分布、雷诺应力分布和紊动强度分布具有一定相似性;雷诺应力和紊动强度在相对水深为0.6～1.1区域达到峰值,且从峰值区域向两端递减,总体上植物下部区域的紊动强度比植物上部区域大;同种植物紊动强度沿x、z方向的分布形式存在较大差别,紊动强度存在明显各向异性。     

《南水北调与水利科技》优先数字出版声明

The turbulent flows through the channels with abrupt cross-sectional changes are common and importantphysical process in nature.For a better prediction of the mean flow and turbulent characteristics for this problem,atwo-dimensional depth-averaged numerical model is developed.The model is robust and accurate in reproducing therecirculation flow behind a groyne and turbulent flows in channels with abrupt cross-sectional changes,when com-pared to the available experimental data of mean velocities and turbulence kinetic energy.Our results reveal that theabrupt cross-sectional change of a channel can affect the flow pattern significantly and introduces the complex turbu-lence characteristics.In particular,when the channel has an abrupt expansion,the mean flow pattern is mainly in lon-gitudinal direction with rather small transverse component.Meanwhile,a recirculating region forms behind the expan-sion position and the turbulence has very strong intensity within this region.For the flow in the channel with an ab-rupt contraction,the longitudinal component of the flow is decreased by the obstruction on one side and accelerated onthe other side,whereas the transverse velocity is small.The turbulence is extraordinarily strong in the regions adja-cent to the contraction wall in the narrow channel.In both cases of abrupt cross-sectional changes,the TKE is genera-ted dominantly by the shear of the longitudinal velocities.     

湍流近壁区非线性模型的应力相位研究

近年来的研究结果显示,在非平衡湍流中,线性湍流模型中的雷诺应力与平均速度变形率之间存在着相位差,但是非线性湍流模型中是否也存在这个问题,至今还没有文献涉及。针对这一问题,该文对空间周期性吹吸边界条件的槽道湍流进行了直接数值模拟。研究发现,在湍流近壁区,剪切变形的相位在典型的非线性湍流模型的主要项中起着主导作用,这使得雷诺应力与相应的模拟项之间存在相位差。因此在建立有关非线性湍流模型时也应该注意这一问题。     

二维明渠非恒定水流BGK数值模型

本文根据BGK波尔兹曼方程及明渠水流中波尔兹曼变量与宏观变量之间的基本关系，导出了明渠水流运动方程，验证了BGK波尔兹曼方程与明渠水流运动方程的一致性，并从理论上证明，圣维南方程是BGK明渠水流模型在局部平衡状态下的一个特例。以BGK波尔兹曼方程为基本方程，利用有限体积离散方法，建立了满足熵原理的二维明渠非恒定水流的BGK数值模型。通过对典型的明渠水流现象的模拟，并与其它计算方法获得的解以及实验结果相比较，表明BGK模型勿须人为的熵修正，能准确地模拟存在不连续运动的明渠水流运动，是一种较好的明渠非恒定水流模型。     

明渠均匀流流速横向分布的涡黏性模型

为了研究明渠水流的运动特性,开展了明渠水流流速横向分布数学模型的研究。本文根据量纲分析方法和实验资料,得到水流横向剪切作用下横向涡黏性系数的关系式;基于均匀流的水流运动方程,按照有限差分方法,建立流速横向分布计算模型。该模型具有计算简单、快捷和精度较高的优点,且数值计算不受横向涡黏性系数的结构形式和断面形态的影响。采用明渠水流实验资料验证数学模型,数学模型计算的流速横向分布与实验资料较一致,具有较高的理论意义和应用价值。     

The influence of nonlinear shear stress on partially averaged Navier-Stokes(PANS) method

In most of partially averaged Navier-Stokes(PANS)methods,the Reynolds stress is solved by a linear hypothesis isotropic model.They could not capture all kinds of vortexes in tubomachineries.In this paper,a PANS model is modified from the RNG k-?turbulence model and is used to investigate the influence of the nonlinear shear stress on the simulation of the high pressure gradient flows and the large curvature flows.Comparisons are made between the result obtained by using the PANS model modified from the RNG k-?model and that obtained by using the nonlinear PANS methods.The flow past a curved rectangular duct is calculated by using the PANS methods.The obtained nonlinear shear stress agrees well with the experimental results,especially in the high pressure gradient region.The calculation results show that the nonlinear PANS methods are more reliable than the linear PANS methods for the high pressure gradient flows,the large curvature flows,and they can be used to capture complex vortexes in a turbomachinary.