计算风工程中k-ε模型的一类边界条件

给定适当的湍流来流边界条件是计算风工程中一个重要的问题。然而通常情况下 ,由于问题的复杂性 ,很难给定一个既满足边界层自保持要求又与试验相符的边界条件。本文首先从模型方程本身出发 ,推导出一类近似满足κ ε模型自保持边界条件要求的湍动能表达式。此表达式与有关文献建议的湍流边界条件比较 ,可以考虑湍动能随高度的变化 ,因而更符合实测规律 ;然后基于风洞试验数据 ,定义了一组k ε模型中的模型常数 ;最后通过模拟风洞试验的算例 ,验证并分析了此类湍动能边界条件配合试验常数 ,在标准k

基于标准k-ε模型的平衡大气边界层模拟

基于标准k-ε模型和FLUENT软件,采用适当的平均风和湍流特征量入口条件,同时在壁面处采用修正壁面函数边界条件,进行空流场的平衡大气边界层模拟。将流场中不同位置处的平均风廓线、湍动能及其粘性耗散等流动特征量的廓线进行对比。结果表明,采用标准k-ε模型结合修正壁面函数对气流流经粗糙度相同的壁面时,不同位置处流动特征量的廓线吻合程度均较高。研究提出对建筑绕流等问题模拟之前需进行空流场的平衡性进行分析,另对文中尚未解决的问题进行讨论并提出解决思路。

基于标准K-ε模型与CFD的浮子流量传感器的研究

依据湍流模式理论中的标准 K- ε模型及 CFD(计算流体力学 )实现了对浮子流量传感器三维湍流流场的数值研究 ,利用物理概念清晰的“有限体积法”作为数值解法 ,并采用以压力为基本求解变量的 SIMPL E算法求解离散控制方程 ;提出“浮子受力平衡度误差分析法”控制计算精度 ,通过对传感器速度场、压力场的三维研究 ,获得传感器流场的关键信息 ,即浮子受力大小以及传感器流量值。数值计算结果 ,即针对 30 0 K水 ,粘度为 1.0 0 3× 10 - 3Pa· s流场的计算结论得到了物理实验验证。

不可压湍流流动K-ε两方程模型参数辨识

本文提出了不可压湍流流动情况下标准 K -ε两方程模型的参数辨识方法 ,并对轴对称管道流动、二维后向台阶流动、轴对称突扩管道流动下的模型参数进行了参数辨识与分析 ,得到了一些初步结论 :( 1)参数辨识方法是确定湍流模型经验参数值的一种有效方法 ;( 2 )参数辨识结果受数值计算精度和流动特性影响很大 ;( 3)由于标准 K -ε两方程模型本身还有缺陷 。

基于k-ε模型模拟平衡态大气边界层的比较研究

平衡态大气边界层的准确模拟是计算风工程领域的基础性难题,也是研究热点问题之一。该文首先对近年来国内外针对这一问题的理论研究成果按入流边界条件、湍流模型参数、附加源项模型以及壁面函数模型等四个方面进行了全面梳理和系统总结,并建议了一组新的标准k-ε模型湍流模型参数和通用壁面函数模型表达式。接着,采用计算流体动力学方法,建立简单边界层流动数值风洞模型,按照以上四种类别采用递进的方法对这些理论成果进行了详细的数值模拟验证和比较分析。结果表明:基于湍动能k方程解析解的入流边界条件并不必然会生成平衡态边界层,它和湍动能剖面的数学模型表达形式关系很大;除入流湍流边界条件外,湍流模型参数取值及壁面函数对平衡态大气边界层的模拟亦有较大影响,而增加源项并不能有效改善速度和湍动能剖面在整个流域范围的自保持性。该文对这一类问题的研究具有一定参考价值。

基于标准k-ε模型的汽车节气门三维流场数值仿真

针对一种具体型号的节气门体建立了几何模型。用基于Fluent软件的标准k-ε模型对节气门三维流场进行数值仿真。仿真结果与实验结果吻合非常好,表明了标准k-ε模型在汽车节气门流场仿真中的适用性。仿真结果为汽车节气门体流场分析和节气门结构的改进提供参考。

基于标准k-ε模型的平衡大气边界层研究

平衡态大气边界层的精确模拟是计算风工程研究中的一项重要且容易被忽视的工作。文章基于标准k-ε模型的控制方程,对大气边界层的平衡条件作出适当假设,总结了与剪应力相关的入流边界条件的通用形式。为实现大气边界层的自保持,在湍动能和耗散率输运方程中添加源项使入流边界条件与湍流模型相协调,并对顶部和底部边界条件施加剪应力修正;然后,分别以二维缩尺和足尺模型为例进行了平衡大气边界层的模拟。研究发现,在湍动能和耗散率输运方程中添加源项对改善大气边界层的自保持产生了不可忽略的影响,在顶部和底部施加剪应力能较好地改善顶部和底部大气边界层的自保持效果,通过同时添加源项和施加剪应力能很好地实现大气边界层的自保持。

Strong ground motion simulation for the 2013 Lushan M_W6.6 earthquake, Sichuan, China, based on the inverted and synthetic slip models

It is well known that quantitative estimation of slip distributions on fault plane is one of the most important issues for earthquake source inversion related to the fault rupture process. The characteristics of slip distribution on the main fault play a fundamental role to control strong ground motion pattern. A large amount of works have also suggested that variable slip models inverted from longer period ground motion recordings are relevant for the prediction of higher frequency ground motions. Zhang et al. （Chin J Geophys 56：1412-1417, 2013） and Wang et al. （Chin J Geophys 56：1408-1411,2013） published their source inversions for the fault rupturing process soon after the April 20, 2013 Lushan earthquake in Sichuan, China. In this study, first, we synthesize two forward source slip models： the value of maximum slip, fault dimension, size, and dimension of major asperities, and comer wave number obtained from Wang＇s model is adopted to constrain the gen- eration of k-2 model and crack model. Next, both inverted and synthetic slip models are employed to simulate the ground motions for the Lushan earthquake based on the stochastic finite-fault method. In addition, for a comparison purpose, a stochastic slip model and another k-2 model （k 2 model II） with 2 times value of comer wave number of the original k-2 model （k 2 model I） are also employed for simulation for Lushan event. The simulated results characterized by Modified Mer- calli Intensity （MMI） show that the source slip models based on the inverted and synthetic slip distributions could capture many basic features associated with the ground motion patterns. Moreover, the simulated MMI distributions reflect the rupture directivity effect and the influence of the shallow velocity structure well. On the other hand, the simulated MMI bystochastic slip model and k 2 model II is apparently higher than observed intensity. By contrast, our simulation results show that the higher frequency ground motion is sensitive to the degree of slip roughness; therefore, we suggest that, for realistic ground- motion simulations due to future earthquake, it is imperative to properly estimate the slip roughness distribution.

K-means聚类算法在高压开关设备机械状态评估中的应用

在对智能高压开关设备进行在线监测评估时,核心的问题是标准数据模型的建立,标准数据模型的好坏直接决定评估结果的可信度,提出一种基于K-means聚类算法在建立高压开关设备机械状态评估标准数据模型上的应用方法,并以自主研制开发的126 k V智能GIS为研究对象,在大量现场实验数据的基础上对智能GIS机械状态评估进行分析和探索。实验结果表明:该方法执行速度快,可靠性高,具有非常良好的实用性,非常适宜在智能高压开关设备机械状态评估中应用。

新型导流式固-液旋流分离器流场的数值模拟

针对新型固-液旋流分离器实际操作中的相关问题,阐述固-液旋流分离器分离机理,使用计算流体力学软件Fluent及前处理软件Gambit对新型固-液旋流分离器进行三维建模、分块网格划分和迭代计算。设计能够有效缓解循环流破坏性影响的导流板这一特殊结构,结合欧拉多相流分析法和标准k-ε湍流模型对其进行数值模拟。根据旋流分离理论,计算得到流场的压力分布、速度分布、粒子轨迹分布等规律。结果表明,新型导流式固-液旋流分离器对直径在5μm以上的颗粒能够较好地分离;对旋流分离器上柱段压力损失严重的情况应从旋流分离器设计方面予以改进。

基于高斯分量标准化的K近邻故障检测策略

针对复杂多工况工业过程故障检测问题,提出一种基于高斯分量标准化的K近邻(Gaussian Component Standardization K-Nearest Neighbor,GCS-KNN)故障检测策略。样本数据应用高斯混合模型(Gaussian Mixture Model,GMM)进行训练,将数据分解为多个高斯分量;通过每个高斯分量的均值和协方差对该分量内的数据进行标准化处理;应用K近邻(K-Nearest Neighbor,KNN)算法对标准化后的样本进行检测。GCS-KNN通过高斯分量标准化消除数据的多模态特性,提高传统基于KNN检测方法的检测率。利用数值例子和半导体工业过程仿真实验验证了该方法的有效性,并与传统的主元分析(Principal Component Analysis,PCA)、KNN、动态主元分析(Dynamic PCA,DPCA)和加权KNN(Weighted KNN,WKNN)等方法进行对比,结果证实此方法具有显著的优势。

CFD Prediction of the Airflow at a Large-Scale Wind Farm above a Steep, Three-Dimensional Escarpment

The Duogu Wind Farm, China Huadian Group Corporation’s first wind project in Yunnan, China, has been approved by the Provincial Development and Reform Commission. The acquired site is in Mengzi, in the south-east of Yunnan Province. The developer has deployed thirty-three 1.5 MW turbines in this wind farm (49.5 MW), and the total cost of construction has been estimated to be CNY449.7 million ($69.61 million). The present study compared the prediction accuracy of two CFD software packages for simulating flow over an escarpment with a steep slope. The two software packages were: 1) Open FOAM (Turbulence model: SST k-ω RANS), which is a free, open source CFD software package developed by Open CFD Ltd at the ESI Group and distributed by the Open FOAM Foundation and 2) RIAM-COMPACT (Turbulence model: Standard Smagorinsky LES), which has been developed by the lead author of the present paper. Generally good agreement was obtained between the results from the simulations with Open FOAM and RIAM-COMPACT.

Experimental and Numerical Study of Dilute Gas-Solid Flow inside a 90°Horizontal Square Pipe Bend

A pneumatic test rig is built to test a curved 90° square bend in an open-circuit horizontal-to-horizontal suction wind tunnel system. Sand particles are used to represent the solid phase with a wide range of particle diameters. Velocity profiles are constructed by measuring the gas velocity using a 3-hole probe. Flow patterns inside the bend duct are introduced using sparks caused by burning sticks of incense with the air flow inside the piping system for flow visualization purpose. Numerical calculations are performed by Lagrangian-particle tracking model for predicting particle trajectories of dispersed phase, and standard k-ε model for predicting the turbulent gas-solid flows in bends. Comparisons made between the theoretical results and experimental data for the velocity vectors and particle trajectories show good agreement.

Determination of Flow Structure in a Gold Leaching Tank by CFD Simulation

Experimental residence time distribution (RTD) measurement and computational fluid dynamics (CFD) simulation are the best methods to study the hydrodynamics of process flow systems. However, CFD approach leads to better understanding of the flow structure and extent of mixing in stirred tanks. In the present study, CFD models were used to simulate the flow in an industrial gold leaching tank. The objective of the investigation was to characterize the flowfield generated within the tank after process intensification. The flow was simulated using an Eulerian-Eulerian multi-fluid model where the RANS standard kmixture model and a multiple reference frame approach were used to model turbulence and impeller rotation respectively. The simulated flowfield was found to be in agreement with the flow pattern of pitched blade axial-flow impellers that was used for mixing. The leaching tank exhibited good “off-bottom suspension” which reveals minimum deposition of gold ore particles on the bottom of the leaching tanks. Simulation results were consistent with experimental results obtained from a radioactive tracer investigation. CFD approach gave a better description of the flow structure and extent of mixing in a leaching tank. Hence it could be a preferred approach for flow system analysis where the cost of experimentation is high.

NUMERICAL SIMULATION OF 3-D TURBULENT FLOWS OVER DREDGED TRENCHES

A 3- D free surface flow in open channels based on the Reynolds equations with the k-ε turbulence closure model is presented in this paper. Insted of the 'rigid lid' approximation, the solution of the free surface equation is implemented in the velocity-pressure iterative procedure on the basis of the conventional SIMPLE method. This model was used to compute the flow in rectangular channels with trenches dredged across the bottom. The velocity, eddy viscosity coefficient, turbulent shear stress, turbulent kinetic energy and elevation of the free surface can be obtained. The computed results are in good agreement with previous experimental data.

A New Efficient Finite Volume Modeling of Small Amplitude Free Surface Flows with Unstructured Grid

A staggered finite-volume technique for non-hydrostatic, small amplitude free surface flow governed by the incompressible Navier-Stokes equations is presented there is a proper balance between accuracy and computing time. The advection and horizontal diffusion terms in the momentum equation are discretized by an integral interpolation method on the orthogonal unstructured staggered mesh and, while it has the attractive property of being conservative. The pressure-correction algorithm is employed for the non-hydrostatic pressure in order to achieve second-order temporal accuracy. A conservative scalar transport algorithm is also applied to discretize k - c equations in this model. The eddy viscosity is calculated from the k-c turbulent model. The resulting model is mass and momentum conservative. The model is verified by two examples to simulate unsteady small amplitude free surface flows where non-hydrostatic pressures have a considerable effect on the velocity field, and then applied to simulate the tidal flow in the Bohai Sea.

Part I: Explaining the “Muon g - 2” Results with Probabilistic Spacetime

A recent experimental finding replicated an earlier research result, both of which demonstrated conflict with a specific Standard Model prediction. The “Muon g - 2” studies have indicated that the degree of muon precession predicted by the Model is not the same as observed. The researchers offer many posteriori atheoretical hypotheses as possible explanations of their findings, but no fundamental theoretical understanding of the near discovery is among them. This article describes both an explication for the unexpected result and describes its underlying mechanism based on an existing cosmological theory, the Probabilistic Spacetime Theory. The paper also discusses the potential value of this theory.

基于湍流模型的飞行器温度场数值仿真研究

飞行器红外成像仿真需要不同飞行条件下的温度场分布。本文利用标准(Standard)k-ε模型、剪切应力传输(SST)k-ε模型和Spalart-Allmaras(S-A)模型分别进行数值模拟仿真计算,研究不同飞行速度和飞行高度下的飞行器温度场分布,并对不同模型的结果进行对比分析。首先,利用MultiGen Creator软件对飞行器进行三维建模;其次采用Hypemesh软件和Fluent meshing软件中进行面网格划分和体网格划分,最后采用Fluent 2022R1软件仿真飞行器静态温度场分布,通过改变湍流模型与边界条件设置,对不同飞行速度和不同高度下飞行器温度场进行数值模拟仿真,并与理论结果进行了对比分析。实验结果显示,3种湍流模型均能较好的模拟飞行器蒙皮与尾喷管内壁壁面温度值。飞行器蒙皮温度随着飞行马赫数的增加不断升高;随着飞行高度的升高而不断地降低,与理论结果变化规律一致。在尾喷管内壁面温度仿真中,3种湍流模型仿真的内壁面温度最高相差21 K,相对误差在1.8%左右,在红外仿真中近似忽略不计,故3种湍流模型均适合尾喷管内壁面温度场仿真。在蒙皮温度场仿真中,3种湍流模型仿真计算的蒙皮平均温度值与理论温度值的相对误差均在5%以内,均可满足红外成像仿真的温度差值要求,其中k-ε模型在蒙皮温度场模拟中与理论温度值最为接近,因此k-ε模型精度更高,更适合于飞行器的流场仿真,能更好地仿真出空气动力加热对飞行器温度场的影响。

高水头大流量拱坝水垫塘水动力特性数值模拟

高拱坝泄洪过程具有高水头、大流量以及高流速等特点,对水垫塘结构安全提出了更高要求。为分析高拱坝泄洪对水垫塘地板的影响,采用标准k-ε紊流模型并借助几何重构格式的VOF法追踪水垫塘内自由水面,模拟结果与实测结果相吻合。结合水垫塘底板压力分布与湍流粘度模拟结果,分析了高拱坝泄洪消能过程中水垫塘底板的水力特性以及其对磨蚀损伤的潜在影响。

风工程数值模拟中平衡大气边界层的研究与应用

基于RANS方法构造满足水平均匀性的自保持平衡大气边界层是计算风工程中一个非常重要但尚未得到很好的解释和解决、同时也经常被忽略的前提问题。本文从描述湍流流动的模型方程角度对这个问题进行了研究。首先基于湍流平衡假设,从两方程标准k-ε模型导出一类近似满足大气边界层自保持要求的湍流来流边界条件;接着将本文建议的此类边界条件运用到模拟钝体建筑结构分离流动具有较好适用性的SST k-ω湍流模型中,通过数值风洞模拟对比算例,验证了作者提出的边界条件在构造自保持平衡边界层中的适用性。通过本文的理论和数值研究,一方面对研究平衡大气边界层的模拟问题提供了一种新的方法,另一方面也为风工程数值模拟提供了一类新的适用的来流湍流边界条件,将对增进计算风工程中模拟平衡边界层的理解有所帮助,因此具有理论和实用价值。