基于分离涡模拟的核主泵全工况水力性能计算精度研究

为了研究分离涡模拟模型对核主泵水力性能预测精度的影响,在六面体结构化网格的基础上,采用基于SSTκ-ω的分离涡模拟(DES)、延迟分离涡模拟(DDES)和改进的延迟分离涡模拟(IDDES),分别进行全流量工况条件下的非定常数值计算,并与RNGκ-ε模型的计算结果作对比,从相对计算误差的大小和离散度2个方面对4种湍流模型的计算精度进行综合评判。研究结果表明:各分离涡模拟模型在全流量工况点的综合计算精度远高于RNGκ-ε模型;DDES和IDDES模型在全流量工况条件下的计算精度基本一致,并且都高于DES模型;DDES模型在设计工况点附近的计算精度明显优于IDDES。综合比较来看,DDES模型更适用于核主泵的性能预测。     

湍流模型对过冷沸腾计算影响分析

采用ANSYS FLUENT14.5分析湍流模型对过冷沸腾的影响,建立多套网格,每套网格采用不同的湍流模型、壁面函数及两相湍流处理方法,将计算结果与基准实验数据进行对比,分析网格、湍流模型、壁面函数及两相湍流处理方法对计算精度的影响。通过分析发现:k-ε模型的计算精度高于k-ω模型的;Dispersed方法和Per Phase方法的计算精度相对于Mixture的无明显提升;增强壁面函数对Y+≈1的网格无法获得满意的计算结果。     

核反应堆冷却剂循环泵全流道三维数值模拟及性能预估

为实现核反应堆冷却剂循环泵（核主泵）的设计自主化及制造国产化,通过CFD数值模拟软件FLUENT,应用RNGk-ε湍流模型及SIMPLE算法对某核主泵进行全流道三维数值模拟,获得了在不同工况下的叶轮内部流动情况,分析了压力和速度分布规律,并进行了性能预估。结果表明,稳态工况下叶片的工作面与背面的压力分布与速度分布合理;泵段压力总体上由进口端至出水端呈递增趋势且在叶轮段出现最大值;在设计工况点得到了较为理想的泵效率与扬程值;随着流量的增加,核主泵的轴功率也逐步增加。模拟结果有助于认识核主泵在运转状态下的内部流场变化情况,为核主泵的国产化前期探索和理论研究提供支持。     

硝酸盐自然循环回路空冷塔性能分析

硝酸盐自然循环回路(Nitrate Natural Circulation Loop,NNCL)是先进熔盐堆非能动衰变热排出系统的实验回路,目的是获得自然循环下回路的传热、阻力等特性,验证计算分析方法的正确性等。本文采用RNG(Renormalization Group)k-ε湍流模型、增强壁面函数和SIMPLE(Semi-Implicit Method for Pressure Linked Equations)算法,对硝酸盐自然循环回路空冷塔部分的对流换热进行了数值模拟研究。计算结果表明:空冷换热器旁路漏流对换热有较大影响,可以通过旁路挡板增强换热能力,三层旁路挡板的设计能将换热能力提升近一倍。     

M310压水堆核电厂离心式上充泵首级叶轮汽蚀特性

采用Pro/E和ICEM软件进行水体部件的三维造型和网格划分,确定以Reynolds时均的N-S方程、RNG k-ε两方程湍流模型、SIMPLEC算法和汽蚀模型为基础的数值计算方法,完成对上充泵首级叶轮汽蚀特性的非稳态数值模拟及试验对比研究。计算结果表明:在汽蚀初生时,气体体积分数对叶轮流道内部的压力影响较小;在临界汽蚀余量,靠近叶片进口处的汽蚀变化对压力的影响较大;临界汽蚀余量的模拟和试验结果分别为7.35 m和7.58 m,误差约为2%,均满足核电规范要求。     

单相4×4棒束流动试验的CFD方法验证

为研究计算流体力学（CFD）方法预测棒束通道内流场分布的准确性,基于网格敏感性分析所确定的网格方案,采用标准k-ε模型（SKE）、可实现k-ε模型（RKE）、标准k-ω模型（SKW）和剪切应力传输模型（SST模型）对单相棒束流动进行模拟,并将横向速度与轴向速度与试验结果进行量化比较。结果表明:4种湍流模型均能较好地预测棒束通道内的流场分布,其中SKE与RKE的在横向速度预测上相对偏差较小,为19.6%;对于近格架区域的横向流场分析,SKE模拟较优,反之RKE模拟较优;对于轴向速度的预测,SKE的相对偏差最小为4.9%;4种湍流模型均低估均方根（RMS）速度,但能够预测棒束通道内RMS速度的分布规律,近格架区域采用RKE,反之SST较优。本文的计算结果可为单相棒束流动CFD分析的最佳实践导则建立提供参考。      

模型泵内部流场的数值模拟

采用雷诺时均N-S方程和标准k-ε湍流模型,应用三维非结构四面体网格建模,选用旋转流体机械模型中的多重参考坐标系模型(MRF),对设计工况下反应堆主冷却剂泵模型泵的三维不可压缩湍流流场进行了数值模拟,模拟结果较好地揭示了内部流场的特点.本文分析了流场内总的压力分布和速度分布,描述了叶轮、导叶和球壳各个部分的内部流场特征,并探讨了造成这些特征的原因.研究结果可用于反应堆主冷却剂泵的性能预测,并为其水力优化设计提供有益参考.     

湍流模型对安全壳内氢气浓度场模拟的影响

利用计算流体力学程序FLUENT和GASFLOW研究了不同湍流模型下，氢气在安全壳内的传输与混合过程。计算结果表明：RNG k-ε模型能够得到较合理的结果，它能够较好的模拟氢气的质量扩散，动量扩散和湍流特征；FLUENT标准k-ε模型、标准k-ε模型和GASFLOW中k-ε模型能够在氢气浓度场分布上得到与RNGk-ε模型基本一致的结果，但由湍流导致的各种流动参数的波动不能在前三个模型中得到满意的模拟；GASFLOW中代数模型没能较好的模拟氢气的质量扩散和动量扩散，氢气的浓度场分布与其他模型的计算结果存在较大的差别。因此，选择合适的湍流模型，对于研究严重事故下安全壳内的氢气分布有重要的意义。     

壁面辐射对具有内置翅片的封闭腔内湍流自然对流传热特性影响

为研究有内置翅片的封闭腔内壁面发射率（ε）对腔内湍流自然对流传热特性的影响,采用RNG k-ε湍流模型对流体为空气、高宽比为1的封闭腔内的温度场、流场、壁面传热能力进行数值分析。结果表明:内置翅片与壁面辐射的综合效应使得竖向热边界层和速度边界层厚度均增大,腔体顶部及底部区域水平速度产生了一定波动。考虑壁面辐射时,双翅片结构对热壁面局部传热能力的影响趋势与单翅片结构类似;ε为0.3、0.6、0.9时,单翅片对热壁面平均努塞尔数（Nu）分别提高39.95%、88.55%和144.97%,双翅片对热壁面平均Nu分别提高41.09%、87.32%和141.23%;ε过大对双翅片结构的封闭腔内对流散热反而不利。      

气-液条件下导叶出口位置对反应堆冷却剂主泵性能的影响

为研究在气-液两相流条件下,导叶出口边安放位置对反应堆冷却剂主泵(主泵)内部流场特性的影响,采用三维建模软件Pro/E建模,网格划分软件IECM划分非结构网格,计算流体动力学(CFD)软件CFX进行数值模拟。模拟过程中采用雷诺时均N-S方程和k-ε湍流模型,使用多相流模型中的混合物模型对主泵在气-液两相条件下的内部流场进行数值模拟。对不同导叶出口边安放位置时泵壳和导叶内的含气率分布、液相和气相相对速度分布进行研究。结果表明,在气-液两相流条件下,不同导叶出口边安放位置对导叶和泵壳内的含气率、相对速度分布有一定的影响;不同导叶出口边安放位置时,泵壳内的气体聚集程度不一样,当导叶出口边位于泵壳中心垂直平面上时,泵内部流动效果最佳。     

An assessment of k-ε turbulence models for gas distribution analysis

This paper presents the gas distribution analysis by injecting air fountain into the containment and simulations with the HYDRAGON code. Turbulence models of standard k-ε(SKE), re-normalization group k-ε(RNG) and a realizable k-ε(RLZ) are used to assess the effects on the gas distribution analysis during a severe accident in a nuclear power plant. By comparing with experimental data,the simulation results of the RNG and SKE turbulence models agree well with the experimental data on the prediction of dimensionless density distributions. The results illustrate that the turbulence model choice had a small effect on the simulation results, particularly the region near to the air fountain source.     

二维孔隙结构内单相流动阻力特性数值模拟

利用计算流体力学(CFD)商业软件CFX 10.0,采用标准k-ε、RNG k-ε以及SST模型3种不同的湍流模型,对矩形管内球形颗粒作2维有序排列所形成的孔隙流道的等温单相流动进行数值模拟,并与Ergun关系式预计值进行对比;探讨球形颗粒的排列方式、直径等对单相流动阻力的影响;研究矩形管内单位长度压降及阻力系数随孔隙雷诺数Re的变化规律(1.5≤Re≤1497)。     

Benchmark Simulation of Turbulent Flow through a Staggered Tube Bundle to Support CFD as a Reactor Design Tool. Part I: SRANS CFD Simulation

Time-invariant and time-variant numerical simulations of flow through a staggered tube bundle array, idealizing the lower plenum (LP) subsystem configuration of a very high temperature reactor (VHTR), were performed. In Part I, the CFD prediction of fully periodic isothermal tube-bundle flow using steady Reynolds-averaged Navier-Stokes (SRANS) equations with common turbulence models was investigated at a Reynolds number (Re) of 1.8 × 10⁴, based on the tube diameter and inlet velocity. Three first-order turbulence models, standard k-ε turbulence, renormalized group (RNG) k-ε, and shear stress transport (SST) k-ω models, and a second-order turbulence model, Reynolds stress model (RSM), were considered. A comparison of CFD simulations and experiment results was made at five locations along (x, y) coordinates. The SRANS simulation showed that no universal model predicted the turbulent Reynolds stresses, and generally, the results were marginal to poor. This is because these models cannot accurately model the periodic, spatiotemporal nature of the complex wake flow structure.     

Validation of a Computational Simulation Method for Evaluating Thermal Stratification in the Reactor Vessel Upper Plenum of Fast Reactors

Validation of a numerical simulation method is carried out for thermal stratification phenomena in the reactor vessel upper plenum of advanced sodium-cooled fast reactors. The study mainly focuses on the fundamental applicability of commercial computational fluid dynamics (CFD) codes as well as an inhouse code to the evaluation of thermal stratification behavior including the simulation methods such as spatial mesh distribution and RANS-type turbulence models in the analyses. Two kinds of thermal stratification tests are used in the validation, which is done for relatively simple- and conventional-type upper plenum geometries with water and sodium as working fluids. Quantitative comparison between the simulation and test results clarifies that when used with a high-order discretization scheme of the convection term, the investigated CFD codes are applicable to evaluations of the basic behaviors of thermal stratification and especially the vertical temperature gradient of the stratification interface, which is important from the viewpoint of structural integrity. No remarkable difference is seen in the simulation results obtained using different RANS turbulence models, namely, the standard kε model, the RNG k-ε model, and the Reynolds stress model. It is further confirmed in a numerical experiment that the distribution of two or more meshes within the stratification interface will lead to accurate simulation of the interface temperature gradient with less than 10% error.     

Numerical Simulation of Heat Transfer of Supercritical Fluids in Circular Tubes Using Different Turbulence Models

In this study, the heat transfer of supercritical fluids in vertical and horizontal circular tubes has been investigated numerically to understand the thermal-hydraulic behavior of supercritical fluids. The simulations are carried out using different turbulence models and the numerical results are compared with the experimental data to evaluate the accuracy and applicability of those turbulence models. Six turbulence models are used in this study, the LB low-Re k-? model, the LS low-Re k-? model, the RNG k-? model, the realizable k-? model, the standard k-? model, and the Reynolds stress model. The comparison shows that the Reynolds stress model gives better agreement with the experimental data than other turbulence models studied in this work.     

液态LBE介质轴流泵压力脉动特性数值研究

基于雷诺时均N-S方程和重整化群（RNG）k-ε湍流模型,研究分析了轴流泵在常温清水和液态铅-铋合金（LBE）介质下的水力性能和压力脉动特性及其分布规律。结果表明:按照常温清水介质水力设计方法及相关经验系数完成的轴流泵的水力设计方案,在LBE介质条件下,泵扬程和效率相对有所提高,随着流量增大,扬程明显增加;泵内边界层脱流现象明显减弱;泵叶轮进口监测点的压力系数脉动主频为81 Hz,与叶片转频相等,在2倍以及3倍叶频处出现次频谐波;介质粘性的差异不影响叶轮进口处的压力脉动系数幅值,介质密度即惯性力与泵叶轮进口压力脉动幅值呈线性正相关。      

转子悬臂比对核主泵水力振动的影响

为研究转子悬臂比对核主泵水力振动的影响规律,针对CAP1400核主泵,在其他几何参数均给定的条件下,通过改变泵轴的悬臂比,设计了25个模型方案。应用多重参考系下的雷诺时均N-S方程和RNG k-ε湍流模型对核主泵流体域进行了计算,采用单向流固耦合方法,分析了核主泵叶轮叶片的应力、应变在不同悬臂比、不同工况下的变化规律,并在有预应力和无预应力情况下,对不同悬臂比的核主泵进行了转子动力学特性研究。结果表明：当泵轴伸出端长度一定时,核主泵叶轮叶片的应力、应变及转子系统的前6阶固有频率与悬臂比的相关性不强,但对工况变化的敏感度较高;相同工况下,核主泵叶轮叶片的最大变形量随悬臂长度而增大,但不随悬臂比而变化,最大应力不随悬臂长度及悬臂比而变化;流固耦合作用能降低转子系统的固有频率,且降低幅度随阶数的增加而减小。