数值反应堆堆芯通道级三维热工水力程序CorTAF开发及初步验证

堆芯是核动力系统的核心部件,其完整性是反应堆安全运行的重要前提。传统核反应堆堆芯热工水力分析方法无法满足未来先进核动力系统的高精度模拟需求。本文依托开源CFD平台OpenFOAM,针对压水堆堆芯棒束结构特点建立了冷却剂流动换热模型、燃料棒导热模型和耦合换热模型,开发了一套基于有限体积法的压水堆全堆芯通道级热工水力特性分析程序CorTAF。选取GE3×3、Weiss和PNL2×6燃料组件流动换热实验开展模型验证,计算结果与实验数据基本符合,表明该程序适用于棒束燃料组件内冷却剂流动换热特性预测。本工作对压水堆堆芯安全分析工具开发具有参考和借鉴意义。     

神威太湖之光上OpenFOAM的移植与优化

神威太湖之光是最新一期Top500榜单上排名第一的超级计算机,峰值性能为125.4 PFlops,其计算能力主要归功于国产SW26010众核处理器。OpenFOAM(Open Source Field Operation and Manipulation)是计算流体力学领域使用最广泛的开源软件包,但是由于其基于C++实现,与神威太湖之光上的异构众核处理器SW26010的编译器不兼容,因此无法直接在该架构上有效运行。基于SW26010的主核/从核的体系架构移植了OpenFOAM的核心计算代码,并采用混合语言编程实现的方式来解决编译不兼容的问题。此外,通过寄存器通信、向量化和双缓冲等优化手段,单核组的性能较优化后的主核代码提高了8.03倍,较Intel(R) Xeon(R) CPU E5-2695 v3的串行执行性能提高了1.18倍。同时,将单核组的实现扩展到了神威太湖之光的大规模集群上,并进行了强可扩展性测试,256个核组上实现了184.9倍的加速。采用的移植方式和优化手段也可以为其他复杂C++程序在神威太湖之光上的应用提供借鉴。     

Euler–euler anisotropic gaussian mesoscale simulation of homogeneous cluster‐induced gas–particle turbulence

An Euler–Euler anisotropic Gaussian approach (EE‐AG) for simulating gas–particle flows, in which particle velocities are assumed to follow a multivariate anisotropic Gaussian distribution, is used to perform mesoscale simulations of homogeneous cluster‐induced turbulence (CIT). A three‐dimensional Gauss–Hermite quadrature formulation is used to calculate the kinetic flux for 10 velocity moments in a finite‐volume framework. The particle‐phase volume‐fraction and momentum equations are coupled with the Eulerian solver for the gas phase. This approach is implemented in an open‐source CFD package, OpenFOAM, and detailed simulation results are compared with previous Euler–Lagrange simulations in a domain size study of CIT. The results demonstrate that the proposed EE‐AG methodology is able to produce comparable results to EL simulations, and this moment‐based methodology can be used to perform accurate mesoscale simulations of dilute gas–particle flows. © 2017 American Institute of Chemical Engineers AIChE J, 63: 2630–2643, 2017     

Numerical simulation of single bubble condensation in subcooled flow using OpenFOAM

The single condensing bubble behavior in subcooled flow has been numerical investigated using the open source code OpenFOAM. A coupled Level Set (LS) and Volume of Fluid (VOF) method (CLSVOF) model with a phase change model for condensation was developed and implemented in the code. The simulated results were firstly compared with the experimental results, they were in great agreements, and thus the simulation model was validated. The validated numerical model was then used to analyze the condensing bubble deformation, bubble lifetime, bubble size history, condensate Nusselt number and other interesting parameters with different variables in subcooled flow. The numerical results indicated that the initial bubble size, subcooling of liquid and system pressure play an important role to influence the condensing bubble behaviors significantly and bubble will be pierced when the subcooling and initial diameter reach a certain value at the later condensing stage. The bubble diameter history and condensate Nusselt number were found in good agreement with the empirical correlation. The drag force coefficient was predicted well by introducing a reduced drag coefficient.     

Robust computational framework for wire-mesh sensor potential field calculations

With the development of the next generation of nuclear reactor safety system codes fast underway, increased importance has been placed on enhancing physical closure correlations and amassing representative benchmark-quality experimental data for validation purposes. Wire-mesh sensors, a reputable experimental measurement technique with sufficient spatial and temporal resolution to serve such goals, and related data reconstruction algorithms have been the subject of renewed interest as researchers attempt to characterize their measurement uncertainty. To assist in such investigations, the present work establishes a comprehensive numerical framework with which to quantify the electric potential field around wire-mesh sensors. Using the finite-volume foundations of OpenFOAM, a numerical solution algorithm is developed to predict the transmitted electric current between transmitter and receiver electrodes for both homogeneous and heterogeneous electrical conductivity fields. A detailed verification against seminal numerical calculations and robust validation procedure is included to ensure the accuracy of the proposed methodology. Parametric studies of spherical bubble diameter, lateral crossing position, and spheroidal shape influence are conducted to provide preliminary insights into wire-mesh sensor operation and the suitability of various calibration approaches. Observed trends in the transmitted currents reveal overshoots relative to calibration conditions, which are fundamentally linked to the maldistributed electric potential field in heterogeneous bubbly flows. The present investigation offers a vital first step towards a comprehensive multi-physics model of multiphase flow around a wire-mesh sensor.     

Numerical simulation of detonation reflections over cylindrical convex-straight coupled surfaces

Detonation reflections over cylindrical convex-straight coupled surfaces were numerically analyzed using the density-based compressible–reactive solver DCRFoam developed on the framework of OpenFOAM-V7. The two-dimensional reactive Euler equations were adopted to calculate the reflection dynamics, considering a detailed chemical mechanism. Effects of the global wedge angle (ranging from 20° to 50°) and the radius of the former convex section (ranging from 25 mm to 125 mm) on the detonation reflections were discussed. It was founded that the original regular reflection could transform into the Mach reflection on the former cylindrical convex section for coupled surfaces with global wedge angles smaller than 50°. The peak pressures of the reflection points in the configurations of the regular reflection were much larger than those in the Mach reflection, and the increase in the wedge angle led to the increase of the average peak pressure of the reflection points in the Mach reflection on the following straight section. For a coupled surface with a global wedge angle of 50°, no Mach reflection configurations were established on the former cylindrical convex section. The existence of the convex section was proven to delay the establishment of the Mach reflection on the following straight section. For coupled surfaces with the same global wedge angles, the transition angles from the regular reflection to the Mach reflection increased with the increase in the radius.     

Dynamic two-point fluidization model for gas–solid fluidized beds

In real fluidized beds various fluidization regimes may occur simultaneously resulting in quite distinct hydrodynamic characteristics in various regions of the bed. Classical approaches, generally, use a step drag function with a single switching point to distinguish dense and dilute regimes. In the present study, a new integrated hydrodynamic model (drag and viscosity) is developed using a smooth logistic function with two switching points dividing a fluidized bed into three dense, dilute and mixed regimes which is more in accordance with reality. Gas volume fraction at minimum fluidization velocity and particle Geldart’s group are employed to decide switching between dense and dilute drag and viscosity models. A spatiotemporal dynamic algorithm is used to implement the integrated model into the open source CFD package OpenFOAM 2.1.1. Reasonable predictions of various hydrodynamic characteristics in three different experimental data sets demonstrate wide applicability of the new integrated hydrodynamic model to any fluidization regime.     

海水泵站流道非对称引水流态特性数值模拟分析

为探讨海水泵站流道非对称引水流态特性,基于OpenFOAM建立了某液化天然气接收站海水泵站流道数值模型,在利用实测数据验证的基础上,模拟计算与分析了对称和非对称引水时,流道内流速与紊动动能分布特征。模拟结果表明:海水泵站非对称引水时,水流进入前池后流速较大,在低水位下水流无法充分扩散,在流道入口处形成偏流,行进至海水泵前断面水流分布已基本均匀;非对称引水时,海水泵所在进水池各断面均匀性指数平均值高于对称引水工况,且各海水泵进水池的紊动动能平均值也小于对称引水工况;从过水断面流速分布均匀性以及紊动量级来看,非对称引水对水泵运行更有利。     

风力机气动-结构仿真平台构建与计算

为在研究大型风力机气动性能的同时考虑其结构动力学特性,基于开源计算流体力学软件OpenFOAM及气动-水动-伺服-控制软件FAST,并结合致动线方法（Actuator Line Method,ALM）实现风力机叶轮周围流场信息与结构响应间的数据交换,最终完成风力机气动-结构仿真平台FASTFOAM构建。通过该平台计算了风场中两台串列布置5 MW风力机的气动性能及结构动力学特性。结果表明：FASTFOAM平台能够快速计算出风力机的功率输出、结构响应及流场信息;风力机尾迹在发展过程中可持续与周围流场进行能量交换而使其速度亏损得以弥补;下游风力机受上游风力机尾迹影响严重,输出功率只有上游风力机的21.05%,且结构动力学响应与上游风力机不同;上游风力机和下游风力机叶轮的主要刺激频率分别为0.16和0.15 Hz。