Selection of the Relevant Turbulence Model in a CFD Simulation of a Flow Disturbed by Hydraulic Elbow——Comparative Analysis of the Simulation with Measurements Results Obtained by the Ultrasonic Flowmeter

The article is an attempt to compile the results of CFD liquid flow simulation through pipeline section containing hydraulic elbow with the results of ultrasonic flow measurements. To carry out the measurements behind the flow disturbing element (hydraulic elbow), an ultrasonic flowmeter with applied head set in accordance with the Z-type system was used. For comparative purposes, a flow simulation for 3 different turbulence models (k-epsilon, SST and SSG) was performed. It was found that with a proper ultrasonic flowmeter heads configurations, it is possible to measure the flow rate disturbed by the hydraulic elbow at any distance from the source of the disturbance. It has to use appropriate correction factor that can be determined by knowing the flow velocity profile equation. Based on comparison of CFD simulation results with experimental data, the accuracy/ purposefulness of using individual turbulence models in the case of discussed hydraulic installation was evaluated.     

板坯加热炉内常规燃烧与富氧燃烧数值计算对比分析

以某公司热轧厂板坯加热炉为研究对象,建立该加热炉内流动、传热、燃烧和板坯运动吸热过程的三维物理数学模型,运用CFD仿真技术对其进行详细的数值计算,重点对比分析了常规燃烧和富氧燃烧特性,得到了各自的炉内速度场和温度场分布规律、板坯的升温曲线以及板坯温度分布均匀性,计算结果与“黑匣子”实验测量数据吻合良好.总结出的富氧燃烧...     

Lessons from Rotor 37

INTanDUCTIONhi1992theturbomachinerycommittee0ftheIoter-nationalGasTurbineInstitute(IGTI)decidedtosetuPatestcaseforCFDcalculations.Aftersomedebateitwasdecidedthatthetestcasesh0uldbecalculated'blind',i.e.thattheexperimentalresultssh0uldn0tbemadeawilableulltilafterthesolutionshadbeensubndtted.NASA(LewisResearchCenter)offeredasuitabletestca-seintheformofahighlyloadedtransoniccompressorrot0rwhichwasthenbeingtestedwitheXtensiveuseoflaseranemometrytomeasuretheiliternalflow.Themeasurementsw…     

Computational Fluid Dynamics Simulation of Two-dimensional Natural Convection in a Fractured Porous Medium

Buoyancy induced flow is one type of flow that can occur in relation to a wide range of hydrocarbon reservoir, deep circulation of groundwater and flow around buried radioactive waste. The objective of the present study was to study the transient two-dimensional natural convection in a fractured porous medium. A computational fluid dynamics (CFD) simulation was carried out to study the velocity and temperature distribution between the two bases of a horizontal solid slab containing a fluid-filled fracture that crosses the slab. The governing equations include continuity, momentum and energy equations with Boussinesq approximation were solved simultaneously using appropriate boundary conditions. This study was confined to work out for low-Rayleigh-number flows. The simulation results were compared with experimental data to validate the accuracy of the CFD work. The CFD results were in excellent agreement with experimental data from the literature. In addition, the effective parameters such as the aspect-ratio and fracture distribution on natural convection were investigated. The results indicated that increasing the aspect-ratio of fracture caused an increase of the maximum velocity in the fracture and temperature profile in the model was affected by fractures communication. Furthermore, the effect of porous medium with a tilted fracture through it was discussed.     

Production of hydrogen and carbon by solar thermal methane splitting. IV. Preliminary simulation of a confined tornado flow configuration by computational fluid dynamics

The confined tornado flow configuration has been developed at the Solar Research Facilities Unit, Weizmann Institute of Science, as a means for protection of the window of a solar reactor from contact with incandescent solid particles in gas suspension in the reactor cavity.

The results of a computational fluid dynamics (CFD) simulation of a tornado flow confined in a simplified reaction chamber are compared in this paper with information about such a flow obtained by gas dynamics experimentation. All the information obtained by experiment was corroborated by CFD. Moreover, the CFD simulation brought to view some important unexpected features of the confined tornado flow, which are discussed in detail.     

上进风燃气灶引射性能的数值模拟

利用CFD软件对上进风燃气灶进行三维稳态流动模拟,与实测的气相色谱分析数据进行了对比,验证了数值模拟来分析引射能力的可行性。对模拟得到的速度场、温度场进行了分析,为今后的设计改进提供了依据;将CFD技术用于燃烧器设计,可缩短新产品的开发周期、降低开发成本,实现燃气具开发、设计的自主创新。     

Development of flow field design of polymer electrolyte membrane fuel cell using in-situ impedance spectroscopy

The design of a flow field channel of a polymer electrolyte membrane fuel cell (PEMFC) was investigated by computational fluid dynamic (CFD) simulation and in-situ three-channel impedance spectroscopy. To investigate the efficiency of the in-situ three-channel impedance spectroscopy method, it was adopted with a heterogeneous stack, which was composed according to three different types of flow field design. The in-situ three-channel method proved its validity by showing corresponding result with that obtained from the experiments and CFD simulation at the same experimental condition. This study demonstrates that a heterogeneous stack and in-situ three-channel impedance spectroscopy are powerful tools for predicting and analyzing the performance of a fuel cell stack.     

不同进口形式方形分离器气固两相流动的数值模拟

利用CFD计算软件Fluent6.3,采用雷诺应力模型(RSM)计算了4种不同进口形式方形分离器的气相流场及阻力,采用颗粒离散模型计算了不同粒径颗粒的运动轨迹及方形分离器的分离效率等参数.模拟预测结果表明:方形分离器内部除外旋流和内旋流主流外,还存在一些对分离效率有重要影响的局部二次流,如:分离器内排气管高度空间内的纵...     

Multi-physics CFD simulations in engineering

Nowadays Computational Fluid Dynamics (CFD) software is adopted as a design and analysis tool in a great number of engineering fields. We can say that single-physics CFD has been sufficiently matured in the practical point of view. The main target of existing CFD software is single-phase flows such as water and air. However, many multi-physics problems exist in engineering. Most of them consist of flow and other physics, and the interactions between different physics are very important. Obviously, multi-physics phenomena are critical in developing machines and processes. A multi-physics phenomenon seems to be very complex, and it is so difficult to be predicted by adding other physics to flow phenomenon. Therefore, multi-physics CFD techniques are still under research and development. This would be caused from the facts that processing speed of current computers is not fast enough for conducting a multi-physics simulation, and furthermore physical models except for flow physics have not been suitably established. Therefore, in near future, we have to develop various physical models and efficient CFD techniques, in order to success multi-physics simulations in engineering. In the present paper, I will describe the present states of multi-physics CFD simulations, and then show some numerical results such as ice accretion and electro-chemical machining process of a three-dimensional compressor blade which were obtained in my laboratory. Multi-physics CFD simulations would be a key technology in near future.     

Comprehensive investigation of membrane sorption and CFD modeling of a tube membrane humidifier with experimental validation

The humidification of PEM fuel cells is critical for their performance and efficiency and for ensuring a long durability. In most PEM fuel cell systems for mobile applications membrane humidifiers are used to humidify the fresh air. In this process, the water contained in the cathode exhaust gas is used to increase the humidity of the supply air. Despite the simple design of membrane humidifiers, the simulation of the water transfer is difficult and so far there exist hardly any precise models to calculate the absorption and desorption processes. Common approaches that use the Sherwood number to determine the sorption rates cannot account for the influence of the local water content of the membrane. This ultimately leads to an inaccurate simulation of humidifier behavior, as these models cannot consider the fact that desorption is nearly ten times faster than absorption.In this study, an empirical formula for an accurate determination of the sorption rate is derived based on experimental data. This function accounts for the different absorption and desorption rates by finding a sorption rate coefficient as a function of the local membrane water content, temperature, pressure and flow velocity.Furthermore, a CFD model is derived from the geometry of a commercially available membrane humidifier, which is also investigated on a test bench. Using the experimental data, the CFD model is validated and it is shown that the developed sorption rate formula leads to good agreements between simulations and experiments at steady-state operating points of the humidifier.     

CFD+reactor network analysis: an integrated methodology for the modeling and optimisation of industrial systems for energy saving and pollution reduction

An integrated methodology for the simulation of practical combustion systems and NO_x prediction was developed. It is based on 3D CFD simulation coupled to a postprocessor which yields reactor networks, extracted from 3D fields, as `equivalent' simplified flow models for which it is possible to use a detailed reaction kinetics. A review of some relevant application is presented to illustrate how this methodology can help in design and optimisation of industrial combustion systems towards a comprehensive improvement of the environmental performances.     

垂直轴水轮机CFD数值模拟有效性验证

CFD方法作为垂直轴水轮机水动力性能预报和分析的一种重要手段,得到了广泛的应用,但是目前,对于垂直轴水轮机CFD数值模拟的精度和可信度缺乏系统的研究,因此针对这一问题,展开了垂直轴水轮机CFD数值模拟有效性研究,探讨了湍流模型、时间步长和网格尺度对计算结果的影响,并通过与试验结果的对比,验证了CFD方法的有效性,为以后CFD方法在垂直轴水轮机性能预报方面的应用奠定了基础.     

基于中微尺度耦合模式的风电场风资源评估方法研究

针对传统风资源评估方法采用假设的入流风廓线模型而无法考虑宏观大气环流对风电场内风流动影响的问题,文章基于中尺度WRF模式和微尺度CFD模型,研究了基于中微尺度耦合模式的风资源评估方法。首先,建立基于WRF模式的中尺度数值模拟方法和基于CFD方法的微尺度风资源评估方法;其次,研究了中微尺度数值模拟方法的耦合原理,构建了从中尺度模拟结果中提取微尺度建模计算边界附近风速廓线的方法,建立了中微尺度耦合风资源评估流程;最后,通过某复杂山地风电场进行验证。验证结果表明,中尺度模拟结果可以改善微尺度CFD模型的入流边界条件,并有效降低风资源评估的误差。     

CFD study of flow in natural rubber smoking-room: I. Validation with the present smoking-room

A computational fluid dynamics (CFD) method was used to investigate the velocity and temperature distributions in an empty natural rubber smoking-room. The experimental data were used to validate the CFD model including temperatures and velocities at various positions. It was found that the results from the CFD simulation and experiments are in good agreement. Temperature difference in the room between simulation and experiment was typically in the range of 0.12–4.46 °C, and differences of average velocity at the inlet and at the outlet of the smoking-room between simulation and experiment were about 0.22 and 0.02 m/s, respectively. Furthermore, the CFD technique was employed to investigate the temperature and velocity distributions in an existing rubber smoking-room filled with rubber sheets. It was found that the temperature difference can be as high as 15 °C and that velocity distributions within the smoking-room are non-uniform. It can be concluded that the size and positions of the gas supply ducts and the ventilating lids are not optimal and that they significantly affect the circulation of hot gas in the room.     

Evaluation of cut cell cartesian method for simulation of a hook and claw type hydrogen pump

Hook and claw pumps are used for recirculation of excess hydrogen in fuel cells. Optimization of the pump design is essential. Computational Fluid Dynamic (CFD) is an effective method for performance optimization. However, it is difficult to conduct CFD simulation because of the sharp cusp of the rotor profile. Cut cell Cartesian mesh could be the solution to handle this complex and moving geometries. The aim of this paper is to evaluate ANSYS Forte for hook and claw pumps. Firstly, the conservation accuracy of the cut cell cartesian mesh is verified using an adiabatic piston cylinder case. Then, simulation results of hook and claw type pump are compared with experimental data. Finally, simulation results of air and hydrogen are compared. The results show that the CFD simulation of hook and claw pumps using cut cell cartesian mesh could provide an efficient and effective approach for the optimization of the system.     

A thermomechanical model for the analysis of disc brake using the finite element method in frictional contact

Abstract

In this work, a numerical simulation of the transient thermal analysis and the static structural one was performed here sequentially, with the coupled thermo-structural method using the ANSYS software. Numerical procedure of calculation relies on important steps such that the CFD thermal analysis has been well illustrated in 3D, showing the effects of heat distribution over the brake disc. This CFD analysis helped in the calculation of the values of the thermal coefficients (h) that have been exploited in the 3D transient evolution of the brake disc temperatures. Three different brake disc materials were selected in this simulation and comparative analysis of the results was conducted in order, to derive the one with the best thermal behavior. Finally, the resolution of the coupled thermomechanical model allows to visualize other important results of this research such as; the deformations, and the equivalent stresses of Von Mises of the disc, as well as the contact pressure of the brake pads. Following our analysis and results we draw from it, we derive several conclusions. The choice makes it possible to deliver the best brake rotor so as to ensure and guarantee the good braking performance of the vehicles.     

板坯加热炉内加热特性的数值分析

以某公司热轧厂常规与双蓄热烧嘴组合供热的板坯加热炉为研究对象,建立该加热炉炉内流动、传热、燃烧和板坯运动吸热过程的三维物理数学模型,运用CFD仿真技术对其进行详细的数值计算,得到炉内稳态的速度场和温度场分布规律、板坯的升温曲线以及板坯温度分布均匀性,计算结果与"黑匣子"实验测量数据吻合良好。本文给出的板坯加热特性计算方法为研究加热炉新工艺、优化板坯加热温度制度提供了科学依据。     

Modeling Heat Transfer and Skin Friction Frequency Responses of a Cylinder in Cross-Flow—a Unifying Perspective

The dynamic behavior of skin friction and heat transfer of a cylinder in pulsating cross-flow is investigated. Existing analytical solutions are presented as transfer functions versus frequency, known from control theory. New results for Reynolds number ranges where no appropriate model exists until now are derived. These results are obtained by the combination of computational fluid dynamics and system identification (CFD/SI). In the CFD/SI approach, time series for fluctuations of skin friction and the rate of heat transfer are generated by imposing broad-band inlet velocity fluctuations in a CFD simulation of laminar flow across a cylinder. Direct numerical simulations are conducted for mean flow Reynolds numbers between 0.1 and 40, solving the incompressible Navier–Stokes equations in a two-dimensional domain using a finite volume approach. The SI framework allows to estimate transfer functions for the response of skin friction and heat transfer to velocity fluctuations from time series data. Available analytical models for the dynamic behavior of skin friction and heat transfer usually match the simulated data up to a point, but do not give any dependence on Reynolds number. This shortcoming is addressed in this work. The identified models especially excel at Reynolds numbers of order 10.     

Detached Eddy Simulation of hydrogen turbulent dispersion in nuclear containment compartment using GASFLOW-MPI

During the severe accident in nuclear power plants (NPPs), hydrogen is generated due to the zirconium-water reaction and released from the breaks in coolant pipe forming a locally high concentration hydrogen cloud in the steam generator (SG) compartment, which plays a key role for hydrogen safety analysis in NPPs. Accurate prediction of the turbulent dispersion process of hydrogen-steam gas mixture is a critical topic for a successful simulation of the flammable cloud distribution in SG compartment. In this study, the high-fidelity temporal evolution of the hydrogen turbulent dispersion in a SG compartment is performed using the Detached Eddy Simulation (DES) based on the parallel CFD code GASFLOW-MPI to capture more detailed unsteady turbulent information. Firstly, the newly developed DES turbulence model is validated using two turbulent benchmarks, a backward-facing step turbulent flow and a hydrogen turbulent jet. The simulation results are consistent well with the experimental data. Then a SG compartment model including one steam generator, two coolant pumps, a hot leg and two cold legs is built using the specialized auto-mesh generation module. There are two modes of turbulent dispersion behavior due to the turbulent driven force in the containment, i.e. jet dominated by initial monument and plume dominated by buoyancy. The simulation result shows that the decay rate for centerline velocity obeys $1/z$ law as well as hydrogen volume fraction, indicating a turbulent jet during the steam dominated phase. There is also a relatively long potential core region which could impinge on the bottom concrete floor for the downwards jet. While the hydrogen release transfers from a turbulent jet to a turbulent plume outside the region near the inlet during the hydrogen dominated phase. Different from the turbulent jet, the centerline velocity at the plume region decays with the slope $1/z^{1/3}$, and the decay rate for the centerline hydrogen volume fraction is $1/z^{5/3}$ during this phase. Compared with the jet flow, the potential core region of the plume flow is relatively short, forming a hydrogen cloud near the inlet. The combustibility evaluation shows that the combustion clouds can be generated in the source compartment at the hydrogen dominated phase. However, they will be diluted by the following persistent steam injection from the break. This can provide technical support for the design of hydrogen mitigation system.     

A computational fluid dynamics and finite element analysis design of a microtubular solid oxide fuel cell stack for fixed wing mini unmanned aerial vehicles

Computational fluid dynamics (CFD) and finite element analysis (FEA) are important modelling and simulation techniques to design and develop fuel cell stacks and their balance of plant (BoP) systems.The aim of this work is to design a microtubular solid oxide fuel cell (SOFC) stack by coupling CFD and FEA models to capture the multiphysics nature of the system. The focus is to study the distribution of fluids inside the fuel cell stack, the dissipation of heat from the fuel cell bundle, and any deformation of the fuel cells and the stack canister due to thermal stresses, which is important to address during the design process. The stack is part of an innovative all-in-one SOFC generator with an integrated BoP system to power a fixed wing mini unmanned aerial vehicle. Including the computational optimisation at an early stage of the development process is hence a prerequisite in developing a reliable and robust all-in-one SOFC generator system. The presented computational model considers the bundle of fuel cells as the heat source. This could be improved in the future by replacing the heat source with electrochemical reactions to accurately predict the influence of heat on the stack design.