三维计算流体力学数值模拟在重质气体扩散方面的研究综述

目前我国危险品存储存在着严重的环境风险和隐患,危险事故往往造成严重的人员伤害和财产损失,因此事故风险大气污染物三维模拟技术方面的研究具有重要意义。对CFD三维计算流体力学数值模型进行了介绍,并综述了CFD模型在危险气体扩散方面的研究现状及应用情况。

基于三维CFD分析软件CYCAS的湍流浮力流动模拟研究

严重事故中晚期,破口附近或者安全壳隔间之间的湍流浮力流动与安全壳内气体流场相互作用,直接影响安全壳内气体流场分布特性和氢气燃爆风险后果。本文应用一款三维计算流体力学(CFD)分析软件CYCAS,基于大尺寸安全壳台架流动实验PANDA OECD/SETH和PANDA HYMERES实验,开展了复杂湍流浮力流动的模拟和验证研究。结果表明,低速的湍流浮力流可在装置顶部形成分层分布,而射流在障碍物的作用下降低速度、但同时可能增强湍流脉动,有利于对分层分布的消散作用,三维CFD分析软件CYCAS可以有效模拟复杂的湍流浮力流动及其与大气流场的相互作用。在此基础上,基于某三代核电厂开展了安全壳内湍流浮力流动及其与大气流场相互作用的模拟分析。本研究表明,CYCAS软件可应用于压水堆核电厂严重事故安全壳内复杂湍流浮力流动模拟及氢气分布计算分析。

An Effective 3D-CFD Methodology for the Complementary Virtual Development of Alternative Fuels and Engine Concepts

With the aim of reducing the cost of developing internal combustion engines,while at the same time investigating different geometries,layouts and fuels,3D-CFD-CHT simulations represent an indispensable part for the development of new technologies.These tools are increasingly used by manufacturers,as a screening process before building the first prototype.This paper presents an innovative methodology for virtual engine development.The 3D-CFD tool QuickSim,developed at FKFS,allows both a significant reduction in computation time and an extension of the simulated domain for complete engine systems.This is possible thanks to a combination of coarse meshes and self-developed internal combustion engine models,which simultaneously ensure high predictability.The present work demonstrates the capabilities of this innovative methodology for the design and optimization of different engines and fuels with the goal of achieving the highest possible combustion efficiencies and pollutant reductions.The analysis focuses on the influence of different fuels such as hydrogen,methanol,synthetic gasolines and methane on different engine geometries,in combination with suitable injection and ignition systems,including passive and active pre-chambers.Lean operations as well as knock reduction are discussed,particularly for methane and hydrogen injection.Finally,it is shown how depending on the chosen fuel,an appropriate ad-hoc engine layout can be designed to increase the indicated efficiency of the respective engines.

不同数值模拟方法预测消声器传递损失的比较研究

分别采用三维有限元法(Finite element method,FEM)和三维时域计算流体力学法(Computational fluid dynamics,CFD)对消声器的传递损失进行预测,并将计算结果与文献中的实验数据进行对比,然后从计算结果的准确性,计算耗时和易用性三个方面对这两种数值方法进行比较研究。研究结果表明:无论消声器内是否存在气体流动,两种方法都能够对消声器的传递损失进行合理预测。相比之下,时域CFD法能够获得更加准确的计算结果,但计算时间消耗较长;有限元法计算时间消耗较短,但应用起来较为复杂。

喷油时刻对汽柴油双燃料燃烧影响的模拟研究

采用三维计算流体力学(CFD)模拟方法,研究了重型柴油机汽柴油双燃料模式下的燃烧和排放特性。结果表明:在重型柴油机上,汽柴油双燃料燃烧呈现先预混后扩散的两阶段放热特性;柴油喷油时刻直接影响双燃料燃烧模式的燃烧相位,喷油时刻过早或过晚都会导致预混燃烧比例的增加;在研究工况下,随着柴油喷油时刻推迟,氮氧化物(NO_(x))质量浓度先升高后降低,炭烟质量浓度的变化趋势与NO_(x)相反;在进行汽柴油双燃料燃烧模式的柴油喷油时刻优化时,应根据具体的排放和燃油耗优化目标进行参数选择。

CFD investigation of effect of nanofluid filled Trombe wall on 3D convective heat transfer

A numerical investigation was carried out on the effect of carbon nanotube(CNT)-water-nanofluid-filled Trombe wall on heat transfer and fluid flow inside a 3 D typical room.Time depending governing equations are considered with applying hot temperature at the left surface(collector) of the Trombe wall.The left wall(glazing) of the room and a square part(window) at the right wall are considered at cold temperature.The effects of Rayleigh number and the nanofluid volume fractions and the Trombe wall height on the temperature field,flow structure and heat transfer rate,are studied.The results show that the addition of nanoparticles and the increase of the Trombe wall height,enhance the heat transfer considerably and affect the flow structure and the temperature field.

Three-dimensional Computational Fluid Dynamics Modeling of Two-phase Flow in a Structured Packing Column

Characterizing the complex two-phase hydrodynamics in structured packed columns requires a power- ful modeling tool. The traditional two-dimensional model exhibits limitations when one attempts to model the de- tailed two-phase flow inside the columns. The present paper presents a three-dimensional computational fluid dy- namics （CFD） model to simulate the two-phase flow in a representative unit of the column. The unit consists of an CFD calculations on column packed with Flexipak 1Y were implemented within the volume of fluid （VOF） mathe- matical framework. The CFD model was validated by comparing the calculated thickness of liquid film with the available experimental data. Special attention was given to quantitative analysis of the effects of gravity on the hy- drodynamics. Fluctuations in the liquid mass flow rate and the calculated pressure drop loss were found to be quali- tatively in agreement with the experimental observations.

A computational analysis of the impact of mass transport and shear on three-dimensional stem cell cultures in perfused micro-bioreactors

In this study, Computational Fluid Dynamics(CFD) is used to investigate and compare the impact of bioreactor parameters(such as its geometry, medium flow-rate, scaffold configuration) on the local transport phenomena and, hence, their impact on human mesenchymal stem cell(hM SC) expansion. The geometric characteristics of the TissueFlex174;(Zyoxel Limited, Oxford, UK) microbioreactor were considered to set up a virtual bioreactor containing alginate(in both slab and bead configuration) scaffolds. The bioreactor and scaffolds were seeded with cells that were modelled as glucose consuming entities. The widely used glucose medium, Dulbecco's Modified Eagle Medium(DMEM), supplied at two inlet flow rates of 25 and 100 μl·h^(-1), was modelled as the fluid phase inside the bioreactors. The investigation, based on applying dimensional analysis to this problem, as well as on detailed three-dimensional transient CFD results, revealed that the default bioreactor design and boundary conditions led to internal and external glucose transport, as well as shear stresses, that are conducive to h MSC growth and expansion. Furthermore, results indicated that the ‘top-inout' design(as opposed to its symmetric counterpart) led to higher shear stress for the same media inlet rate(25 μl·h^(-1)), a feature that can be easily exploited to induce shear-dependent differentiation. These findings further confirm the suitability of CFD as a robust design tool.

Shape optimization of the caudal fin of the three-dimensional self-propelled swimming fish

Shape optimization of the caudal fin of the three-dimensional self-propelled swimming fish,to increase the swimming efficiency and the swimming speed and control the motion direction more easily,is investigated by combining optimization algorithms,unsteady computational fluid dynamics and dynamic control in this study.The 3D computational fluid dynamics package contains the immersed boundary method,volume of fluid method,the adaptive multi-grid finite volume method and the control strategy of fish swimming.Through shape optimizations of various swimming speeds,the results show that the optimal caudal fins of different swimming modes are not exactly the same shape.However,the optimal fish of high swimming speed,whose caudal fin shape is similar to the crescent,also have higher efficiency and better maneuverability than the other optimal bionic fish at low and moderate swimming speeds.Finally,the mechanisms of vorticity creation of different optimal bionic fish are studied by using boundary vorticity-flux theory,and three-dimensional wake structures of self-propelled swimming of these fish are comparatively analyzed.The study of vortex dynamics reveals the nature of efficient swimming of the 3D bionic fish with the lunate caudal fin.

Numerical aerodynamic analysis of bluff bodies at a high Reynolds number with three-dimensional CFD modeling

This paper focuses on numerical simulations of bluff body aerodynamics with three-dimensional CFD(computational fluid dynamics) modeling,where a computational scheme for fluid-structure interactions is implemented.The choice of an appropriate turbulence model for the computational modeling of bluff body aerodynamics using both two-dimensional and three-dimensional CFD numerical simulations is also considered.An efficient mesh control method which employs the mesh deformation technique is proposed to achieve better simulation results.Several long-span deck sections are chosen as examples which were stationary and pitching at a high Reynolds number.With the proposed CFD method and turbulence models,the force coefficients and flutter derivatives thus obtained are compared with the experimental measurement results and computed values completely from commercial software.Finally,a discussion on the effects of oscillation amplitude on the flutter instability of a bluff body is carried out with extended numerical simulations.These numerical analysis results demonstrate that the proposed three-dimensional CFD method,with proper turbulence modeling,has good accuracy and significant benefits for aerodynamic analysis and computational FSI studies of bluff bodies.