CFD wind tunnel test: Field velocity patterns of wind on a building with a refuge floor

This paper reports a CFD wind tunnel study of wind patterns on a square-plan building with a refuge floor at its mid-height level. In this study, a technique of using calibrated power law equations of velocity and turbulent intensity applied as the boundary conditions in CFD wind tunnel test is being evaluated by the physical wind tunnel data obtained by the Principal Author with wind blowing perpendicularly on the building without a refuge floor. From the evaluated results, an optimised domain of flow required to produce qualitative agreement between the wind tunnel data and simulated results is proposed in this paper. Simulated results with the evaluated technique are validated by the wind tunnel data obtained by the Principal Author. The results contribute to an understanding of the fundamental behaviour of wind flow in a refuge floor when wind is blowing perpendicularly on the building. Moreover, the results reveal that the designed natural ventilation of a refuge floor may not perform desirably when the wind speed on the level is low. Under this situation, the refuge floor may become unsafe if smoke was dispersed in the leeward side of the building at a level immediately below the refuge floor.     

Simulation on spread of fire smoke in the elevator shaft for a high-rise building

Spread of fire smoke in the elevator shaft of a high-rise building is influenced by many driving facts. We simulate smoke spreading in the elevator shaft, stair room, and pre-chamber with and without different supplied pressurized air. The simulation shows that smoke moves very fast in the elevator shaft. When a 12 floor high-rise building is in fire, smoke can fill up the elevator shaft in less than 1.5 min after a fire started, temperature in the elevator shaft can be higher than 187°C in 5 min, and the concentration of CO can also reach a high level. The elevator shaft has a very low visibility in less than about 100 s.     

Simulation of Wind Flow Around a Building with a k–ε Model

The three-dimensional numerical simulation of airflow around a building using a k–ε two-equation turbulence model is presented in this paper. Several cases of numerical simulation of airflow around a building are carried out to estimate the influence of mesh spacing on simulated results. The accuracy of simulations is examined by comparing the predicted results with wind-tunnel experiments. It is confirmed that numerical simulations by means of the k–ε model reproduce the velocity fields well when using fine mesh resolution. In the latter part of the paper, the simulation method is applied to predict the flow field around a building with different width-to-height ratios, under light wind conditions. Received 16 June 1999 and accepted 20 July 2000     

建筑物内火灾烟羽流和顶蓬射流诱发的空气运动盐水模拟实验研究

盐水在清水中的扩散与火灾烟气在空气中的蔓延相似，因而可用盐水的扩散来模拟火灾烟气的蔓延；同样地，由于盐水的扩散而导致的环境清水的运动也可用来模拟烟气蔓延诱发的空气运动。基于这一原理，本文用实验的方法，研究了建筑物内初起火灾产生的烟羽流和顶蓬射流所诱发的空气运动，并对走廊空气层生长规律和运动特性进行了初步的测量和分析。所得结果基本合理，对建筑物通风排烟及疏散通道设计有帮助，从而为建筑火灾环境空气的运动的实验研究开辟了新的思路，也为火灾区域模拟提供了实验依据     

A review on research of fire dynamics in high-rise buildings

Since serious fire occurred frequently in recent years, fire safety of high-rise building hasattracted extensive attention. A National Basic Research Program (973 program) of China has been setup by Ministry of Science and Technology (MOST) of China in 2012 to meet the research requirementsof fire safety in high-rise buildings. This paper reviews the current state of art of research onfire dynamics of high-rise buildings, including the up-to-date progress of this project. Thefollowing three subjects on fire dynamics of high-rise buildings are addressed in this review: theejected flame and fire plumebehavior over facade out ofthe compartment window, the flame spread behavior over facade thermal insulation materials, and the buoyancy-driven smoke transportationcharacteristicsalong long vertical channels in high-rise buildings. Prospective future works are discussed andsummarized.     

Stack effects on smoke propagation in subway stations

In fires of subway stations, the most immediate threat to passengers' life is not the direct exposure to fire, but the smoke inhalation because it contains hot air and toxic gases. To understand the mechanisms driving the motion of smoke is therefore an important issue of fire safety, and the stack effect is found to be an important mechanism having significant influence. In this paper, we compute the three-dimensional smoke flow fields under various fires happened in a representative subway station of Taipei Rapid Transit System. To clarify the mechanisms corresponding to the stack effect, a simplified three-dimensional configuration is also considered. Results indicate that, without mechanical smoke control, the stack effect plays a decisive role and is virtually the sole factor influencing the smoke movement. Because of the stack effect, most or sometimes all of the smoke will choose a vertical shaft (usually a stairwell) to evacuate, and the cross sectional area of the shaft and the location of fire determine which shaft is chosen. Present computational results show the evidences of the importance of the stack effect and provide both valuable information to the design of the passenger evacuation routes in fires as well as criteria to the design of smoke control systems of subway stations.Received: 16 January 2003, Accepted: 10 March 2003, Published online: 12 September 2003     

真实爆炸容器壳体动力响应的强度分析

运用DYTRAN编码中的欧拉计算方法,得到了作用于内径3．80m、壁厚0．09m的球形爆炸容器内壁的反射冲击波压力;再运用三维LS－DYNA有限元编码,对容器壳体在反射冲击波载荷作用下的瞬态响应进行了强度分析,着重给出了爆炸容器的几个主要开孔部位的等效应力云图。分析结果对类似工程设计和爆炸容器的安全使用具有实际意义。     

Smoke Control of Fires in Subway Stations

We investigate the effectiveness of the smoke control scheme of the Gong-Guan subway station (GGSS), a typical subway station of the Taipei Rapid Transit System and whose mechanical control systems are also standard in modern subway station design. Three-dimensional smoke flow fields under various kinds of fires are computed by computational fluid dynamics techniques and the results are illustrated on various cross-sectional planes. Results indicate that the stack effect plays a deterministic role in smoke control when a fire occurs near the stairwell; under such circumstances, no mechanical smoke control is necessary. When a fire occurs in other places, such as at the end or the center of the platform, the current mechanical control schemes of GGSS are effective; namely, the smoke can be well controlled, either it is confined to a small region or is evacuated from the station, leaving the four exits free of smoke so that the passengers can escape through them. The effect of the platform edge door (PED) on smoke control is also investigated. With the PED, the effectiveness of the present smoke control system for fires occurring on the chassis of a train, a serious fire in the subway station, increases. We also propose an innovative smoke control scheme with a PED, which turns out to be much more efficient in evacuating smoke than that currently used. This study provides both valuable information for the design of passenger evacuation routes in fires as well as criteria for the design of a smoke control system for subway stations. Received 12 August 2002 and accepted 22 October 2002 Published online 14 February 2003 RID="*" ID="*" The financial supports for this research from both the SinoTech Engineering Consultant Inc. and the National Science Council under Grant NSC 89-2212-E-002-61 are gratefully appreciated. Communicated by H.J.S. Fernando     

A NUMERICAL STUDY OF THE FLOW OVER ELLIPSOIDAL OBJECTS INSIDE A CYLINDRICAL TUBE

A numerical scheme is developed to obtain the flow field around one, two and five ellipsoidal objects inside a cylindrical tube. The scheme uses the Galerkin finite element technique and the primitive variable(u–v–p) formulation. The two-dimensional incompressible Navier–Stokes equations are solved numerically by using the direct mixed interpolation method. A Picard iteration scheme is used for the solution of the resulting system of non-linear algebraic equations. The computer code is verified by checking with known analytical solutions for the flow past a sphere. Results for the shear stress distributions along the ellipsoids, forces and drag coefficients are obtained for different geometric ratios and Reynolds numbers. Some of the intermediate computational results on the velocity fields developed are also reported.     

Numerical modelling of behaviour of reinforced concrete columns in fire and comparison with Eurocode 2

The paper describes a two-step finite element formulation for the thermo-mechanical non-linear analysis of the behaviour of the reinforced concrete columns in fire. In the first step, the distributions of the temperature over the cross-section during fire are determined. In the next step, the mechanical analysis is made in which these distributions are used as the temperature loads. The analysis employs our new strain-based planar geometrically exact and materially non-linear beam finite elements to model the column. The results are compared with the measurements of the full-scale test on columns in fire and with the results of the European building code EC 2. The resistance times of the present method and the test were close. It is also noted that the building code EC 2 might be non-conservative in the estimation of the resistance time.     

Parallel large eddy simulation of turbulent flow around MIRA model using linear equal‐order finite element method

A parallel large eddy simulation code that adopts domain decomposition method has been developed for large‐scale computation of turbulent flows around an arbitrarily shaped body. For the temporal integration of the unsteady incompressible Navier–Stokes equation, fractional 4‐step splitting algorithm is adopted, and for the modelling of small eddies in turbulent flows, the Smagorinsky model is used. For the parallelization of the code, METIS and Message Passing Interface Libraries are used, respectively, to partition the computational domain and to communicate data between processors. To validate the parallel architecture and to estimate its performance, a three‐dimensional laminar driven cavity flow inside a cubical enclosure has been solved. To validate the turbulence calculation, the turbulent channel flows at Re_τ = 180 and 1050 are simulated and compared with previous results. Then, a backward facing step flow is solved and compared with a DNS result for overall code validation. Finally, the turbulent flow around MIRA model at Re = 2.6 × 10⁶ is simulated by using approximately 6.7 million nodes. Scalability curve obtained from this simulation shows that scalable results are obtained. The calculated drag coefficient agrees better with the experimental result than those previously obtained by using two‐equation turbulence models. Copyright © 2007 John Wiley & Sons, Ltd.     

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采用经典的火羽流模型,预测了2008奥运国家主体育场典型火灾场景下火源上方不同高度处 的烟气温度;结合钢结构在不同温度条件下的强度、弹性模量参数,选取了保守的钢结构极 限环境温度值;综合上述两个方面的结果,确定了2008奥运国家主体育场钢结构中需要开展 消防保护的区域为：观众席座椅区距离座椅的垂直距离小于10.2 m的区域.     

Assessment of an Evaporation Model in CFD Simulations of a Free Liquid Pool Fire Using the Mass Transfer Number Approach

In the present paper an evaporation model is implemented and assessed in a Computational Fluid Dynamics (CFD) code named ISIS. First, the influence of the cell size and time step on the temperature field is studied via simulations with a prescribed fuel Mass Loss Rate (MLR). Then, the evaporation model is assessed using predictive simulations. The experimental scenario is a 30 cm-diameter heptane pool fire. The average fuel Mass Loss Rate Per Unit Area (MLRPUA) is predicted within 5.5% deviation from the experimental value. In addition, an analysis of the temperature and heat fluxes at the surface of the liquid, the mass transfer coefficient and the temperature inside the liquid is performed.     

Numerical study on the effect of nozzle pressure and yarn delivery speed on the fiber motion in the nozzle of Murata vortex spinning

Murata vortex spinning (MVS) is a recently developed spinning technology which utilizes high speed swirling airflow to insert twist into the yarn. The motional characteristics of the flexible fibers in the airflow inside the MVS nozzle are of vital importance to the yarn formation mechanism and properties. The fiber motion in the MVS nozzle involves fluid-structure interaction (FSI) and contact problems. In this paper, a two-dimensional FSI model combined with the fiber-wall contact is introduced to simulate a single fiber moving in the airflow inside the MVS nozzle. The model is solved using a finite element code ADINA. Based on the model, the motional characteristics of the fiber are analyzed and the effect of two process parameters - the nozzle pressure and yarn delivery speed - on the fiber motion and, in turn, the yarn tenacity is discussed. The results indicate that the fiber firstly undergoes a false-twisting process. Subsequently, its trailing end splays out and whirls within the nozzle chamber for several turns to helically wrap and make the spun yarn. The results also show that the effect of the nozzle pressure on the tenacity of the produced MVS yarn is not obvious. The increased yarn delivery speed leads to the decreased MVS yarn tenacity. The numerical results show good agreement with the experimental results provided by other researchers.     

Estimation of Temperatures in Geothermal Wells During Circulation and Shut-in in the Presence of Lost Circulation

The estimation of temperatures in and around a geothermal well during circulation, and during shut-in conditions in the presence of lost circulation is presented in this work. Estimated temperatures are compared with temperature logs measured during drilling stoppages. Temperatures were estimatted using a computer code specifically developed to account for the transient convective heat transfer due to lost circulation in the rock surrounding a well. This feature of the present code is important since wellbore simulators normally consider the heat transfer process in the rock as a merely conductive problem. The code is capable of accounting for these losses at any point in the well and application was made to the study of two Mexican geothermal wells(well LV-3 from the Las Tres Vírgenes field and well EAZ-2 from the Los Azufres field). The results show that the effect of lost circulation on the shut-in temperature profiles can be modelled satisfactorily. Research is under way to improve the present methodology.     

On the anti-plane shear of an elliptic nano inhomogeneity

The elastic field of an elliptic nano inhomogeneity embedded in an infinite matrix under anti-plane shear is studied with the complex variable method. The interface stress effects of the nano inhomogeneity are accounted for with the Gurtin–Murdoch model. The conformal mapping method is then applied to solve the formulated boundary value problem. The obtained numerical results are compared with the existing closed form solutions for a circular nano inhomogeneity and a traditional elliptic inhomogeneity under anti-plane. It shows that the proposed semi-analytic method is effective and accurate. The stress fields inside the inhomogeneity and matrix are then systematically studied for different interfacial and geometrical parameters. It is found that the stress field inside the elliptic nano inhomogeneity is no longer uniform due to the interface effects. The shear stress distributions inside the inhomogeneity and matrix are size dependent when the size of the inhomogeneity is on the order of nanometers. The numerical results also show that the interface effects are highly influenced by the local curvature of the interface. The elastic field around an elliptic nano hole is also investigated in this paper. It is found that the traction free boundary condition breaks down at the elliptic nano hole surface. As the aspect ratio of the elliptic hole increases, it can be seen as a Mode-III blunt crack. Even for long blunt cracks, the surface effects can still be significant around the blunt crack tip. Finally, the equivalence between the uniform eigenstrain inside the inhomogeneity and the remote loading is discussed.     

Numerical simulation of a low-emission gas turbine combustor using KIVA-II

A numerical study was performed to investigate chemically reactive flows with sprays inside a staged turbine combustor (STC) using a modified version of the KIVA-II code. This STC consists of a fuel nozzle (FN), a rich-burn (RB) zone, a converging connecting pipe, a quick-quench (QQ) zone, a diverging connecting pipe and a lean-combustion (LC) zone. From the computational viewpoint, it is more efficient to split the STC into two subsystems, called FN/RB zone and QQ/LC zones, and the numerical solutions were obtained separately for each subsystem. This paper addresses the numerical results of the STC which is equipped with an advanced airblast fuel nozzle. The airblast nozzle has two fuel injection passages and four air flow passages. The input conditions used in this study were chosen similar to those encountered in advanced combustion systems. Preliminary results generated illustrate some of the major features of the flow and temperature fields inside the STC. Velocity, temperature and some critical species information inside the FN/RB zone are given. Formation of the co- and counter-rotating bulk flow and the sandwiched-ring-shaped temperature field, typical of the confined inclined jet-in-cross-flow, can be seen clearly in the QQ/LC zones. The calculations of the mass-weighted standard deviation and the pattern factor of temperature revealed that the mixing performance of the STC is very promising. The temperature of the fluid leaving the LC zone is very uniform. Prediction of the NO_x emission shows that there is no excessive thermal NO_x produced in the QQ/LC zones for the case studied. From the results obtained so far, it appears that the modified KIVA-II code can be used to guide the low-emission combustion experiments.     

Water structures inside and outside single-walled carbon nanotubes under perpendicular electric field

The structures of water inside and outside(6,6),(8,8), and(10,10) singlewalled carbon nanotubes(SWCNTs) under an electric field perpendicular to the tube axis are investigated by molecular dynamics simulations. The results show that dipole reorientation induced by electric field plays a significant role on the structures of confined water inside and outside SWCNTs. Inside SWCNTs, the average water occupancy and the average number of hydrogen bonds(H-bonds) per water molecule decrease as the electric intensity increases. Because the field intensity is sufciently strong, the initial water structures inside the SWCNTs are destroyed, and the isolated water clusters are found. Outside SWCNTs, the azimuthal distributions of the density and the average number of H-bonds per water molecule around the solid walls become more and more asymmetric as the electric intensity increases. The percentages of water molecules involved in 0–5 H-bonds for all the three types of SWCNTs under diferent field intensities are displayed. The results show that those water molecules involved with most H-bonds are the most important to hold the original structures. When the electric field direction is parallel with the original preferred orientation, the density and the H-bond connections in water will be increased; when the electric field direction is perpendicular to the original preferred orientation, the density and the H-bond connections in water will be decreased.     

Down-flow and horseshoe vortex characteristics of sediment embedded bridge piers

The flow around bridge structures is a recent research topic, given the significance of bridges as basic engineering infrastructures. This study investigates the internal flow features around circular bridge piers by Particle Image Velocimetry applied both in the horizontal and vertical planes and therefore allowing for a quasi-spatial visualization of the velocity field. The temporal evolution of the vertical deflected flow at the pier front and the horseshoe vortex inside the increasing scour hole were explored resulting in the velocity and vorticity profiles. This work, therefore, provides novel insight into the complex and fascinating two-phase flow around circular bridge piers placed in loose sediment and provides an experimental data basis for advanced numerical simulation.     

On the influences of key modelling constants of large eddy simulations for large-scale compartment fires predictions

An in-house large eddy simulation (LES) based fire field model has been developed for large-scale compartment fire simulations. The model incorporates four major components, including subgrid-scale turbulence, combustion, soot and radiation models which are fully coupled. It is designed to simulate the temporal and fluid dynamical effects of turbulent reaction flow for non-premixed diffusion flame. Parametric studies were performed based on a large-scale fire experiment carried out in a 39-m long test hall facility. Several turbulent Prandtl and Schmidt numbers ranging from 0.2 to 0.5, and Smagorinsky constants ranging from 0.18 to 0.23 were investigated. It was found that the temperature and flow field predictions were most accurate with turbulent Prandtl and Schmidt numbers of 0.3, respectively, and a Smagorinsky constant of 0.2 applied. In addition, by utilising a set of numerically verified key modelling parameters, the smoke filling process was successfully captured by the present LES model.