Description of velocity fields in front of exhaust axisymmetric inlets by means of new empirical equations

New empirical equations for the prediction of air velocity in a symmetry plane of freely suspended circular exhaust openings (both plain and flanged) are presented. The new equations here introduced are derived from experimental studies carried out by the authors. In consideration of the difficulty in describing simply and accurately the velocity field by means of a single equation, velocity gradients are provided along lines parallel to the opening axis (i.e. perpendicular to the plane containing the circular suction aperture). These velocity decays allow the user/designer to predict with satisfactory accuracy the air velocity also outside the hood axis, by means of easy-to-use equations.     

Air flow near an unflanged rectangular exhaust opening

Turbulent air flow fields for an unflanged rectangular opening were calculated numerically using the standard k-ε turbulence model. The accuracy of the calculations was verified by experimental laser Doppler anemometer velocity measurements and by comparison with previous empirical centre-line velocity equations. The results show that the air flow into an unobstructed exhaust hood can be predicted quite accurately provided that the calculation grid and the calculation domain are properly chosen.     

Evaluating the influence of the width of inlet slot on the prediction of indoor airflow: Comparison with experimental data

The aim of this work is to investigate the influence of two values of inlet slot width on the velocity characteristics and turbulent intensity of the airflow inside a rectangular room. The experimental data used to check the numerical results concerns a rectangular room where the air is supplied horizontally on the upper left and is exhausted through an opening on the lower right on the opposite side. The performance of three turbulence models, standard k-?, RNG k-?, and k-ω, in predicting the three-dimensional airflow in that room has also been investigated. The results for Reynolds number of 5000 are presented for dimensionless horizontal velocities and turbulent kinetic energy for two planes of the room and two inlet arrangements, one opening as large as the room and another with half of the width of the room. The results have indicated that the main features of the flow were captured by the three turbulence models investigated. On the whole, the performance of the standard k-? model was better than those of the other two turbulence models. In particular, the k-ω model performed better in the configuration with the largest air opening than in that with the smallest one, while the RNG k-? model presented the opposite behavior. The comparative study between both geometries demonstrated that for slots much smaller than the width of the room, three-dimensional effects become important.     

高大空间喷漆作业环境漆雾控制的一种新方法

利用局部静压箱和条缝型百叶排风口在污染控制区形成上送风下排风的气流组织形式.因送排风口距离小可以形成强劲的吹、吸气流,能克服冬季送热风时浮力对气流的影响,同时由于控制区域小,不污染附近的作业环境,因此可取得漆雾控制的最佳效果.     

Study on inhaled air quality in a personal air-conditioning environment using new scales of ventilation efficiency

A detailed study using computational fluid dynamics (CFD) was conducted on the influence of the difference in the effective diameters of air supply openings (air velocity, assuming the airflow rate to be constant) when using personal air-conditioning (PAC) with isothermal air currents. A new method to analyze the age of air (SVE3*) for individual supplies and the residual lifetime of air (SVE6*) for individual exhausts was developed and proposed. The study focuses on the individual supply openings and exhaust openings in a room with multiple supply openings and exhaust openings when using PAC. PAC with the larger supply opening resulted in less mixture with the surrounding air and a lower age of air than the smaller diameter, which therefore indicated better ventilation characteristics.     

Local buckling of steel plates in rectangular CFT columns with binding bars

This paper presents a theoretical study on the elastic local buckling of steel plates in rectangular concrete-filled steel tubular (CFT) columns with binding bars under axial compression. It is assumed that the unloaded edges of the steel plate are elastically restrained against rotation, whereas the loaded edges are clamped. Based on the energy method, the formulas for elastic local buckling strength of the steel plate in rectangular CFT columns under axial compression are derived, which are calibrated with the experimental results. Then the formulas are employed to study the elastic local buckling of steel plates in rectangular CFT columns with binding bars under axial compression. It is shown that the binding bars can increase the local buckling coefficient, which results in improvement of the capacity of the steel plate to resist local buckling. Finally, appropriate spacing of binding bars, appropriate limitation for aspect ratio and corresponding appropriate limitation for width-thickness ratio are suggested for rectangular CFT columns with binding bars under axial compression.     

排烟管道顶部接风管对带上盖车辆基地排烟效果的影响

提出了一种提高带上盖车辆基地机械排烟效果的方法,即设置顶部接风管.采用CFD流体力学数值模拟软件对顶部接风管的排烟效果进行研究.设置了4种开孔方式、3种顶部接风管开孔个数以及不同排烟量,通过测量带上盖车辆基地烟气层高度、盖板下方温度、能见度、CO浓度进行对比分析.结果表明:4种开孔方式排烟效果从好到差依次为顶部接风管四...     

Modification of rock mass strength assessment methods and their application in geotechnical engineering

Due to complicated structures and discontinuities in surrounding rock mass, existing empirical failure criteria cannot meet the requirements of engineering practice such as tunnels. To improve estimation accuracy on the strength of rock mass with joints, a modified chart of the Geological Strength Index using Hoek–Brown criteria was further tested to estimate rock mass strength [Lin et al. (2014) Bull Eng Geol Environ 4(73):1245–1258], and, in this paper, new strength estimation equations for jointed rock mass were then modified based on a large dataset obtained from Chinese projects. Here, standard drilling time is first introduced and described in this study, and then used as a parameter to estimate rock strength. Different empirical formulas based on joint density, rock mass classification, Hoek–Brown criteria, and elastic wave velocity are thus used to estimate rock mass strength by using data from the Jiubao tunnel. The results estimated based on different empirical formulas were similar, indicating that the modified assessment method presented in this paper can be used to estimate rock mass strength under certain circumstances. Cross-correlation of different empirical methods provides significant confidence in predicted rock mass strength calculations.     

考虑形心和剪心分离的变曲率箱梁弯扭分析

为考虑曲梁剪心和形心分离和曲率变化对曲线箱梁的影响，针对具有竖直对称轴的矩形断面变曲率箱梁，推导了考虑曲梁剪心和形心分离情况下的平衡方程，然后通过箱梁内任一点的位移方程和内力-位移关系得到考虑曲梁剪心和形心分离的变曲率箱梁的挠曲扭转微分方程，最后得到回旋曲线箱梁的平衡微分方程及其伽辽金求解。     

Impact of individually controlled facially applied air movement on perceived air quality at high humidity

The effect of facially applied air movement on perceived air quality (PAQ) at high humidity was studied. Thirty subjects (21 males and 9 females) participated in three, 3-h experiments performed in a climate chamber. The experimental conditions covered three combinations of relative humidity and local air velocity under a constant air temperature of 26 °C, namely: 70% relative humidity without air movement, 30% relative humidity without air movement and 70% relative humidity with air movement under isothermal conditions. Personalized ventilation was used to supply room air from the front toward the upper part of the body (upper chest, head). The subjects could control the flow rate (velocity) of the supplied air in the vicinity of their bodies. The results indicate an airflow with elevated velocity applied to the face significantly improves the acceptability of the air quality at the room air temperature of 26 °C and relative humidity of 70%.     

Theoretical and experimental investigation of impinging jet ventilation and comparison with wall displacement ventilation

This paper focuses on evaluating the performance of a new impinging jet ventilation system and compares its performance with a wall displacement ventilation system. Experimental data for an impinging jet in a room are presented and non-dimensional expressions for the decay of maximum velocity over the floor are derived. In addition, the ventilation efficiency, local mean age of air and other characteristic parameters were experimentally and numerically obtained for a mock-up classroom ventilated with the two systems. The internal heat loads from 25 person-simulators and lighting were used in the measurements and simulations to provide a severe test for the two types of ventilation systems. In addition to a large number of experimental data CFD simulations were used to study certain parameters in more detail. The results presented here are part of a larger research programme to develop alternative and efficient systems for room ventilation.     

Drained and undrained response of deep tunnels subjected to far-field shear loading

An analytical solution for a rectangular opening in an infinite elastic medium subjected to far-field shear stresses has been derived for drained and undrained loading conditions. A number of numerical simulations has been conducted to determine the distortion of a rectangular structure in an infinite elastic medium under far-field shear stresses also for drained and undrained conditions and when there is full slip or no slip at the ground–structure interface. The results show that the shape of the opening has a minor influence on the structure’s deformations and that full-slip conditions result in lower deformations. Undrained conditions tend to reduce distortions when the structure is more flexible than the ground, but tend to increase them for stiffer structures. A comparison between results obtained for a rectangular lined opening and for a circular lined opening are presented, and show that deformations of a rectangular structure with no-slip can be estimated from equations derived for a circular opening with an incompressible liner and also with no-slip. The effects of flexibility, slip condition at the interface, and drained or undrained loading are different for circular tunnels than for rectangular tunnels.     

Numerical study of under-ventilated fire in medium-scale enclosure

In an enclosure, as all the air inflow is consumed in burning with the excess fuel, the internal fire enters the decay phase, and such process is said flame exhaust. The complicated multistage process from an initial fire growth up to a flame exhaust followed by an external burning is investigated by means of a Large-Eddy-Simulation (LES). Turbulent combustion process is modelled by an Eddy Break-Up concept by using two sequential, semi-global steps for CO prediction. The numerical model solves three dimensional, time-dependent Navier–Stokes equations, coupled with submodels for soot formation and thermal radiation transfer. The critical fuel supply rate needed for flame to exhaust and the time period from the fuel ignition to the appearance of an external flaming in medium-scale facilities are previously obtained experimentally by Chamchine AV, Graham TL, Makhviladze GM, et al. [Experimental studies of under-ventilated combustion in small and medium-scale enclosures. In: Proceedings of the fourth international seminar on fire and explosion hazards; 2003. p. 97–107.], and the general trends predicted by the numerical model follow closely their experimental observation. This model is capable of adequately describing the essential simultaneous phenomena (flame height, soot generation, CO production, convection and radiation) occurring in a room fire. The distinct transient stages of fire development prior to flame exhaust and scenarios of the exhaust are analysed. An external burning is followed after the flame exhaust inside enclosure, and the flame height, H_f, past the ceiling is approximately in an order of the opening height. Even though the flame exhaust takes place under the critical conditions, the heat transferred from the hotter gases and the external fire source poses significant threat to people inside enclosure, and potentially induces an ignition of fuel package exposed near the opening of an enclosure.     

Novel personalized and humidified air supply for airliner passengers

The micro-environment control in an airliner cabin presented here consists in supplying each of the passengers with her/his own supply of fresh, humidified air in order to prevent possible airborne health problems and to provide local compensation for the humidity deficit. Unlike the environment control systems widely used in commercial aircraft, each of the seats in the cabin will be supplied individually with a separate airflow, which is also separately exhausted. This arrangement forms a personalized microclimate in the seat area. Essentially, focusing a personal air supply into the breathing area of the passenger works on the principle of individual seat ventilation, with the air supply and exhaust nozzles built into the back of the seat ahead. The system design, originally based on Computational Fluid Dynamics (CFD) models, has been verified by means of laboratory experiments. The results presented here have been achieved within the framework of FP6 EU Project AST5-CT-2006-030958, under the acronym SEAT (www.seat-project.org).     

Cellular confinement of tunnel sections between two air curtains

This paper compares and discusses the efficiency of various air curtains designed to ultimately operate a bilateral aeraulic confinement of a short section of a tunnel or corridor-like geometry. The tested arrangements include single- and twin-jet air curtain systems with and without air return ducts. Jet opening ratios equal to 10 and 20 are considered, with air discharge velocities ranging from 1 to 10 m/s. The facility and the experimental approach used in this work are described and justified in many details. Results are presented in terms of leakage flow rates. Information is also provided about relevant air change rates and system time constants. The global efficiency of an air curtain is greatly improved by the adjunction of an air recirculation circuit due to enhanced system stability. A critical jet exit velocity corresponding to transition from the laminar to the turbulent regime of the channel flow inside the air curtain diffuser was found. For discharge velocities larger than this critical velocity an asymptotic behaviour is observed for every air curtain tested. At the lower nozzle exit velocities, the non-recirculated twin-jet system exhibits a weird behaviour. Unexpectedly, the results show that a single jet with a given opening ratio may perform better than a twin-jet of same height with a lower opening ratio. However, the results show that the performance of an air curtain is much dependant of the conditions under which this air curtain is operated demonstrating therefore that great care should be exercised in any attempt of comparison.     

Particle Image Velocimetry (PIV) application in the measurement of indoor air distribution by an active chilled beam

We study the turbulent air flow behaviours of the attached plane jet discharged from an active chilled beam in a room using Particle Image Velocimetry (PIV). PIV is an innovative technology to study indoor air flow which began in the eighties of the last century for the measurement of whole air flow fields in fractions of a second. Here an experimental PIV system was built to reveal the structure of a turbulent attached plane jet in the entrainment process of the ambient air downstream from the jet slot. For the particle seeding in the PIV experiments, a few different particles were tested with the attached jet PIV application in a room. The results presented in this paper show the clear structure of the turbulent attached plane jet in the entrainment process after issuing from the chilled beam slot. The PIV visualisation results proved that the jet will attach to the ceiling and become fully turbulent a short distance downstream from the slot. The jet velocity vector fields show that the volume flow rate of the attached plane jet increases because of the large vortex mixing mechanism in the outer region of the jet. In three measurement cases, the air jet grows faster at a Reynolds number of 960 than at Reynolds numbers of 1320 and 1680. The calculated spreading angles in the cases with lower Reynolds numbers have similar values compared with the visualisation results.     

入口紊乱参数对室内空气分布的影响研究

文中采用计算机流体动力学（ＣＦＤ）的方法就风口入流参数对通风空调房间内空气流动和分布情况的影响作了数值研究,通过对条缝二维平面射流特性及其作为送风口的空调房间室内空气分布的数值计算结果与有关实验数据对比指出：在相当大的紊流入流参数范围内,最终的室内空气流动及平面射流特性的计算结果变化不大,藉此可以指导对室内空气流动进行数值模拟时的边界条件描述。     

腹部开孔钢筋混凝土简支梁受剪承载力计算

基于29个腹部开圆孔和42个腹部开矩形孔的钢筋混凝土简支梁的试验结果,针对不同受剪破坏形态,提出了腹部开孔的钢筋混凝土简支梁孔侧剪切破坏下的受剪承载力下限值计算公式以及上下弦杆剪切破坏下的受剪承载力计算公式,计算公式中反映了孔洞尺寸、加强腹筋、梁纵筋面积、弦杆高度、剪跨比等参数的影响。通过和国内外共计122个钢筋混凝土开孔简支梁试件试验数据的对比表明,建议公式的计算结果与试验结果吻合较好,且具有适当的安全储备。并给出了建议公式的推荐适用范围,可供实际工程设计参考。     

External flow effects on the discharge coefficients of two types of ventilation opening

Envelope flow models are commonly used in the design of naturally ventilated buildings. Such models rely on specification of the discharge coefficient, C_z, of ventilation openings, such as air vents and chimneys (stacks). Current practice is to make use of values obtained from laboratory tests under still-air conditions. These values may not be appropriate when the ventilation is due to wind, due to the external flow around the opening which is characterized by unsteadiness of both the velocity and pressure fields. Experimental tests have been carried out in a wind tunnel on two types of openings, namely a sharp-edged orifice (flush to the wall) and a long opening (chimney). Using an analytic result for the still-air case and simple dimensional analysis it is argued that the local crossflow velocity ratio, V/u, is an important parameter for the orifice and the experimental results support this (as do some simple CFD calculations). The experimental results for the sharp-edged opening are similar to earlier work on generally larger openings. For the long opening the effects of external flow are smaller. In particular, the effects are negligible when the outlet of the opening lies in the external flow. Estimates are made of the consequential uncertainties arising in envelope flow calculations for natural ventilation design.