带上盖开发隧道通风流场特性及射流风机偏转角度研究

带上盖开发的隧道结构复杂,通风流场紊乱,隧道运营通风能力难以得到保障。揭示这类隧道的通风流场特性,优化隧道风机布置参数具有重要意义。以广州市某珠江过江隧道工程为背景,利用数值模拟方法,探究不同风机偏转台数、偏转角度工况下隧道通风流场特性、风机升压能力。结果表明:带上盖开发隧道风机安装位置受限、复杂结构通风阻力大,导致隧道通风流场分布不均,风机升压能力较差,风机难以提供可靠的运营通风能力;带上盖开发隧道设置3台吊顶式风机时,通过合理的设置风机偏转台数和风机偏转角度,能够稳定隧道通风流场,提高平均风速,优化隧道内通风效果;当3台吊顶式风机全部偏转布置或风机偏转角度大于5°时,虽能增大未安装风机一侧的通风风速,但会导致射流分布不均,安装风机一侧风速降低,过多射流偏转也将携带更多动能撞击隧道壁面,导致射流遭受的能量损失增大,不利于隧道通风流场的稳定;采用2台吊顶式风机偏转2°~5°布置时,此时隧道内流场分布均匀,射流风机升压系数为0.7~0.8,隧道内风机射流阻力损失约28~29 Pa,可提升风机升压力,减小风机射流阻力损失,利于带上盖开发的隧道运营通风。研究结果可为优化带上盖开发隧道射流风机布置方式和保障运营通风效果提供参考。

润扬长江大桥北汊斜拉桥风流场数值模拟及压力分布特性研究

针对斜拉桥受风荷载影响较大的情况,为研究斜拉桥风压分布特性并且给润扬长江大桥北汊斜拉桥的安全运营提供数据支撑,借助FLUENT流体计算软件,并基于实测风况资料建立了实例工程的三维风流场数值模型,采取了桥面、桥塔最大风速下,风攻角分别为-5°、-3°、0°、3°、5°共5组工况,对实例工程的桥塔整体受压特性、桥梁断面风压力分布及风流场特性进行了研究。

矿井巷道风速智能感知技术研究进展

矿井通风系统智能化是推进智能矿山建设、保障矿井安全生产的关键环节,通风参数作为基础数据来源,是矿井通风系统智能化建设的重要保障。而矿井巷道风速智能感知技术发展过程中存在传感器精度及可靠性优化、传感器测风误差修正、平均风速智能快速预测、传感器布设优化等关键科学技术问题有待改善。综述了传感器技术、高精度智能风速预测等研究成果,总结了各项技术的优劣及适用范围,提出了基于PSO−GRU神经网络构建的巷道断面平均风速智能预测模型,该模型能够有效提高矿井巷道平均风速测算的精度,可为通风参数智能感知技术的发展提供理论参考。

大断面隧道风筒空间布置参数对风流流动及瓦斯扩散规律的影响研究

为优化大断面公路瓦斯隧道掌子面的风筒空间布置参数,降低掌子面瓦斯聚集超限问题,以召泸高速白兆瓦斯隧道为研究对象,通过数值模拟压入式风筒在不同附壁水平距离、垂直距离、风筒出口距掌子面的距离工况参数下的风流特性及瓦斯扩散,确定风筒合理的安装方式和布置层位。结果表明:风筒附壁平距和垂距分别为2.25m和4.5m时,掌子面附近工作区受涡流和回流作用较小,瓦斯质量分数低于0.1%;风筒出口距离掌子面的距离为25.6m工况下,在兼顾施工经济性和安全性的同时,掌子面瓦斯不易积聚,隧道中后部瓦斯质量分数低于0.071%。按照模拟结果得出的风筒合理布置参数在现场实际应用,对比结果显示两种情况下的速度和瓦斯质量分数变化规律基本吻合,充分说明了风筒空间布置参数的合理性,研究结果对大断面瓦斯隧道灾害防治具有一定的指导意义。

单洞双线隧道紧急救援站横通道风流分布研究

特长铁路隧道紧急救援站横通道内风流分布特性是救援站结构形式和防灾通风设计的基础和依据。本文针对某一单洞双线隧道平导救援站工程,深入研究紧急救援站横通道内风流分布规律,以及不同防灾通风系统和自然风对其的影响。研究结果表明,紧急救援站横通道内风速分布呈现出W型,中部和两端横通道内风速较大,沿两侧风速相对较小。自然风对横通道内风速分布有一定影响,靠近自然风入口一侧大部分横通道内风速显著增大。建议在满足人员安全疏散的基础上,可适当减小救援站中部和两侧横通道面积以及减少相应横通道内风机配置。

NUMERICAL SIMULATION ON AERODYNAMIC CHARACTERISTICS OF WINDBLAST PROTECTION AT HIGH SPEED

The computational fluid dynamics （CFD） method is used to investigate the aerodynamic characteristics of the seat/occupant with windblast protection devices. The upwind Osher scheme is used for the spatial discretisation. The detached-eddy simulation （DES） based on the Spalart-Allmaras one-equation turbulence model is ap- plied to the detached viscous flow simulation behind the seat/occupant, with Mach numbers 0.6 and 1.2 at attack angles between --10 and 30°, and at two sideslip angles of 0 and 15°, respectively. The aerodynamic characteristics of seat/occupants with and without windblast protection devices are calculated in cases of the freestream Mach numbers 0. 8 and 1.6, attack angles from 5 to 30°, and three sideslip angles of 0, --20 and --50°, respectively. Results show that simulation results agree well with experimental data. And the occupant is efficiently protected by windblast protection devices.

综采工作面巷道内瓦斯分布规律研究

为了研究综采工作面巷道内瓦斯运移规律,摸清瓦斯流动的状态,采用理论分析、数值模拟和现场试验相结合的方法,理论分析得到了工作面风流特性及瓦斯运移规律,数值模拟得到了瓦斯异常释放后工作面瓦斯浓度分布变化情况及工作面正常工作瓦斯浓度分布,然后进行现场试验,试验结果和数值模拟结果相似。研究为工作面瓦斯治理提供了技术支持。

Airflow characteristics by air curtain jets in full-scale room

A new air distribution pattern,air curtain jet ventilation was presented.The ventilation or airflow patterns and the air velocity produced by air curtain jet were investigated in detail.To identify the airflow characteristics of this novel air curtain jet ventilation system,a full-scale room was used to measure the jet velocity with a slot-ventilated supply device,with regards to the airflow fields along the vertical wall as well as on the horizontal floor zones.The airflow fields under three supply air velocities,1.0,1.5 and 2.0 m/s,were carried out in the full-scale room.The experimental results show the velocity profiles of air distribution,the airflow fields along the attached vertical wall and the air lake zones on the floor,respectively.The current experimental research is helpful for heating,ventilation and air conditioning(HVAC) engineers to design better air distribution in rooms.

Experimental study on aerodynamic characteristics of a high-speed train on viaducts in turbulent crosswinds

In this study, experiments were carried out to investigate aerodynamic characteristics of a high-speed train on viaducts in turbulent crosswinds using a 1:25 scaled sectional model wind-tunnel testing. Pressure measurements of two typical sections, one train-head section and one train-body section, at the windward and leeward tracks were conducted under the smooth and turbulence flows with wind attack angles between-6° and 6°, and the corresponding aerodynamic force coefficients were also calculated using the integral method. The experimental results indicate that the track position affects the mean aerodynamic characteristics of the vehicle, especially for the train-body section. The fluctuating pressure coefficients at the leeward track are more significantly affected by the bridge interference compared to those at the windward track. The effect of turbulence on the train-head section is less than that on the train-body section. Additionally, the mean aerodynamic force coefficients are almost negatively correlated to wind attack angles, which is more prominent for vehicles at the leeward track. Moreover, the lateral force plays a critical role in determining the corresponding overturning moment, especially on the train-body section.

Turbulence Characteristics of Swirling Reacting Flow in a Combustor with Staged Air Injection

This paper presents an experimental investigation of the turbulent reacting flow in a swirl combustor with staged air injection. The air injected into the combustor is composed of the primary swirling jet and the secon-dary non-swirling jet. A three dimension-laser particle dynamic analyzer (PDA) was employed to measure the in-stantaneous gas velocity. The probability density functions (PDF) for the instantaneous gas axial and tangential ve-locities at each measuring location, as well as the radial profiles of the root mean square of fluctuating gas axial and tangential velocities and the second-order moment for the fluctuating gas axial and tangential velocities are ob-tained. The measured results delineate the turbulence properties of the swirling reacting flow under the conditions of staged combustion.

Effect of attack angle change on hydrodynamic character of supercavitating bodies

A series of experiments has been done in a moderate-velocity cavitation tunnel to investigate the effects of attack angle change on hydrodynamic characters of supercavitation. Hydrodynamic characters of the aft section at various attack angles were compared. The investigation shows that hydrodynamic forces of the aft section are dependent of supercavity shapes at different attack angles,and the magnitude of hydrodynamic forces of the aft section varies with the change of attack angle. When the aft section is in the fully wetted case,the drag coefficient changes little. Lift and moment coefficients both increase with the increased attack angle,and the increase magnitude is not large. When the aft body planing is on the cavity boundary,the drag coefficient of nonzero attack angle is larger than that of zero attack angle,and the maximal lift and moment coefficients both vary obviously with the increased attack angle. In the case that the body is fully enveloped by cavity,the drag coefficient,lift coefficient and moment coefficient are nearly constant with the change of attack angles.

Factors Affecting Small Axial Cooling Fan Performance

Many factors such as outer diameter, hub ratio, blade numbers, shape and stagger angle affect the performance of small cooling fans. A small cooling fan was simulated using CFD software for three blade stagger angles （30.5°, 37.5°, 44.5°）and obtained the internal flow field and the static characteristics. Research indicated that the stagger angle has an obvious effect on the static characteristics of a fan. For flow rates below 0.0104 mVs, total pressure is the greatest when the stagger angle is 37.5°; flow rates higher than 0.0104 m^3/s, the total pressure is greatest when the stagger angle is 44.5° For the same flow rates, the velocity at inlet of pressure surface increases with in- creasing stagger angle, but the change of velocity on the suction surface is very small. For one model, vortices and the speed of revolution surfaces decrease with tip clearance increasing. But for other three models, increasing the stagger angle, the vortex intensity and speed of revolution surfaces at same height tip clearance increases, simultaneously, the position of vortex offset from the top of the rotor blade to the suction surface.

Effect of Tip Flange on Tip Leakage Flow of Small Axial Flow Fans

Aerodynamic performance of an axial flow fan is closely related to its tip clearance leakage flow. In this paper, the hot-wire anemometer is used to measure the three dimensional mean velocity near the blade tips. Moreover, the filtered N-S equations with finite volume method and RNG k-s turbulence model are adopted to carry out the steady simulation calculation of several fans that differ only in tip flange shape and number. The large eddy simulation and the FW-H noise models are adopted to carry out the unsteady numerical calculation and aerodynamic noise prediction. The results of simulation calculation agree roughly with that of tests, which proves the numerical calculation method is feasible.The effects of tip flange shapes and numbers on the blade tip vortex structure and the characteristics are analyzed. The results show that tip flange of the fan has a certain influence on the characteristics of the fan. The maximum efficiencies for the fans with tip flanges are shifted towards partial flow with respect to the design point of the dattun fan. Furthermore, the noise characteristics for the fans with tip flanges have become more deteriorated than that for the datum fan. Tip flange contributes to forming tip vortex shedding and the effect of the half-cylinder tip flange on tip vortex shedding is obvious. There is a distinct rela- tionship between the characteristics of the fan and tip vortex shedding.The research results provide the profitable reference for the internal flow mechanism of the performance optimization of small axial flow fans.

Experimental study of the wake characteristics of a two-blade horizontal axis wind turbine by time-resolved PIV

Wind tunnel experiments of the wake characteristics of a two-blade wind turbine, in the downstream region of 0

Experimental study on pressure and aeration characteristics in stepped chute flows

The free flow on the step surfaces has received much attention for its representative body type,flow structure,water-air two phase flow,cavitation,and many complex issues.The experiments about the time-averaged pressure and aeration concentration distribution on the step surface show that the vertical plane of steps will inevitably experience negative pressure,which must rely on adequate aeration concentration to avoid cavitation damage.However,the self-aerated flow at the head section has a relatively low aeration concentration,and the concentration of the entire steps decreases with the increasing of weir head,the minimum appears in the vicinity of the corner,and the location is close to the minimum pressure.Thus,it is necessary to set aerator in the upstream end of the step surfaces to avoid cavitation damage.

Flow Fields with Vortex in a Small Semi-open Axial Fan

In order to clarify the effect of tip clearance （TC） size on fan performance and the flow field at rotor outlet in a small semi-open axial fan, the experimental investigation was carried out. The tip diameter of test fan rotor was 180mm and test TC sizes were lmm （TC=1mm） and 4mm （TC=4mm）. Fan characteristics tests were carried out for two cases of TC size and three-dimensional velocity fields at rotor outlet were measured using a single slant hot-wire probe at four flow-rate conditions. As a result, it was found that the pressure - flow-rate characteristics curves for two cases showed almost the same tendency. However, the ensemble averaged velocity profiles along radial measurement stations of TC-4mm largely changed compared with that of TC=1mm in cases of small flow-rate condition. From the phase-locked averaging results, it was also found that the vortex existed in the rotor outlet flow field of high flow-rate condition for each TC case. Compared with the vortices for TC=1mm and TC=4mm, the vortex for TC=4mm was stronger than that for TC=1mm.

Thermo-flow characteristics and air flow field leading of the air-cooled condenser cell in a power plant

Special A-frame geometry of the air-cooled condenser cell and the complicated flow field at the exit of the axial flow fan bring on the air mal-distribution on the surface of the finned tube bundles and the deteriorated thermo-flow performances of a condenser cell. It is of benefit to the design and operation optimization of the direct dry cooling system in a power plant to investigate the thermo-flow characteristics of the condenser cell and propose the flow leading measures of cooling air. On the basis of the representative configuration of the air-cooled condenser cell in a 600 MW direct dry cooling power plant, the computa- tional models of the air side fluid and heat flows are built, in which the actual fan blade geometric details are considered. Various flow field leading ways of cooling air are presented and the thermo-flow characteristics in the A-frame condenser cell and through the finned tube bundles are compared. Results show that the flow field leading measures can result in the increased volumetric flow rate and heat rejection, thus bringing on the improved performance of the condenser cell. The improvement of thermo-flow oerformances depends upon the geometric details of the flow guiding device.

Study on air flow dynamic characteristic of mechanical ventilation of a lung simulator

As an important life support treatment, mechanical ventilation is usually adopted in clinics. With the development of the res-piratory diagnostic and treatment technologies, air flow dynamics of mechanical ventilation is usually referenced in the evaluation of pulmonary status and assessment of respiratory therapy. In order to improve the ventilation efficiency and provide a reference for pulmonary diagnostics, in this paper, a new mathematical model of mechanical ventilation system was set up. Furthermore, a prototype mechanical ventilation system for an artificial simulating lung was designed and experimentally studied. Lastly, in order to improve the ventilation efficiency and provide a reference for pulmonary diagnostics, the air flow dynamics of the mechanical ventilation system was illustrated through simulation and experimental studies. The study can be helpful to the optimization of the mechanical ventilation system.

Experimental study on the characteristics of ventilated cavitation around an underwater navigating body influenced by turbulent drag-reducing additives

In this study, a new control strategy for turbulent drag reduction involving ventilated cavitation is proposed. The configurational and hydrodynamic characteristics of ventilated cavities influenced by turbulent drag-reducing additives were experimentally studied in water tunnel. The test model was fixed in the water tunnel by a strut in the aft-part. Aqueous solutions of CTAC/Na Sal(cetyltrimethyl ammonium chloride/sodium salicylate) with weight concentrations of 100, 200, 400 and 600 ppm(part per million), respectively, were injected into the ventilated air cavity from the edge of the cavitator with accurate control by an injection pump. The cavity configurations were recorded by a high-speed CCD camera. The hydrodynamic characteristics of the test model were measured by a six-component balance. Experimental results show that, within the presently tested cases, the lengths of cavity influenced by drag-reducing solution are smaller than normal condition(ventilated cavity) in water, but the asymmetry of the cavity is improved. The drag resisted by the test model is reduced dramatically(the maximum drag reduction can reach to 80%) and the re-entrant jet is more complex after the CTAC solution is injected into the cavity. Turbulent drag-reducing additives have the potential in enhancement of supercavitating asymmetry and further drag reduction.

Prediction of Aerodynamic Noise in a Ring Fan Based on Wake Characteristics

A ring fan is a propeller fan that applies an axial-flow impeller with a ring-shaped shroud on the blade tip side. In this study, the entire flow field of the ring fan is simulated using computational fluid dynamics (CFD); the accuracy of the CFD is verified through a comparison with the aerodynamic characteristics of a propeller fan of current model. Moreover, the aerodynamic noise generated by the fan is predicted on the basis of the wake characteristics. The aerodynamic characteristic of the ring fan based on CFD can represent qualitatively the variation in the measured value. The main flow domain of the ring fan is formed at the tip side of the blade because blade tip vortex is not formed at that location. Therefore, the relative velocity of the ring fan is increased by the circumferential velocity. The sound pressure levels of the ring fan within the frequency band of less than 200 Hz are larger than that of the propeller fan. In the analysis of the wake characteristics, it revealed that Karman vortex shedding occurred in the main flow domain in the frequency domain lower than 200 Hz ; the aerodynamic noise of the ring fan in the vortex shedding frequency enlarges due to increase in the relative velocity and the velocity fluctuation.