LNG管道90°弯头压力场的数值模拟

在液化天然气(LNG)管道上安装大弯曲半径的弯头,有时会出现空间有限而无法安装的问题.针对该问题,对LNG管道内流场进行数值模拟,先用Gambit软件进行结构性网格划分,再利用Fluent软件进行模拟.边界条件设定为速度进口和压力出口,选用RNG k-ε湍流模型和SIMPLIE耦合求解方法.以规格为DN 50 mm和DN 100 mm的管道为研究对象.首先,研究流速对压力的影响,结果表明流速越大,弯头处的压力越小,从而充分说明控制流速的必要性.然后,在限定进口流速为3 m/s的前提下,对不同管径和不同弯曲半径的90°弯头处的流场进行模拟,与弯曲半径为3D的弯头相比(D为管道外直径),采用弯曲半径为1.5D弯头时,弯头处最小压力较低,但差异很小,两种规格弯头处最小压力的差值小于等于出口压力的0.28％.两种规格弯头处的最小压力均比饱和压力高0.04 MPa,不会气化.因此,安装空间不够时,LNG管道可以采用1.5D弯头;空间足够时,可以采用3D弯头.工程中所述的管道压力通常为管道轴线处的压力,对于某一管径和弯曲半径的90°弯头,不同流速时,轴线中心点和内弧中心点间压力差的比值近似等于流速比值的2次方.     

基于正压法流量校准装置用气需求的储气罐管路改造

环控试验室采用音速喷管为标准流量计的正压法空气流量校准装置,当音速喷管背压比小于临界压力比时,流量只与上游压力有关而不受下游压力的影响。因此上游供气压力波动关系到整个流量校准装置的稳定性,为减小上游供气压力的波动,对储气罐原有的并联供气管路进行改造,使其可以实现串联供气以满足流量校准装置用气需求。     

某大型集中供热热力网管线设计

结合工程实例,对大型集中供热热力网管线设计管道的设计参数进行了研究,包括无补偿管段验算、弯头设计、三通设计、补偿器验算等,同时分析了管线的设计方法,为类似工程设计积累了经验。     

某工程压力管道三通有限元分析应用

某工程的压力输水管道三通结构在干管与支管相交区域存在应力集中问题,本文采用有限元方法对干管管径DN3200、支管管径DN2200、干管与支管间夹角60°的三通结构进行了模拟分析,给出了合理的加固壁厚和加固范围,有效地降低了三通结构的应力集中。     

中外空调风管系统气动噪声计算方法的比较

对比了我国《实用供热空调设计手册》所用噪声计算方法与美国ASHRAE,英国CIBSE guide以及日本《空气调节·卫生工学便览》中所列方法。通过算例计算重点比较了中美两国手册在直管段气动噪声,弯头气动噪声,三通气动噪声和末端风口处气动噪声及各部件处噪声衰减计算上的异同。最终,除直管和弯头处噪声衰减以及声学指向性系数的计算略有出入外,主要差异集中于三通处气动噪声的计算。     

城市燃气管网的优化设计

应用最小平方和法(控制各管段流量的2次方与管段长度乘积之和为最小)，对燃气管网分配初始流量和初始压力降，从而初选管径。按控制零点压力进行管径优化。     

直埋供热管道新型三通加强结构应力分析

针对直埋供热管道压制三通处应力过大的问题，提出了一种新型三通加强结构，旨在从根本上降低压制三通相贯处的应力，提高管道敷设安全性。通过有限元数值模拟，对比分析了新型三通加强结构与普通压制三通的应力最大值与应力分布；系统研究了肋片宽度、肋片高度、外套管厚度、肋片角度等加强模型结构参数对压制三通应力最大值的影响。结果表明：新型三通加强结构能够有效减小压制三通的应力最大值，且主管管径和支主管管径比越小，应力最大值的下降效果越明显；随肋片宽度、肋片高度和外套管壁厚的增大，新型三通加强结构应力最大值减小。     

非均匀zeta电势微通道内电渗涡流的形成机理

为了探究外加直流电场下两段式直通道(上游通道和下游通道)中电渗涡流的形成机理,采用数值模拟方法研究了下游通道与上游通道的长度比、壁面zeta电势比等参数对电渗涡流形成的影响规律。结果表明:下游通道和上游通道长度比越大,下游通道与上游通道壁面zeta电势比越小,上游通道zeta电势绝对值从入口开始下降速度越快,越有利于在微通道内产生涡流。此外,在下游通道与上游通道壁面zeta电势比一定的前提下,外加电场强度和壁面zeta电势对微通道中产生的涡流大小没有影响。因此,下游通道与上游通道壁面的电渗流速度差对涡流的产生有重要影响。     

大管径气体流量计量系统

大管径气体流量计量系统石家庄市热力煤气公司针对国内现有煤气工艺和孔板流量计的技术缺陷、开发了大管径气体流量计量系统。该技术采用结构新颖的可摇孔板节流装置、多管并联、高架安装、温压补偿组合计量系统，具有量程可变。系统各部件可清洗＿在线标定、在线温度压力...     

供汽管网的节能降耗措施及效果

供汽管网是缔结供用热双方企业的生存纽带和生命网络。在管网运行管理方面采取开拓供汽市场发展新热用户、合理协调热用户负荷和调节峰谷、建立GPRS热网监控系统、加强管道维护管理等措施．提高供汽的经济效益：同时．通过采取减温器改造、旁通外压式膨胀节改造、旋转膨胀节代替横向波纹膨胀节、弯管流量计取代孔板流量计等节能改造措施,降低供汽管道压力损失0．12～0．24MPa,每年可多发电14536．30MW：建议设计时根据单位压降选择合理的管径和流速．并采用中频弯头、旋转膨胀节、弯管流量计等节能型附件,以降低管道阻力,增加供汽管网的输送距离。     

Interaction of square prisms in two flow fields

A single square prism was tested at several angles of attack in a wind tunnel in smooth and in turbulent flow. A second square prism of equal size was placed upstream with various separation distances and orientations. Proper combination of signals from sensitive pressure transducers yielded the fluctuating aerodynamic forces and moments. The mean forces and moments were determined using conventional piezometer openings in conjunction with a liquid manometer. Some error is inevitable since only three transducers were used to a side. Comparisons with available information show reasonable correspondence with the mean and fluctuating forces. Little information appears available for moments.Although the upstream prism effectively shields the downstream prism in many cases, particularly for the mean forces and moments, there are in all cases, significant values for the coefficients of fluctuating force and moment. When the two objects are offset both vertically and horizontally, particularly large mean moments occur.Use of a turbulent flow field is to be recommended for testing. Consideration of moment measurement should be of prime importance in wind sensitive structures.     

门站调压系统的影响因素分析

城市门站是连接上、下游气源的重要节点,设计时要考虑上、下游的实际运行工况及储气方式.本文从流量、压力对调压系统的影响出发,分析了不同的储气方式对门站调压系统的设计要求.     

基于FLUENT的靶式流量计数值模拟与研究

对靶式流量计的靶片进行了受力分析,得出流量计算式。采用FLUENT数值仿真软件模拟圆盘形、圆锥形、球形3种靶片的受力、流体流经靶片的压力损失与被测流体质量流量的关系。根据流量计在设计与制造中的要求,推荐采用圆盘形靶片。流体流经靶式流量计的压力损失小于其他类型流量计,量程比可达1:30,测量相对误差范围为±0.3%。     

海拔高度对公路隧道火灾烟气分布特性影响研究

高海拔地区存在大气压力低、空气密度小、含氧量低等特点,对公路隧道火灾燃烧和烟气扩散的影响与平原地区隧道有显著差异。为了得到不同海拔高度条件下公路隧道内火灾烟气扩散特性和温度场分布规律,依托米拉山高海拔特长隧道,采用FDS计算软件,对海拔0~ 6 km范围内不同海拔高度的隧道火灾进行三维数值模拟计算。分析不同海拔高度条件下火灾烟气逆流长度、隧道拱顶温度、距地面1.8 m高度处温度分布、隧道竖向温度分布等主要参数。研究结果表明:随着海拔高度的增加,火源上游区域烟气逆流长度不断减小,烟气逆流长度与海拔高度大致呈线性关系,海拔6 km情况下烟气逆流长度为平原地区的57%;与平原地区隧道相比,高海拔地区隧道火源上游区域温度较低,火源下游区域温度较高,高海拔隧道火源下游区域烟气温度降低幅度较大;火源下游区域,高海拔地区隧道竖向温度增长较快。     

超声波流量计在城市燃气管网的应用

介绍超声波流量计的工作原理,与罗茨流量计进行性能对比。探讨了超声波流量计计量精度的主要影响因素(气体组成、流场、脏污)及应对措施。     

变风量系统中环状风道的网络计算方法

提出了利用网络法计算求解变风量系统中环状风道的水力特性,构造了三通关联矩阵,以解决模拟计算中三通局部阻力系数的计算问题。在网络计算模型和算例分析的基础上,比较了环状风道和枝状风道在风量分配和阻力损失方面的区别,指出环状风道能通过调整分支风道风量分配自动实现不同支路的阻力平衡,从而降低整个风道系统的阻力损失,提高变风量系统的调节性能。     

城门洞形风道三通局部阻力系数模拟与实验

将流体流态限定在阻力平方区,对城门洞形风道三通(分流三通、封堵三通)的局部阻力系数进行模拟,将封堵三通局部阻力系数的实验结果与模拟结果进行比较。当流动处于阻力平方区时,分流三通、封堵三通局部阻力系数稳定在某个常数附近,几乎与雷诺数无关;分流三通局部阻力系数与当量粗糙度无关。     

Studies on buoyancy driven two-directional smoke flow layering length with combination of point extraction and longitudinal ventilation in tunnel fires

This paper investigates the buoyancy-driven smoke flow layering length (both upstream and downstream) beneath the ceiling with combination of point extraction and longitudinal ventilation in tunnel fires. A theoretical model is developed based on previous back-laying model with only longitudinal ventilation, with modified actual heat release rate, as well as modified upstream and downstream opposing longitudinal air flow velocities by the induced flow velocity due to point extraction. Experiments are carried out in a reduced scale model tunnel with dimensionless of 72 m×1.5 m×1.3 m. A LPG porous gas burner is used as fire source. The smoke flow layering length both upstream and downstream are identified based on temperature profiles measured along the ceiling, for different experiment conditions. CFD simulations with FDS are also performed for the same scenarios. Results show that with combination of point extraction and longitudinal ventilation, the smoke flow layering length is not symmetric where it is longer downstream than that upstream. The upstream smoke layering length decreases, while the downstream layering length increases with increase in longitudinal ventilation velocity; and they both decrease with increase in point extraction velocity. The predictions by the proposed theoretical model agree well with the measurements and simulation results.     

Investigation of vortex-induced vibration of a suspension bridge with two separated steel box girders based on field measurements

This paper investigates the vortex-induced vibration of a twin steel box girder suspension bridge with a centre span of 1650 m based on field measurements. Two ultrasonic anemometers, two tri-axial accelerometers and 52 wind pressure sensors are installed at the quarter span section. The other 20 pressure sensors are installed in another 5 sections, and each section has 4 pressure sensors. Four vortex-induced oscillation events are measured. The analytical results indicate that the vortex-induced vibration more likely occurs in a low wind speed range of 6-10 m/s, with the wind direction nearly perpendicular to the bridge line, and low turbulence intensity. The mean pressure distribution on the surface of the bridge deck is obtained and the characteristics of fluctuant pressures are analysed by proper orthogonal decomposition (POD) method. Moreover, the spatial-temporal evolution of flow around the bridge deck is investigated. The results indicate that in the beginning stage of vortex-induced resonance, the regular vortex shedding phenomena occur only in the gap of the deck and at tailing region of downstream deck; however, when in the lock-in stage, the vortex shedding is strengthened due to the dramatic vibration, and the regular vortex shedding phenomena extend to the entire lower surface of downstream deck and the tail of upstream deck, the vortex shedding regions in the gap and lower surface link together. In the lock-in range, the span-wise correlation of the wind pressure is analysed, and the correlations of wind pressure along the bridge line are very high and do not decrease with the increase in distance.     

深厚覆盖层中弱透水层厚度及连续性对渗流场的影响

中国西北地区的深厚覆盖层坝基中常存在厚度不均和不连续的弱透水层,弱透水层的厚度、不连续形式及开口大小对坝基渗流场有一定的影响,其规律需要深入研究。基于非饱和土渗流理论,借助Seep/w进行渗流求解,探讨中间位置处弱透水层的厚度及连续性对单宽渗流量和出逸坡降的影响规律,并结合工程实例进行对比分析。研究表明:单宽渗流量和出逸坡降都随着中间位置处弱透水层厚度的增加而降低;弱透水层厚度对采用半封闭式防渗墙控渗时的渗流场影响最大,悬挂式防渗墙次之,全封闭式防渗墙最小。开口在上游的弱透水层与防渗墙形成的半封闭式联合防渗体系的控渗效果最好,开口在下游的弱透水层次之,防渗墙上下游都存在开口时效果最差。单宽渗流量和出逸坡降随弱透水层上游开口长度的增加而增大,但开口长度对渗流场影响不显著,其原因在于各防渗体系下上游弱透水层仅起到微弱的隔水作用。建议防渗墙和下游弱透水层形成半封闭式联合防渗体系,避免防渗墙上下游弱透水层均存在缺口的不利情况。基于监测值和模拟值得出的误差满足规范要求,表明采用的计算方法和得出的结论皆可靠。