Experimental estimation of the head loss coefficient at surcharged four-way junction manholes

ABSTRACT

The head loss caused by the surcharged flow from four-way junction manholes is the main cause of increased flood damage in urban areas. The flow pattern significantly varies depending on the inflow conditions of the inlet pipes and constitutes the flow conditions of a four-way junction manhole, three-way junction manholes, and middle manholes. Therefore, the head loss changes with various manhole shapes must be analyzed. In this study, physical model study apparatus was prepared. Various flow rate conditions were selected by changing the flow rate ratios of the inlet pipes at 10% intervals. The head loss coefficients were also estimated. A head loss coefficient range diagram was generated based on the results. A head loss coefficient empirical formula that considers all flow conditions for surcharged four-way junction manholes is proposed. The proposed equation should be applicable to the design and assessment of drainage systems with varying inlet pipe flow rates.     

Hydraulic design aspects for supercritical flow in vortex drop shafts

ABSTRACT

Vortex drop shafts, as special sewer manholes, operate optimally if an adequate energy dissipation is guaranteed and the integrity of the structural components is safeguarded. The results of an experimental study on a vortex drop shaft with supercritical inflow are discussed herein. The hydraulic behaviour of the spiral inlet, the vertical shaft and the dissipation chamber is described. Based on detailed flow observations, useful recommendations for designing these structures are provided. It is demonstrated that a relation adopted for supercritical bend flows provides a reliable estimation of the maximum wave height along the inlet. A procedure for predicting the rotational flow angles and the velocity distribution along vertical shafts with swirling flows is developed. Water levels and pressure measurements in the dissipation chamber are further analysed to identify maximum forces acting on the chamber invert and to derive preliminary design equations.     

Hydrological assessment of flow dynamic changes by storm sewer overflows and combined sewer overflows on an event-scale in an urban river

In addition to assessing the impacts of water quality changes in urban rivers caused by storm water sewer overflows (SWO) and combined sewer overflows (CSO), the extent to which flow dynamics are changed by these structures must be understood in order to define hydrological assessment criteria to guide sustainable water management strategies as required by the European Community (EC) Water Framework Directive. In this study, the quantitative impacts of SWOs and CSOs on the flow dynamics of an urban river and their variability are investigated. For four single runoff events, hydrological measurements were accomplished in the River Dreisam, upstream and downstream of the city of Freiburg, in southwest Germany. As the catchment is widely free of urban areas upstream of the city, comparison with downstream locations allowed quantification of Freiburg's effects on the changes in the hydrograph on an event scale. The proposed hydrological parameter—flow acceleration, peak discharge, and discharge dosage—were shown to be appropriate to assess the impacts of SWOs and CSOs on flood hydrographs in urban rivers.     

Numerical investigation of the flow in a kitchen hood system

This study presents the results obtained when Computational Fluid Dynamics is applied to calculating the flow in a domestic kitchen hood at operating conditions. Special emphasis has been placed on parametric modeling of the geometry to permit the rapid modification of fundamental parameters, such as the number of blades and the twisting angle. The governing equations (mass, momentum, energy and turbulence) have been solved using the commercial code, fluent. The predicted characteristic curves of the hood ventilator based on the dimensionless flow and load coefficients have been built, and they are shown to be in good agreement with the experimental data. Finally, the hood model has been incorporated into a full-scale kitchen to predict airflow conditions in this space.     

Numerical investigation on hydraulic and gas flow response of MSW landfill cover system comprising a geosynthetic clay liner under arid climatic conditions

Municipal solid waste (MSW) landfill cover systems are designed to minimize the infiltration of rainwater into waste and to mitigate the biogas emissions to the atmosphere. In the present study, the efficacy of such a landfill cover system consisting of a Geosynthetic clay liner (GCL)in mitigating the hydraulic flow and gas emissions under arid climatic conditions was investigated critically. For this purpose, the water retention curve (WRC), hydraulic conductivity function, and gas flow characteristics of the chosen GCL were studied through experimental methods in the laboratory. The unsaturated transient state seepage analysis utilizing coupled hydraulic and gas flow mechanisms was performed in the study to assess the performance of the cover system. The results obtained from the experiments were used as input parameters. The effect of drying/desiccation and the self-healing nature of GCL due to climatic changes were also analyzed by exposing the GCL directly to the climatic boundary for one year. It was observed that the GCL present in the chosen cover system effectively functions as a hydraulic barrier in arid climatic conditions. However, during the summer and winter seasons, an increase in gas flow from 0.02 g/h/m² to 24.7 g/h/m² was observed, probably due to the drying anddesiccation of GCL. Interestingly, due to the self-healing nature of the GCL, gas flow through the cover system was substantially reduced to 0.02 g/h/m² during the rainy season. The effect of drying was more pronounced when the GCL was exposed to the climatic condition, leading to an early gas breakthrough and an increase in gas flow from 0.02 g/h/m² to 957 g/h/m². The percolation through the cover system remains considerably low throughout the year, mostly due to the unsaturation and low hydraulic conductivity in GCL. A cumulative percolation close to 0.1 m³ was observed at the end of one year in arid climatic conditions.     

地下水流动对埋地换热器影响的模拟研究

通过求解含水层中地下水流动的二维能量方程,分析了地下水流动对U型埋地换热器与周围土壤换热的影响,并与非含水层情况进行了比较。模拟结果表明,地下水流动显著影响埋地换热器周围的土壤温度场。与粘土层相比,埋地换热器在含水层内土壤温度变化较小,到达稳态时间较短。埋地换热器周围热作用半径,沿上游方向较小且很快达到稳态,而沿下游方向上的热作用半径基本与运行时间成正比关系。地下水流速越大,埋地换热器周围介质的平均温度越低,这有利于夏季排热工况。     

变流量系统水力稳定性分析

随着变流量系统的广泛应用。对如何提高中央空调水系统稳定性提出了新的挑战。本文采用依次关闭各支路。然后计算未关闭支路流量的方法．分析和比较了不同控制方式下变流量系统的水力稳定性。结果表明。在没有设置动态平衡措施的变流量系统中,随着系统末端电动二通阀的调节,会对其他末端水力工况产生影响。使之发生动态水力失调,影响空调区域的舒适性。提出了几种减小系统水力失调。提高系统稳定性的措施。     

A flow microcalorimetry investigation of the toxicity effects induced by aliphatic alcohols in a heterogeneous aerobic culture

An extensive investigation of the influence of aliphatic alcohols on the metabolic activity of a heterogeneous culture has been carried out using flow microcalorimetry as a monitoring technique. The response of the culture to the addition of alcohols (n-C₃ to n-C₈, t-C₄) has been examined for the microorganisms under endogenous conditions and substrate saturation conditions, and IC₅₀ values were determined for each state. For the n-alcohols, the inhibitory behavior was further examined through systematic variations of substrate and alcohol concentrations; the results yield inhibition patterns which show specific behavior both as function of alcohol concentration and alcohol chain length. Generally, the toxicity results obtained with the heterogeneous culture follow rather closely those found in homogeneous cultures. However, the initial effect of alcohols at low concentration show marked variations among various types of culture or when compared to other reference systems.     

高黏改性沥青高温流动特性及感温性能研究

采用2种不同的高黏添加剂复配SBS改性沥青制备高黏改性沥青,通过流动模型及黏温曲线方程对高黏改性沥青的流动特性与感温性能进行研究。结果表明:采用流变指数来描述改性沥青的流动性具有良好的相关性,Ⅰ型、Ⅱ型高黏改性沥青和SBS改性沥青的流变指数随着温度的升高逐渐增大,温度为175℃时已接近牛顿流体;活化能研究表明,Ⅰ型高黏改性沥青的活化能较大,抵抗外界变形的能力较强,SBS改性沥青次之,Ⅱ型高黏改性沥青活化能相对最小。     

考虑不同成桩方式单桩特性的颗粒流数值模拟

采用基于离散单元法的颗粒流数值技术对砂土中(无黏聚力)设置就位后单桩在使用阶段的承载特性进行了数值模拟。对应工程中的挤土桩与非挤土桩,按照桩设置的不同方式研究并对比了静压沉桩方式与预埋式两种不同单桩在就位后的工作特性,对两种成桩方式下桩–土–筏板的共同作用特性也略作了比较。分析中,克服传统的连续介质力学模型的宏观连续性假设,研究加载过程中桩体力学行为表现与桩周土体的细观结构参数反应的联系,增进了对桩基工程承载特性与土体渐进破坏演变过程的深入理解。此外,将模型试验与数值模拟结果作了对比分析,桩端荷载–位移曲线特征有较好的一致性。     

惰性气体灭火系统喷嘴流量特性的实验研究

通过对喷嘴流量系数的研究,明确了喷嘴流量系数的物理意义和影响因素。流量系数不随压力变化而改变。通过分析喷嘴入口压力与质量流量,明确了某一压力下喷嘴质量流量仅与静压力和温度有关。通过对4种不同规格、型号、尺寸的喷嘴进行以IG541为气源的单瓶组、单喷嘴流量特性试验,测得喷嘴的压力——时间曲线和温度——时间曲线,对试验结果进行分析得出:在忽略误差的情况下,喷嘴压力——质量流量曲线不随温度变化而改变。由此得到测量喷嘴入口处静压力和总压力计算喷嘴质量流量的方法。根据上述结论,计算得出喷嘴的喷射率与流量系数成正比,参照标准喷嘴,设计喷嘴的喷射率可通过设计喷嘴的流量系数求得,为工程设计计算提供依据。     

室外风对火焰特征影响的数值模拟研究

为研究高层建筑或超高层建筑中室外风在玻璃破碎后对火焰特征的影响,运用FDS数值模拟方法,对风速为0～24m/s的17个自由燃烧算例进行了模拟研究,拟合了适用于较大室外风速条件下的火焰长度及其倾角计算公式,并与Dfaveri模型、Drysdale模型进行了对比分析。结果表明:室外风速增大会使火焰长度及其向上风向倾斜的角度减小,但会使火焰向下风向倾斜的角度增大。     

基于能量集聚原理的全泄爆间室型结构内爆炸荷载计算

全泄爆间室型结构（简称“全泄爆间室”）内发生爆炸时,冲击波峰压值和冲量值因其在结构内多次反射而增高,精确计算非常困难,为此,进行了大量的试验研究。根据试验波形和数据可知,室内受约束空气冲击波不断反射、冲击,成为能量不断集聚的合成波和密齿形集团冲击波,从而增大了间室内爆炸破坏力。基于能量集聚原理,引进能效系数η,以ηQ表示增大的爆炸药量,并用试验数据控制精度,提出了全泄爆间室结构内爆炸荷载计算方法。     

对杭州市公路交通流量特征的研究与分析

通过对近几年杭州市公路交通流量特征进行的分析,指出本地区交通结构的状况和发展趋势,为公路建设规划、建设决策和公路养护管理提供了参考意见。     

平行流换热器干工况下应用的可行性分析

阐述平行流换热器的构造特点以及传热与流体流动特性,分析其在干工况下使用时存在的差异和问题。与常用翅片管式换热器进行性能对比,可知平行流换热器代替翅片换热器在干工况下运行具有一定的可行性。     

综合物探方法在泥石流调查中的应用

泥石流是地质灾害的主要类型之一,如何准确地探测泥石流层的厚度,对于判断泥石流的规模与地质灾害评价非常重要.本文简要叙述了探地雷达和直流电阻率测深法的探测原理,由于泥石流与基岩的物性有差别,因此应用以上两种物探方法探测泥石流理论上是可行的.通过探地雷达和直流电阻率测深法在泸定县泥石流区域的应用实例分析,证明了采用综合物探...     

对集中空调冷却水系统变流量的思考

回顾了《暖通空调》近年来所发表的若干关于集中空调冷却水系统变频节能方面的论文，认为集中空调冷却水系统变流量运行对空调系统的节能具有积极意义，但节能收益有待于深入研究。     

地铁站台疏散通道断面风场特性研究

针对规范中对地铁站台疏散通道断面（楼扶梯口处）仅给出风速限制的现状,采用计算机模拟和现场测试相结合的方法,对断面风场特性进行研究。站台公共区火灾排烟工况下,该断面风速呈现出沿高度方向的典型分层现象,自下而上分别为边界区、主流区、衰减区、回流区。人员活动大部分位于主流区,其内部风速为 3~6 m/s,有利于抑制烟气蔓延、补充新鲜空气。研究发现由于向下气流的渐扩效应在该断面顶部产生小面积回流,其对火灾烟气的潜在卷吸风险值得注意,并应在风速测试中判别气流方向。     

Numerical modeling of the flow conditions in a closed-circuit low-speed wind tunnel

A methodology for numerically simulating the flow conditions in closed-circuit wind tunnels is developed as a contribution to the general philosophy of incorporating Computational Fluid Dynamics (CFD) in wind tunnel design and testing and to CFD validation studies. The methodology is applied to the full-scale Jules Verne climatic wind tunnel in which experimental data have been obtained. Due to the specific features of this closed-circuit wind tunnel, the conventional CFD modeling approach, in which only the flow in the wind tunnel test section is modeled, is inadequate. To obtain accurate results the entire wind tunnel has to be modeled. In the numerical closed-circuit wind tunnel, the conventional flow inlet and outlet are replaced by a single “fan boundary condition”. Special attention is given to the theoretical background and the practical implementation of this type of boundary condition in the CFD model. The numerical model is validated for the case of an empty wind tunnel and for the case in which a block-type building is placed in the test section. It will be shown that this methodology can generally reproduce the wind tunnel measurements of mean velocities with an error equal to or less than 10% despite the occurrence of multiple flow separations upstream of the test section. This provides perspectives for the future use of this methodology as a tool for wind tunnel design and testing and for CFD validation purposes.     

开采条件下海河流域平原区浅层地下水数值模拟研究

本文利用地下水数值模拟系统(GMS),建立了能反映海河流域平原区地下水含水层结构及其水流特性的大区域水文地质概念模型和地下水流模型,重点研究了在无开采井条件下地下水开采强度时空分布的特征,模拟了平原区1965~2005年41年间的地下水流场及漏斗的演变过程,综合分析了海河流域平原区浅层含水层长期开采条件下地下水系统的演变过程以及地下水开采带来的影响。同时,对所建立的地下水数值模型就流场、漏斗变化以及水文地质参数等多方面进行了识别和验证。采用经过率定和验证的模型,预测分析了水资源配置制定的地下水限采方案,为南水北调实施后对海河流域地下水的修复作用以及其它可能的影响提供了可靠的分析手段和措施。