过渡流下双圆柱横向距对壁面传热特性的影响

为了优化圆柱下游壁面的流动传热特性,对串列双圆柱对壁面的传热特性进行数值分析。采用基于复合网格系统的计算方法,研究了不同串列双圆柱横向距(P)对壁面传热特性的影响。研究结果表明P对壁面的传热强化效果有显著影响。P存在1个临界值5 D,小于该临界值时,后面圆柱对前面圆柱剥离后的不规则尾流具有稳定作用,传热能力较弱;大于该临界值时,无法达到洗刷效应与流体受迫加速的叠加作用,不利于传热强化。在Re=200,C/D=1.0工况下,P为5 D时壁面的传热强化效果最优。     

高雷诺数下阵列四圆柱绕流流动形态数值模拟

本文利用CFD(计算流体动力学)软件FLUENT对阵列四圆柱进行了数值模拟。选取的湍流模型为RNG k-ε模型,雷诺数为Re=2.07×10~5,模拟了不同间距比(S/D=0.3、0.6、1.0、1.3、1.6、1.9)及风攻角(α=0、15°、30°、45°)情况下四圆柱绕流的流动形态。结果表明:S/D=0.3时流动形态为单体模式,S/D0.3时上游圆柱后形成不完整的涡脱结构,S/D0.6时上下两排圆柱后逐渐形成独立的涡脱结构,且α=15°、30°、45°时的流动形态较α=0时复杂。     

线形布置三圆柱脉动气动力及风压分布特性试验研究

为了给线形布置三圆柱结构的抗风设计提供参考，通过刚性模型测压风洞试验研究了线形布置三圆柱在不同风向角(0°～90°)和间距比(1.2～4.0)下的脉动气动力及风压分布特性，并与单圆柱的结果进行了对比分析。研究结果表明：线形布置三圆柱的脉动气动力特性可按间距比大致分为小间距比(1.2≤L/D≤2.0,L/D为相邻圆柱中心距与圆柱直径之比)、中等间距比(2.0相似文献   

亚临界雷诺数下线形布置三圆柱的平均气动力特性

为了给线形布置三圆柱结构的平均风荷载取值提供参考，通过刚性模型测压风洞试验研究了线形布置三圆柱在不同风向角和间距比下的平均气动力特性，并与单圆柱的结果进行对比分析。试验雷诺数为6.4×10⁴,风向角α和间距比L/D(相邻圆柱中心距与圆柱直径之比)的范围分别为0°～90°和1.2～4.0。研究结果表明：线形布置三圆柱的平均气动力特性可按间距比大致分为极小间距比(1.2≤L/D<1.4)、小间距比(1.4≤L/D<2.5)、中等间距比(2.5≤L/D<3.5)和大间距比(3.5≤L/D≤4.0)四类；三圆柱的平均阻力系数在极小间距比和小间距比时主要表现为减小效应，中等间距比时在α<60°时表现为减小效应，在α>60°时表现为一定的放大效应，大间距比时下游两圆柱在α≤30°时表现为减小效应；三圆柱的平均升力系数在一定风向角范围内表现为非零值，该风向角范围与间距比密切相关。     

直角三角形排列倾斜三圆柱绕流数值模拟

本文采用计算流体动力学软件FLUENT对雷诺数Re=1.03×10~5情况下的直角三角形排列倾斜三圆柱(由上游直立圆柱、上游横风向倾斜圆柱与下游顺风向倾斜圆柱组成)绕流进行了数值模拟,得到了倾斜角α=0°、8°、15°三种情况下,在间距比S/D=3.5时的三圆柱表面压力系数C_P分布及阻力系数C_D,以及倾斜角α=15°情况下不同展向高度处的C_P与C_D。结果表明:上游直立圆柱与横风向倾斜圆柱不受轴向风速分量影响,展向C_P分布及C_D变化不大,三维特性不显著,但直立圆柱由于受到下游圆柱的影响,C_D较单圆柱略有减小;下游顺风向倾斜圆柱受到遮挡效应与轴向风速分量的综合作用,C_P及C_D的三维特性较为明显,C_D在S/D=4.0时出现突变。     

低雷诺数下五圆柱绕流的数值模拟研究

基于四叉树自适应网格,采用有限体积法求解二维不可压粘性N-S方程,对X型排列和十字型排列的五圆柱绕流进行了模拟,计算均在Re=100的条件下进行.在文中给出了升力系数及阻力系数随圆柱间距比和排列方式变化的规律,并结合不同间距比下的流动特征进行了分析.计算结果表明,在不同的间距比下,五圆柱绕流存在三种不同的流动形式;在同一间距比下,十字型布置和X型布置的流动形式则既有类似之处又有各自的特点.在不同排列方式下,升阻力系数随圆柱间距比的变化规律有较大不同.     

微细通道换热器空气侧性能的模拟及优化分析

采用数值模拟方法对微细通道换热器空气侧传热和流动特性进行了研究,得到了在不同迎面风速、百叶窗间距、肋片间距和百叶窗角度下换热器的传热和流动特性,并分析了换热器结构参数对其传热及流动性能的影响。在数值模拟基础上对换热器结构参数进行优化,并采用JF综合性能系数法对各种优化方案进行了综合评价分析。     

纵向翅片管排在隧道内自然对流换热模拟研究

对具有6根纵向翅片管的冷管排在地铁隧道内的自然对流换热现象进行了数值模拟,流态假设为层流,分析了不同管排与隧道侧面墙壁距离L(L/d=1,2,3,4,5)和相邻两翅片管管心距离S(S/d=2,3,4,5,6)对冷管排自然对流流动和换热的影响。模拟结果表明:隧道侧壁与冷管排的相互作用对自然对流流动与换热产生了引流效果。在墙距L和管距S较小时,空气流动处于劣势,管排与空气的换热处于削弱状态。随着墙距L的增加空气流动逐渐增强,但引流效果逐渐减弱,使得管排的平均对流换热系数在L/d=2时到达峰值。随着管间距S的增加空气流动逐渐增强,使气流下游翅片管受上游翅片管尾流的削弱作用逐渐减弱,当S/d=5时管排的平均对流换热系数到达峰值。     

百叶窗翅片传热特性的数值模拟

为研究百叶窗翅片空气侧的传热和流动特性,建立了换热器的三维模型并进行数值模拟,通过计算得出传热与阻力特性与实验关联式吻合较好;同时对不同百叶窗倾角和百叶窗间距的模型进行了计算,比较发现倾角为27°的百叶窗翅片的传热最好;翅片间距不同,对应的传热最好的百叶窗间距不同;阻力随着百叶窗倾角和百叶窗间距的增大而增大.计算结果为换热器优化设计提供了依据.     

泥石流软基消能排导槽流速与消能特性试验研究

排导槽内泥石流流速是排导槽设计时需要考虑的重要参数之一。使用泥石流原样进行室内模型实验,探究了不同泥石流重度、肋槛间距、排导槽坡度下泥石流在排导槽内流速的变化规律和排导槽肋槛对泥石流的消能规律。研究得到如下结论:试验条件下,泥石流排导槽对泥石流流速的降低率随泥石流重度变化不大;泥石流在排导槽内平均流动速度随泥石流重度的增加而减少,随泥石流排导槽坡度的增大而增大,随肋槛间距的增加而增加;泥石流在排导槽内消能率呈现如下规律:单个肋槛平均消能率随泥石流重度的增大而增大,随排导槽坡度的增大而增大。不同肋槛间距下,泥石流在排导槽内整体消能率随肋槛间距的增大而降低,单个肋槛平均消能率随肋槛间距的增大而增大。根据本文研究相关成果,在进行泥石流排导槽设计时,通过合理设计排导槽横断面、坡度、肋槛等参数,能有效控制泥石流流速,达到降低泥石流冲击破坏的目的。     

利用排水流动的物理规律确定排水管流量

本文介绍利用排水管排出污水时出管口时的流动的物理轨迹,利用自制的简单测量设备测定其相关的参数,利用数学方程解算出污水流出管口时的初速度,再测定管口污水的截面积,进而计算出排水管的全天流量。为城市截污提供设计依据。     

Study of flow pattern in open channel flow passages

The uniform flow distribution in the upstream side of open channel flow passages is to be ensured at different flow rates. This finds critical importance in many industrial applications including chemical plants and nuclear reactors. This paper describes the method for achieving the uniform flow pattern in open channel flow passages with the aid of stream equaliser plates of different lengths and porosities.     

High-rate overland flow

Recommended loading rates for treating raw domestic wastewater by overland flow are 6.3–15 cm wk⁻¹. Information provided in the literature yields little insight regarding the upper range of hydraulic loading rates that could be effectively treated by overland flow. Therefore, field investigations were conducted to evaluate the performance of the overland flow system at overland flow rates from 0.95 m³ day⁻¹ m⁻¹ width of slope (13 cm wk⁻¹ to 4.15 m³ day⁻¹ m⁻¹ (57 cm wk⁻¹).Preliminary treated municipal wastewater was pumped to overland flow slopes, each approx. 3.7 m wide and 36.5 m long. The slope of each plot was 2.5%. The cover crop consisted of a mixture of ryegrass, bluegrass and fescue grass. The plots were operated for 2 years at six different hydraulic loading rates.Effluent BOD₅ concentration averages varied from 6 to 11 mg l⁻¹. The reduction of influent BOD₅ concentration ranged from 87 to 93%. Mean effluent suspended solids values were from 6 to 9 mg l⁻¹ with reductions of influent concentrations of 91–95%. Hydraulic application rate had little effect on percent BOD₅ or suspended solids removal.Total phosphorus reductions were minimal at all hydraulic application rates due to limited soil water contact.Ammonia concentration in the effluent ranged from 1 mg l⁻¹ NH₃-N at the 0.95 m³ day⁻¹ m⁻¹ (13 cm wk⁻¹) applied flow rate of 11.7 mg l⁻¹ NH₃-N at the 4.15 m³ day⁻¹ m⁻¹ (57 cm wk⁻¹) loading rate. Ammonia and nitrogen reductions decreased as the applied flow rate increased. Consequently, lower overland flow rates are necessary for nitrogen removal.The use of high-rate overland flow could potentially reduce the land necessary for this form of land application, if nutrient removal was not a local concern.     

Ideal cavity flow

By using the Schwartz-Christoffel transformation ideal fluid flow over a rectangular cavity is investigated. The use of Jacobian elliptic integrals and functions enables the streamlines and fluid velocity to be determined. A design chart is presented whereby the dimensions of the cavity uniquely define a required constant. Since an analog exists between ideal fluid flow and steady-state heat flow it is shown how the lines of heat flux and isothermals may be found.     

A new simple water flow system for accurate continuous flow tests

A new simple water flow system is described. The system can be used for rates of flow ranging from millilitres to litres, and has proved to be accurate and easy to handle.     

考虑非达西渗流半径的气井不稳定渗流产能模型

为研究低渗、储层厚度和孔隙度较大气藏的气井非达西渗流边界影响,基于气井非达西渗流区域的划分,推导了非达西渗流半径和非达西渗流压力损失计算公式,根据气体不稳定渗流基本微分方程,建立了基于非达西渗流边界的气井不稳定渗流产能计算新方法,结合气井实例,进行了产能计算和影响因素分析。研究结果表明:在开采的初期阶段,非达西渗流半径和非达西渗流压力损失迅速下降,对气井产能的影响较大;考虑非达西渗流半径计算的产能高于非达西渗流半径趋于无穷大的产能;随着基质渗透率的减小以及储层厚度和孔隙度的增加,考虑非达西渗流半径与非达西渗流半径趋于无穷大,2种条件预测的日产气量差值越大。     

Air flow through cracks

The pressure flow characteristics of a number of full-scale model cracks, representative of real leakage paths, have been measured. The crack flow equations developed by Etheridge [1] have been verified over a wider range of parameters. The authors suggest a quadratic relationship: ΔP = A·Q+B·Q² which follows from the same flow theory as the Etheridge solution, to replace the ubiquitous power law as a practical fit to pressurisation data. Unlike the power law, the quadratic coefficients A and B can be directly related to crack parameters, and a simple graphical method is given to enable the prediction of crack leakage areas.     

Impact of flow path length and flow rate on phosphorus loss in simulated overland flow from a humic gleysol grassland soil

In this overland flow simulation experiment, the relationships between flow path length, flow rate and the concentration of different P fractions were investigated. Overland flow was simulated using a 3 mx0.12 m laboratory flume. To remove the impact of rainfall on P lost in overland flow, simulated rainfall was not used during these experiments. Instead overland flow was generated by pumping water into the flume at the surface of the grass sod. The experimental setup allowed for the variation in flow path length and flow rate between and during experimental runs. The results demonstrated that an increase in flow path length caused an increase in Total Dissolved P (TDP), Dissolved Reactive P (DRP) and Total Reactive P (TRP) concentration in overland flow (p<0.01) while an increase in flow rate resulted in a decrease in the concentration of these P fractions in overland flow due to dilution (p<0.01). Total P (TP), Particulate P (PP) and Dissolved Organic P were not affected by the variables tested during this study. When flow path length was increased in conjunction with flow rate, there was an increase in TDP, DRP, and TRP concentrations despite the impact of greater dilution. The results indicate that variations in flow path length during a rainfall event may play a role in determining the concentration of dissolved P fractions in overland flow at field scale.