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考虑动态摩阻的管道内水气耦合瞬变流的数值模拟 总被引:1,自引:0,他引:1
输水管道系统中经常会发生水气耦合瞬变流,可能会引起异常压力波动,甚至造成爆管事故。目前针对水气耦合瞬变流的研究很少考虑动态摩阻的影响,往往会低估瞬变过程能量衰减。对此,引入一种高效准确的简化加权类动态摩阻模型,建立考虑动态摩阻的水气耦合瞬变流模型。同时,采用虚拟塞法避免了特征线法在水气交界面的动态追踪时数值插值和求解的复杂。对比分析该模型计算结果与不考虑动态摩阻模型计算结果、试验数据,发现考虑动态摩阻的模型能更好地预测气团压力衰减和耗散,与试验压力峰值更为接近;入口压力越大,初始气团越小,动态摩阻对压力波动衰减的影响越大。 相似文献
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在输/排水管道的快速填充过程中常会出现含滞留气团的复杂气—水两相瞬变流,极有可能引发异常的压力波动,从而导致严重的水力过载甚至爆管事故。目前,对于这种特殊瞬变流现象的研究基本采用一维方法或观测视角,无法准确反映气团的动态特性。为此,基于计算流体力学(CFD)模拟方法,采用5种湍流模型对该瞬变流问题进行了二维(2D)数值模拟,并将其瞬态压力、水气耦合分布模拟与试验结果进行比较。结果表明,CFD模拟方法能有效模拟水气分布及压力动态变化;标准κ-ε和标准κ-ω模型计算的最大压力误差较小,RNG模型的压力波动周期吻合度最好,两种κ-ω模型的气团模拟效果欠佳。 相似文献
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为改进利用圣维南方程处理不规则断面的方法,采用Godunov格式的有限体积法求解双曲守恒型圣维南方程。模型以水位和流量作为控制变量,利用能有效捕捉激波的HLLC近似黎曼算子计算界面通量;对于不规则的天然河道断面,采用复化Simpson公式计算相应的静水压力项;推导了离散摩阻源项的半隐格式,提高了模型的稳定性;利用TVD-MUSCL方法重构界面变量,采用改进的Euler法实现了模型空间和时间上的二阶精度。算例验证表明该模型具有良好的稳健性和实用性,能够准确模拟具有任意断面形状的天然河道中急缓交替的浅水流动。 相似文献
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抛物型断面明渠溃坝波的简化分析 总被引:1,自引:0,他引:1
利用明渠沿程抛物型断面的概化关系式,对棱柱体明渠非恒定流的控制方程进行简化分析,并应用于忽略底坡和摩阻影响的非单一湿周断面明渠瞬时全溃问题。讨论明渠湿周断面形状对溃坝涌波各水流参数的影响,在不考虑下游河床水流影响的情形下得到了坝址的水深和最大流量与湿周断面形状系数的函数关系式。 相似文献
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本文对碧口水电站压力引水系统的非恒定流情况进行了分析计算,同时得出了引水系统指定断面的压力变化过程;水轮发电机组的转速变化过程;调压井的水位波动过程及相应的最大最小值.在整个计算过程中假设较少,并由计算结果与实测结果对比可知,引水系统整个边界条件的处理较合理,尤其是水轮机边界,考虑了混流式水轮机的特性及实际关闭规律,这样所得的计算结果就更符合实际情况. 相似文献
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针对总压比20以上的某10级轴流压气机,使用一维无反射和通量守恒两类转静交界面模型进行单 通道定常数值仿真,并与试验结果对比,从交界面的守恒和无反射两方面特性分析对计算结果的影响及其机 理。结果表明:一维无反射交界面可有效消除激波反射,但无法保证交界面守恒性;对于本文研究对象,设计 点流量、峰值效率和最高压比分别偏高5%、2.6%和4% ;转静交界面通量不守恒导致的误差,会随着级数增 加而累加。通量守恒交界面虽然存在激波反射等误差,但仍可求出与试验形状接近的性能曲线,除流量偏高 3%,其余主要指标均与试验吻合。因此,计算中需综合考虑压气机的级数、负荷水平和反动度、叶尖间隙、激 波的形状和强度、超跨音叶片前缘与交界面的距离,以选择合适的交界面模型。 相似文献
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为了进一步理解压气机叶栅通道内的非定常流动结构,采用大涡模拟(LES)方法研究了来流附面层厚度和稠度变化对叶栅通道内涡系结构及总压损失系数的影响。研究表明:来流附面层增厚将导致端壁处流体的轴向动能降低,使得马蹄涡压力面分支更早地流向相邻叶片吸力面;来流附面层越厚,通道涡在叶栅尾缘沿展向抬升的高度越高,角区分离的范围也越大;叶栅的总压损失随附面层增厚而增加,附面层损失增加显著,二次流损失有所增大;稠度较低时叶栅吸力面表面存在分离,会对通道涡及角区分离产生影响;稠度增大,横向压力梯度减小,叶栅流道的速度分布更均匀,通道涡的强度和尺度减小,角区分离的范围减小;稠度增大使叶表不再分离时,总压损失显著降低,但稠度继续增大会使气流与叶片表面的摩擦损失增加。 相似文献
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Prediction of turbine blade heat transfer and aerodynamics using a new unsteady boundary layer transition model 总被引:1,自引:0,他引:1
The effects of periodic unsteady flow on heat transfer and aerodynamic characteristics, particularly on the boundary layer transition along the suction and the pressure surfaces of a typical gas turbine blade, are experimentally and theoretically investigated. Comprehensive aerodynamic and heat transfer experimental data are collected for different unsteady passing frequencies that are typical of gas turbines. To predict the effect of the impinging periodic unsteady flow on the heat transfer and the aerodynamics of turbine blades, a new unsteady boundary layer transition model is developed. The model is based on a universal unsteady intermittency function and utilizes an inductive approach that implements the results of comprehensive experimental and theoretical studies of unsteady wake development and the boundary layer flow. Three distinct quantities are identified as primarily responsible for the transition of an unsteady boundary layer: (1) the universal relative intermittency function, (2) maximum intermittency, and (3) minimum intermittency. The analysis of the experimental results and the comparison with the model prediction confirm the validity of the model and its capability to accurately predict the unsteady boundary layer transition. 相似文献
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Min-Soo Kim 《Numerical Heat Transfer, Part A: Applications》2013,63(11):835-851
In this work, a numerical study was performed to investigate the characteristics of pressure drop and heat transfer in an oscillatory flow through offset-strip fins. In the laminar regime, the flow does not oscillate, and the Colburn j and friction f factors from a steady simulation are very close to those of an unsteady simulation. The flow begins to oscillate in the transition and turbulence regimes. In these regimes, the error between the f and j values obtained from the unsteady and steady simulations becomes significant. Since an unsteady simulation is too computationally expensive, a steady simulation with a turbulence model was tested. It was found that a steady simulation with the SST(shear stress transport) k-ω turbulence model can accurately predict the Colburn j and friction f factors of an unsteady simulation. 相似文献
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煤层气生产过程中的甲烷(CH4)泄漏属于非定常流动,其计算过程复杂,往往受压力、温度等多种因素的综合影响。为了定量掌握煤层气井口位置的泄漏情况,推导了可压缩定常流动的N-S方程,结合相关假设得到了用于煤层气泄漏计算的小孔模型,考虑现实情况总结出适用于煤层气泄漏计算的经验系数。对多个煤层气区块的实际案例进行计算,并开展对比分析。结果表明,小孔模型的计算平均误差相对较小,将该模型应用于煤层气井口泄漏的计算中是可行的。 相似文献
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针对舰船燃气轮机复杂高效冷却叶片设计,基于压力修正算法建立冷却叶片一维管网设计方法;通过快速求解可压缩边界层微分方程获得叶片外换热边界,基于参数化的叶片网格生成方法,采用全隐式有限体积的固体导热求解方法,构建了冷却叶片的耦合传热模型,开发了耦合传热计算程序。对某高压涡轮动叶进行多维热耦合设计,确定冷却流路及冷气分布,通过三维气热耦合计算验证了设计方案的可行性,通过对比分析验证了多维热耦合设计方法对主要流通单元的流量、压力误差小于5%,具备较高的工程应用价值。 相似文献
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An experiment of upward gas–liquid two‐phase flow was conducted in an air–water isothermal system under atmospheric pressure. The differential pressure was measured at the fully developed section by using a variable reluctance type transducer to classify the flow patterns and their transitions. The flow behavior was observed with a high‐speed video camera. The probability density function (PDF) of the differential pressure signal was employed to identify the flow pattern. A simplified one‐dimensional flow model was proposed to clarify dominant factors affecting the formation and transitions of flow patterns. The model dealt with the gas‐component advection based on the spatiotemporal void fraction behaviors by considering the gas compressibility, the wake, and the liquid phase redistribution mechanism. The simulation results of the model indicated four kinds of the void wave patterns (ripple‐like, rectangular, distorted rectangular, and uniform wave patterns) depending on gas and liquid volumetric fluxes. These void wave patterns corresponded well to the experimentally observed flow patterns. The transitions among void wave patterns agree well with the Mishima–Ishii flow pattern map. The friction loss estimated by the present model coincides fairly well with Chisholm's empirical formula. © 2004 Wiley Periodicals, Inc. Heat Trans Asian Res, 33(7): 445–461, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20029 相似文献