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鉴于台阶式溢洪道的研究多集中于台阶尺寸﹑坡度﹑流态﹑消能等方面,而对台阶本身的布置形式研究很少,提出了新的过渡式台阶溢洪道布置形式,采用紊流数值模拟方法研究了不同坡度﹑不同单宽流量以及不同过渡形式下的过渡式台阶溢洪道的水力特性。结果表明,与连续等高的台阶溢洪道相比,在相同条件下过渡式台阶溢洪道台阶面上的负压区较小,消能率较高且随单宽流量的增加而增加,所提出的台阶布置形式可供相关工程参考。 相似文献
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为提高抽水蓄能电站进/出水口过栅流速均匀性,采用标准κ-ε紊流模型,对不同方案下的蛟河抽水蓄能电站进/出水口过栅水流流态进行了数值模拟。结果表明,在进/出水口其他尺寸符合常规的条件下,减少分流墩厚度(最小厚度取决于结构安全需求)可明显提高过栅流速均匀性。 相似文献
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具有交流励磁电机变速、功率解耦优点的抽水蓄能机组将在电力系统调峰、调频中发挥更好的作用,有必要研究考虑水头、流量和机组运行工况等约束条件下的可调速抽水蓄能机组运行功率能力的计算方法。首先,基于交流励磁电机电磁等效电路,考虑定、转子侧功率,推导发电和电动运行工况下的交流励磁电机接入电网侧的功率表达式;其次,考虑发电和抽水工况下水泵水轮机的工作特性,推导以水头和转速为变量的抽水蓄能机组的机械功率表达式,从而提出电动和发电工况下交流励磁抽水蓄能机组运行功率极限的计算方法和流程;最后,以某实际抽水蓄能机组参数为例,分析不同水头和转速下机组运行功率范围,并通过时域仿真结果验证所提计算方法的有效性。 相似文献
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近年来南水北调中线总干渠部分输水建筑物出现水位偏高和流态异常现象,存在输水能力下降风险,亟需评估水头损失状况,但存在建筑物内部无监测站点、工程运行尚未达到设计规模、监测数据缺乏校验等问题。采集了总干渠2022年大流量输水期间的水位、流量监测数据,开展第三方水力学原型观测,复核与校正了监测数据。提出一种使用综合水头损失系数的水头损失推算方法,对总干渠158座输水建筑物中具备分析条件的143座,推算了加大流量下的水头损失。结果表明,总干渠输水建筑物分配水头总体有剩余,分布存在明显差异。全线总计剩余水头3.05 m,其中穿黄以南段、穿黄至漳河段和漳河以北段各自剩余0.48、1.06、1.51 m,分别占分配水头的4%、13%、12%。全线有40座输水建筑物的水头损失超过分配值,其中倒虹吸31座、渡槽4座、暗渠4座、隧洞1座。 相似文献
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为验证山西省某森林公园台阶式消能泄洪槽设计的合理性,通过模型试验研究了该消能泄洪槽不同流量工况下的流态、台阶平面压力、流速分布及消能效率。结果表明,在试验流量范围内,泄槽内为跌落水流和过渡水流,掺气不明显;台阶平面压力变化范围为-9.7~24.4kPa,当流量为6m3/s时,出现最大负压9.702kPa;除#3消力池进口处外,三段台阶式消能段均为泄槽底部流速较小,对泄槽底部冲刷较小,泄槽水流表面流速最大;在不同流量下台阶式泄槽+消力池联合消能率均超过了90%,其中大部分能量消散在溢洪道台阶上。研究成果可为类似工程提供参考。 相似文献
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《中外能源》2017,(10)
针对水平井井筒积液规律认识不清导致排水采气措施针对性不高的难题,基于相似性原理,结合川西气田水平井井身结构特征研制了水平井井筒可视化模拟装置,装置采用准40mm×5mm的有机玻璃管组合连接而成,可通过改变支架系统参数模拟水平段不同型态、不同倾角条件下气井的排液情况。结合川西气田水平井气液产出特征开展了水平井水平段充满积液后卸载、气液同产、分段射孔气液同产生产过程模拟实验。结果表明,水平井水平段型态、水平段倾角对水平井最终排液率影响较小;水平段呈分层流,斜井段呈段塞流,垂直段呈环状流,液相滑脱主要发生在斜井段。现场井筒流压监测结果表明,井筒压降损失主要发生在斜井段,且压降梯度突变点位于造斜点附近,集中在造斜点上下200m范围内;明确了水平井的排液重点是斜井段的排液,为排水采气措施的针对性实施提供了指导。 相似文献
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《International Communications in Heat and Mass Transfer》2006,33(1):30-38
This paper explores the idea of selecting the flow regime in the internal structure of heat transfer systems in order to maximize their global performance under global constraints. In fluid distribution networks, we show that the pumping power requirement can be reduced by dividing a turbulent stream into several smaller laminar streams when the surfaces of the pipes are sufficiently rough. We also exemplify that for the packaging of heat-generating plates, in the range of Bejan number between 109 and 1011, spacing can be adjusted to obtain either the laminar or the turbulent regime for maximizing the heat transfer rate density. Scale analysis is used to evaluate the performance of the systems under study. 相似文献
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随着川西低渗透致密气藏不断加大水平井开发力度,水平井气井逐渐增多,水平井井筒积液成为气藏水平井开发普遍存在的难题.如果井筒内产生积液,井底回压增大,井口压力下降,产量递减较快,气井携液能力减弱,将导致井筒附近储层的含水饱和度升高,气相渗透率下降,气井难以开采,甚至最终水淹停产.应用水平井筒内流体由分层流向非分层流转变判别式,对影响水平段井筒携液的因素进行分析表明:水平段井筒倾角越大、积液高度越高,水平井筒中气液两相流型更易从层流转向非层流,水平段中的液体也就更易被气流带出.虽然井筒倾角对气体临界流速的影响较小,但井筒倾角越大,井筒内A靶点附近的积液高度越高,液体就更易被气流携带出水平段.通过实例分析也证明,水平井A、B靶点高差对气井排液有影响,B靶点比A靶点越高,越有利于井底积液从水平段排出. 相似文献
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A two-step process was adopted to model turbulent ignition that takes advantage of the possibility of decoupling the mechanical flow from chemical reaction due to the small amount of heat release before ignition. In the first step, a Reynolds stress model is employed to calculate a chemically frozen, turbulent counterflow. The second step models the ignition event by solving a joint scalar PDF equation using a Monte Carlo technique. The frozen velocity field is used to initialize the PDF model and to govern its evolution. As observed in previous DNS calculations, ignition occurs at a “most reactive” mixture fraction. The present calculations indicated that turbulence intensity had little effect on ignition temperatures, which were about 30 K higher than, but parallel to, laminar ignition temperatures. Similar results were found for both the IEM and modified Curl's mixing model. Turbulent ignition temperatures were similar to laminar ones when the mixing model was modified to account for preferential diffusion. These results are different from turbulent ignition experiments since the experiments did indicate a turbulent intensity effect on ignition of up to 35 K. These discrepancies were attributed to shortcomings in the molecular mixing models in the flows of interest where the turbulent Reynolds numbers are low. A potential source of this problem was identified as the representation of the scalar mixing frequency as a constant ratio of the scalar to flow time. 相似文献
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提出了一种可以同时作为储能介质与传热流体的新型相变微胶囊悬浮液(MPCS),设计和搭建试验台,分别在层流和湍流条件下在等热流密度的光滑圆管中对MPCS进行了强制对流换热实验,研究了悬浮液浓度、流量、泵送功率和加热速率对其流动及传热特性的影响。结果表明:对于质量分数为5%的MPCS,当微胶囊中相变材料分别处于固体、固体-液体和液体状态时,对应的努塞尔数平均增大了23.9%、20.5%和9.1%;与纯水相比,MPCS作为在热力系统应用的传热流体可以实现强化传热,但是需要在传热实验中控制好相变过程才能使MPCS的传热性能优于水。 相似文献
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A photovoltaic-powered water pumping system, employing an induction motor pump, capable of supplying a daily average of 50 m3 at 37-m head has been developed. The system was installed on a desert well in Jordan, where: the average solar radiation amount to 5.5 kW h/m3/day, to provide the Bedouins living in the well area with drinking water.A mathematical model to enable testing the system performance by computer simulation was developed. This model allows the representation of motor torque in function of speed (and slip) at different supply frequencies, as well as the flow rate and efficiency of the system in function of supply frequency and pumping head.Prior to its installation on the desert well, the system performance, in accordance with frequency and head, was thoroughly tested in the laboratory. As illustrated in this paper, simulation and laboratory testing results are well matched. At constant pumping head, the flow rate is proportional to the supply frequency of the motor. At constant flow rate, the pumping head is proportional to the supply frequency squared only in the range below the peak efficiency of the pump. For higher flow rate values, a special algorithm based on the experimental results could be developed.Higher system efficiency is achievable at higher frequency. It is advisable to operate the motor pump at the nominal frequency, flow rate and head corresponding to maximum efficiency.Long-term field testing of the system shows that it is reliable and has an overall efficiency exceeding 3%, which is comparable to the highest efficiencies reported elsewhere for solar powered pumps. 相似文献
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Forced-convective internal cooling of a horizontal equilateral-triangle cross-sectioned duct 总被引:1,自引:0,他引:1
An experimental determination of the steady-state forced convection from the internal surfaces of a horizontal, uniformly heated electrically, equilateral-triangle cross-sectioned duct with sharp corners has been undertaken. The average Nusselt number
D, using the hydraulic diameter as the characteristic physical dimension, is a constant if the flow in the duct is laminar, but a function of the air's Reynolds number, when the flow is turbulent. Non-dimensional correlations, which can be used for predicting the value of the steady-state rate of convective heat transfer from such a triangular duct into the airflow, have been deduced, viz.
D = 3·25 for laminar flows, i.e. ReD < 1450; and
D = 0·012 ReD0·83 for turbulent flows, i.e. ReD ≥ 1450. 相似文献
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S.C. Kakarantzas I.E. Sarris N.S. Vlachos 《International Journal of Heat and Mass Transfer》2011,54(15-16):3347-3356
MHD free convection of a liquid metal is studied in a closed vertical annulus in which the upper and bottom walls are adiabatic while the cylindrical walls are kept at different temperatures. The flow is driven by two mechanisms; the temperature difference between the two cylindrical walls and the volumetric heating. A constant horizontal magnetic field is also imposed resisting the fluid motion. The laminar and turbulent regimes of the flow are assessed by performing three-dimensional direct numerical simulations. The results show that in the absence of the magnetic field, turbulent flow is developed in most of the cases, while as the magnetic field increases the flow becomes laminar. The highest temperature is found in the upper-central part of the annular cavity when the fluid is heated volumetrically, resulting in the creation of two convection currents as the hot fluid ascends in the central part and descends close to both colder walls. The Hartmann and Roberts layers developing near the walls normal and parallel to the magnetic field, respectively, are found to be responsible for the loss of axisymmetry of the present flow. 相似文献
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Phani Krishna Kadiyala 《传热工程》2018,39(2):98-106
Heat transfer from a moving surface with uniform wall temperature due to impingement of series of slot jets has been investigated numerically. In the present paper, transition–shear stress transport model has been used for numerical simulations, which can predict the heat transfer in laminar as well as turbulent flows. This model is adopted here to study the transport phenomenon and predict the transition from laminar to turbulent flow seamlessly under different surface velocities. The present model with stationary surface is validated with the correlation given by Martin for series of slot jets. It has also shown good agreement with existing data for both laminar and turbulent slot jets, and is further studied to understand the heat transfer under wide range of flow conditions and the effect of surface velocity on flow regime. The range of Reynolds number is from 100 to 5,000, whereas surface velocity varied up to six times the jet velocity at the nozzle exit. It has been observed that at high surface velocities the heat transfer from the moving wall is more than stationary case. The transition from laminar to turbulent regime is found to be starting at a Reynolds number of 400 and turns completely turbulent at a Reynolds number of 3,000. Q-criterion is used to confirm the transition zone by observing the breaking of vortices at higher Reynolds number. 相似文献
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J.H. Nie 《International Journal of Heat and Mass Transfer》2004,47(22):4713-4720
Laser-Doppler velocity measurements adjacent to the bounding walls of three-dimensional (3-D) backward-facing step flow are performed for the purpose of mapping the boundaries of the reverse flow regions that develop in this geometry (adjacent to the sidewalls, the flat wall and the stepped wall) as a function of the Reynolds number. The backward-facing step geometry is configured by a step height (S) of 1 cm, which is mounted in a rectangular duct having an aspect ratio (AR) of 8:1 and an expansion ratio (ER) of 2.02:1. Results are presented for a Reynolds number range between 100 and 8000, thus covering the laminar, transitional and turbulent flow regimes. The boundaries of the reverse flow regions are identified by locating the streamwise coordinates on a plane adjacent to the bounding walls where the mean streamwise velocity component is zero. The size of the reverse flow regions increases and moves further downstream in the laminar flow regime; decreases and moves upstream in the transitional flow regime; and remains almost constant or diminishes in the turbulent flow regime; as the Reynolds number increases. The spanwise distribution of the boundary line for the reverse flow region adjacent to the stepped wall develops a minimum near the sidewall in the laminar flow regime, but that minimum in the distribution disappears in the turbulent flow regime. Predictions agree well with measurements in the laminar flow regime and reasonably well in the turbulent flow regime. 相似文献
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《International Communications in Heat and Mass Transfer》1994,21(1):65-74
Flow pattern transition from stratified-smooth to stratified-wavy has been usually identified with a condition of neutral stability, where destabilizing effects are due to the inertia of the two-phases. It is shown that this is indeed the case when instability is approached with laminar gas phase. However, when the upper gas phase is turbulent, a destabilizing term appears due to dynamic interaction of the turbulent flow with the perturbed free interface. At the transitional range from laminar to turbulent flow regime the evolution of wavy pattern is not predicted by stability condition and coincides with the laminar/turbulent flow regime transition. 相似文献