基于混合平面法的轴流式水轮机内三维湍流数值模拟

通过求解由κ-ε双方程湍流模型封闭的三维时均N-S方程对轴流式水轮机内部四个典型工况的全三维紊流场进行了计算,并采用“混合平面”法处理转轮与导叶问动静耦合流动的参数传递和相互干扰问题。捕捉到了轴流式水轮机内部压力分布和速度分布等重要的流动信息,在此基础上计算了四个工况下转轮的水力效率。结果表明,该方法能够较为准确地预测出轴流式水轮机转轮与导叶间的总性能参数及内部流场结构,所得到的结果对进行轴流式水轮机的水力设计或改型优化设计等研究具有重要的指导意义。     

水泵水轮机转轮内部三维紊流流场计算与性能分析

水泵水轮机转轮可以在正反两个方向上旋转，用一个转轮分别实现水泵和水轮机工况的运行。在设计阶段提前预知转轮在两种工况下的流场以及能量特性对于提高水泵水轮机的设计水平和运行质量具有重要的意义。本基于三维Navier-Stokes方程和标准k-ε模型，采用贴体坐标和交错网格系统，用SIMPLEC算法分析了水泵水轮机转轮中的三维紊流流场。对比了转轮在水轮机和水泵两种工况下的流场，同时讨论了转轮的能量特性。     

三峡水轮机转轮固液两相三维紊流计算及磨损预估

本在两流体模型的基础上，使用贴体坐标的有限体积法，利用有哥氏力修正的κ-ε-Ar，两相流紊流模型建立了水轮机转轮内部的三维泥沙固液两相紊流计算模型。模型中求解了考虑压力对固粒相影响的时均Reyno1ds动量方程，并利用泥沙相的速度和浓度分布，数值计算转轮的泥沙磨损。用该模型计算了三峡水轮机转轮内部的三维泥沙固液两相紊流流动，数值预估了三个不同工况转轮的泥沙磨损情况．计算表明汛期三峡水轮机转轮将有一定的磨损，磨损的主要部位是叶片正面靠近出口和下环面的三角区。靠近山水边的磨损速率约为1．3mm/年。     

可实现性k-ε模型在水轮机流场计算中的应用

本文针对目前水轮机转轮内部流场计算中存在的偏工况计算困难的问题，探讨了一种不同于标准k-ε模型的可实现性k-ε模型（Realizablek-ε在水轮机偏工况计算中的应用。文章首先对该模型的优点进行了分析。然后针对某混流式转轮进行了计算，计算与实验结果比较表明，二者在设计工况附近时十分接近；在小开底小流量下，对转轮的主要特征的预测也是成功的。但小开度下计算值与实测值之间的差别也表明，在水轮机偏工况计算中，该湍流模型有待进一步改进。     

水轮机转轮的三维粘性流数值计算及其结果分析

针对比转速ns为290的混流式水轮机转轮进行三维粘性流数值计算，并对计算结果作了初步分析．计算中，紊流模型采用目前国内外广泛使用的k-ε模型，流速与压力的迭代修正采用SIMPLE法．共对包括设计工况在内的8个工况点进行了流场数值计算及水力性能分析．计算表明，设计工况下的流速分布最为均匀，叶片进口边基本上为无冲角绕流，效率也最高；随着水头的提高，正冲角增加，最后在叶片背面进水边后靠上冠处产生漩涡区；而当水头相对设计水头降低时，负冲角增加，最后在叶片正面进水边后靠上冠处产生漩涡区．经分析认为这些漩涡区是非设计工况下叶道涡产生的根源，亦是水力性能下降的主要原因．此外，通过对压力系数分布曲线的分析，确定了局部低压区，从而为改型设计提供了依据．计算结果不仅能详细给出水轮机转轮内的流速和压力分布，而且能给出水轮机转轮的水力性能预估值，本计算所依赖的计算软件可成为水轮机转轮开发研究的重要手段．     

轴流式水轮机能量特性预测分析

采用数值计算方法研究轴流式水轮机的能量特性。计算模型建立在雷诺平均的Navier-Stokes方程的基础上，采用k-ε紊流模型,至水轮机流道内部流动进行三维紊流计算。计算不同的工况下机组的特性，绘制转轮在不同桨叶角度下的定桨特性曲线，在此基础上得出转轮的协联曲线及综合运转特性曲线，从而对机组的能量性能作用合理的判断。轴流转桨式水轮机运行效率较高的关键在于，其活动导叶和转轮桨叶之间具有最佳可调性能的协联关系。目前对协联线的绘制有包络线法和最高效率点法，采用何种方法值得进一步研究，针对具体电站机组，应该在最优效率区并偏重安全运行特性来绘制。     

龙滩水电站700MW机组转轮水力计算及低水头运行稳定性优化分析

为研究龙滩水电站700 MW水力发电机组转轮运行的综合性能,采用三维湍流数值模型对转轮进行了数值计算和性能预估.通过数值计算结果与试验结果的对比分析,为龙滩水电站转轮在各工况尤其是低水头工况的安全稳定运行提供了参考依据,并提出了改善机组稳定运行的建议和优化措施.     

长短叶片混流式水轮机三维非定常流数值模拟

为探究长短叶片混流式水轮机在不同导叶开度下运行时内部水流流动的特点,基于流场数值模拟的计算方法对长短叶片混流式水轮机进行了全流道三维非定常湍流计算。结果表明,在不同开度下,转轮与导叶交界面处压力脉动主频皆为转轮转频与叶片数的乘积,且在小流量工况下主频振幅最大。当水轮机在小流量工况下运行时,尾水管涡带呈螺旋形,且绕转轮转轴顺时针旋转,与转轮旋转方向相同;当水轮机在额定工况下运行时,尾水管无涡带产生;当水轮机在大流量工况下运行时,尾水管涡带呈细长的圆锥形。     

水轮机转轮固液两相三维紊流计算及磨损预估

本文在两流体模型的基础上，使用贴体坐标的有限体积法，利用有科氏力修正的κ-ε-Ap两相流紊流模型建立了水轮机转轮内部的三维泥沙固液两相紊流计算模型。模型中求解了考虑压力对固粒相影响的时均Reynolds动量方程，并利用泥沙相的速度和浓度分布，数值计算了转轮的泥沙磨损。为了验证模型的可行性，用该模型计算了刘家峡HL001-25模型水轮机转轮内部的三维泥沙固液两相紊流流动，数值预估了转轮的泥沙磨损并与磨损试验结果进行了比较。     

水轮机转轮内部的三维固液两相紊流计算

利用K-ε-AP两相紊流模型和SIMPLEC法计算水轮机转轮内部的三维固液两相紊流.计算结果给出了水轮机转轮内部的三维固液两相流动的主要流动参数，例如，连续相(液相)和离散相(固相)速度，两相速度滑差，固液两相流动下的压力分布等。     

基于CFX的离心泵内部流场三维数值模拟

基于三维不可压缩流体的N-S方程和标准k-ε湍流模型,采用隐式修正SIMPLE算法,利用CFX软件,对离心泵装置进行全流场三维数值模拟,共计算额定转速下30～80 m3/h流量范围内8个工况点。对比分析小流量工况、设计工况和大流量工况下泵装置流态和压力分布,并分析叶片表面静压,揭示内部流动规律,所得结果对预测水力性能,提高水泵效率及进一步结构优化具有重要的参考价值。     

NUMERICAL INVESTIGATION OF CAVITATION PERFORMANCE OF SHIP PROPELLERS

The cavitation performance of propellers is studied based on viscous multiphase flow theories. With a hybrid grid based on Navier-Stokes (N-S) and bubble dynamics equations, some recent validation results are presented in this paper in the predictions of the thrust, the torque and the vapor volume fraction on the back side of propeller blade for a uniform inflow. The numerical predictions of the hydrodynamic performance and the sheet cavitation under several operating conditions for two propellers agree with the corresponding measured data in general. The thrust and the torque are plotted with respect to the advance rate and the cavitation number. The cavitation performance breakdown is closely related to the strong sheet cavitation around propellers. The models with parameters modified are shown to predict the propeller cavitation well.     

Informational Entropy: a Failure Tolerance and Reliability Surrogate for Water Distribution Networks

Evolutionary algorithms are used widely in optimization studies on water distribution networks. The optimization algorithms use simulation models that analyse the networks under various operating conditions. The solution process typically involves cost minimization along with reliability constraints that ensure reasonably satisfactory performance under abnormal operating conditions also. Flow entropy has been employed previously as a surrogate reliability measure. While a body of work exists for a single operating condition under steady state conditions, the effectiveness of flow entropy for systems with multiple operating conditions has received very little attention. This paper describes a multi-objective genetic algorithm that maximizes the flow entropy under multiple operating conditions for any given network. The new methodology proposed is consistent with the maximum entropy formalism that requires active consideration of all the relevant information. Furthermore, an alternative but equivalent flow entropy model that emphasizes the relative uniformity of the nodal demands is described. The flow entropy of water distribution networks under multiple operating conditions is discussed with reference to the joint entropy of multiple probability spaces, which provides the theoretical foundation for the optimization methodology proposed. Besides the rationale, results are included that show that the most robust or failure-tolerant solutions are achieved by maximizing the sum of the entropies.     

NUMERICAL STUDY OF CAVITATION ON THE SURFACE OF THE GUIDE VANE IN THREE GORGES HYDROPOWER UNIT

Large-area erosions such as rust and obvious cavitation were found on the surface of the guide vane in Three Gorges hydropower units. A numerical explanation of the cavitation is given in this article. At first, based on the characteristic performance curves of the prototype hydro-turbine supplied by ALSTOM together with the actual operating conditions, an operating point is chosen for numerical analysis using the Reynolds-Averaged Navier-Stokes (RANS) equations. The flow passages from the inlet of the spiral case to the outlet of the draft tube are included in the computational domain. The results show that the static pressure on the guide vane surface is much higher than the critical pressure of cavitation. Secondly, a tiny protrusion on the guide vane surface is considered and the problem is simplified to a 2-D problem to study the local detailed flow near the guide vane surface. The protrusion is 0.5 mm in height and is 5.0 mm in width. On the basis of the results of RANS simulations, the 2-D problem is studied using the Large Eddy Simulation (LES). It is shown that there exists a region in which the static pressure reaches a level below the vapor pressure of the water. Thirdly, a cavitation model is included for the 0.5 mm protrusion case and another tiny pit case, with a tiny pit 0.3 mm in depth and 1.0 mm in width. The results show that vapor bubble exists at the protrusion entrance and the pit exit as the low pressure regions.     

Modification and Re-calibration of the Simulation Model of Lake Nasser

Abstract

In 1981, a mathematical simulation model for Lake Nasser (SMLN) was developed to test different hydrologic conditions and operation policies of the Aswan High Dam (AHD). At that time, AHD had been operating for around 12 years. Over the thirty years of the dam operation, the Egyptian water resources managers experienced cycles of floods and droughts. Also, data and information about the hydrologic parameters of the lake as well as the dam performance were accumulated. This by itself constitutes a good reason for re-calibrating of the SMLN. The 1998–1999 flood, which manifested the need to reconsider the dominant operation policy, also called for the adjustment and re-calibration of the SMLN or at least to retest its accuracy. This paper describes the effort carried out to recalibrate this model using few parameters and adjust its original mathematical formulation. Elements of the mass balance equation of the lake, which are uncertain and at the same time seem to have significant impact, have been used in the modification and re-calibration. The presented results show, in many cases, an improvement in the model performance and accuracy when compared with the original version calibrated in 1981. Nevertheless, these results should not be considered a final step in improving the model performance. Actual measurements of evaporation rates and piezometric heads of the groundwater around the lake may be used to formulate new and better loss equations     

基于弱可压缩理论的射流泵流场数值预报

应用弱可压缩流体控制方程和大涡模拟湍流模型，采用MacCormack的预估一校正方法对射流泵内流场(二维)进行了数值模拟。经过对不同射流泵运行工况的计算，都取得了令人满意的预报结果。研究表明，弱可压缩流动方程能代表低马赫数时的真实流动现象，且方程具有双曲性质易于数值求解。数值模拟结果可为改进射流泵性能提供依据。     

Sensitivity of reservoir operation performance to climatic change

The potential impacts of changing climatic conditions on the operational performance of water resource systems was investigated in this paper. A multi-site streamflow generation model was used to synthesize potential monthly flow sequences reflecting two different sets of climatic conditions. The generated data were subsequently employed as input to a reservoir operation model that was used to determine the reservoir response to the inflow resulting from the implementation of the reservoir operating policy. The performance of an example reservoir system, the Shellmouth Reservoir located in the Canadian province of Manitoba, was evaluated and compared for the two sets of conditions. The operational performance was evaluated in terms of the reliability of the system for meeting the three purposes of the actual reservoir. The reservoir performance was determined to be sensitive to the inflow data. The results indicate that climatic change has potentially important implications for the operation of the example reservoir system.     

Effects of feeding strategies on the performance of an anaerobic discontinuous reactor containing immobilized biomass with circulation system for liquid-phase mixing.

Data on the influence of feeding strategy on the performance of a fed-batch anaerobic sequencing reactor containing biomass immobilized on polyurethane foam and subjected to liquid phase circulation are presented and discussed. Six-hour cycles, temperature of 30 degrees C and circulation flow rate of 6 L/h were used. During each cycle 890 mL of synthetic domestic wastewater, with organic matter concentration of 500 mgCOD/L were fed to the reactor. The feeding strategies were implemented using fill times of 6 min (batch mode), 60, 120, 240 (fed-batch/batch mode) and 360 min (fed-batch mode). The system attained high efficiency and stability for all the operating conditions, and the substrate removal efficiency based on filtered samples presented a slight decrease from 85% to 81% when fill time was increased from 6 min to 360 min. A model considering a first-order kinetic equation was fitted to the experimental data. The apparent kinetic parameters for both batch and fed-batch phases were estimated, thus permitting evaluation of the influence of the feeding strategy on the reactor performance. The current system may be considered flexible in terms of the operating conditions it is subjected to.     

An alternative approach to the operation of multinational reservoir systems: Application to the Amistad &; Falcon system (Lower Rio Grande/Río Bravo)

An optimization approach for the operation of international multi-reservoir systems is presented. The approach uses Stochastic Dynamic Programming (SDP) algorithms – both steady-state and real-time – to develop two models. In the first model, the reservoirs and flows of the system are aggregated to yield an equivalent reservoir, and the obtained operating policies are disaggregated using a non-linear optimization procedure for each reservoir and for each nation's water balance. In the second model a multi-reservoir approach is applied, disaggregating the releases for each country's water share in each reservoir. The non-linear disaggregation algorithm uses SDP-derived operating policies as boundary conditions for a local time-step optimization. Finally, the performance of the different approaches and methods is compared. These models are applied to the Amistad-Falcon International Reservoir System as part of a binational dynamic modeling effort to develop a decision support system tool for a better management of the water resources in the Lower Rio Grande Basin, currently enduring a severe drought.     

Analysis and Modelling of Stormwater Volume Control Performance of Rainwater Harvesting Systems in Four Climatic Zones of China

Rainwater harvesting has been widely used to alleviate urban water scarcity and waterlogging problems. In this study, a water balance model is developed to continuously simulate the long-term (57 to 65 years) stormwater capture efficiency of rainwater harvesting systems for three water demand scenarios at four cities across four climatic zones of China. The impacts of the “yield after spillage” (YAS) and “yield before spillage” (YBS) operating algorithms, climatic conditions, and storage and demand fractions on stormwater capture efficiency of rainwater harvesting systems are analyzed. The YAS algorithm, compared with the YBS, results in more conservative estimations of stormwater capture efficiency of rainwater harvesting systems with relatively small storage tanks (e.g., ≤50 m³). The difference between stormwater capture efficiency calculated using the YBS and YAS algorithms can be remedied by increasing storage capacity and reduced by decreasing water demand rates. Higher stormwater capture efficiency can be achieved for rainwater harvesting systems with higher storage and demand fractions and located in regions with less rainfall. However, the lager variations in annual rainfall in arid zones may lead to unstable stormwater management performance of rainwater harvesting systems. The impacts of storage and demand fractions on stormwater capture efficiency of rainwater harvesting systems are interactive and dependent on climatic conditions. Based on the relationships among storage capacity, contributing area, water demand, and stormwater capture efficiency of rainwater harvesting systems, easy-to-use equations are proposed for the hydrologic design of rainwater harvesting systems to meet specific stormwater control requirements at the four cities.