采用动网格与滑移网格技术的垂直轴风力机启动性能计算

针对垂直轴风力机的启动问题,采用动网格和滑移网格技术进行数值模拟和比较分析,并与公开发表文献的风洞实验数据进行了对比验证。文章通过对风力机启动的非定常过程进行研究,获得了风力机启动性能,并分析了计算所得的速度场。通过分析和综合对比显示,被动型动网格更适于风力机的启动性能模拟,得到的速度场与文献研究结果更接近。该模拟方法更符合流场的实际状态,为垂直轴风力机启动性能数值模拟提供了新思路。     

基于风洞实验的风力机叶片气动负载计算方法

提出一种基于风洞实验的风力机叶片气动负载计算方法。理论分析Beddoes-Leishman空间状态模型的非定常气动力特性,结合风洞实验数据和Beddoes-Leishman模型开发动态气动负载的数值计算程序。利用开发程序,分别详细计算DU97W300-10翼型在不同攻角区间,即线性区、失速区和全区的非定常气动系数,分析每个区间内附着流和分离流对翼型动态气动特性的影响。结果表明,在所有攻角区域的气动参数计算结果均能很好地与理论分析结果达成一致,翼型风洞实验可有效保证特定翼型动态气动负载计算的准确性。     

基于RTD曲线优化八流中间包控流装置的研究

控流装置对钢液流动特性的影响较大,采用物理模拟结合数值模拟的方法对某钢厂八流中间包进行了挡墙优化,分析了不同挡墙方案中间包的RTD曲线并进行相关计算,根据计算结果选取较优方案。水模型实验和数值模拟结果表明,原型中间包加入控流装置后流场趋于合理,钢液的停留时间比较一致。其中,V-2方案的死区体积分数小,各流一致性好,有利于均匀钢液的成分和温度,促进夹杂物上浮,综合效果好。     

增压板迎风角对浓缩风能装置流场特性的影响

为提高浓缩风能型风电机组的输出功率,以增压圆弧板及其迎风角为研究对象,对浓缩风能装置内部流场进行仿真分析,并通过车载实验和风洞实验数据验证数值模拟结果的可靠性。结果表明,增压圆弧板可有效提高浓缩风能效率;综合考虑制造成本、流场特性和风切变等因素,增压板迎风角为60°的浓缩风能装置模型流场特性较佳,最大流速是来流风速的2.36倍。     

双圆弧叶型压气机叶栅气动特性的实验研究

对双圆弧叶型（DCA）压气机叶栅在低速大尺寸风洞上进行了实验研究，利用五孔束状探针对栅前、流道里和出口流场进行了详细的测量以及流场显示。实验结果表明,DCA叶栅出口近两端壁的通道涡和端壁／吸力面角区分离泡的存在，造成叶栅两端区较高的二次流损失。与CDA相比，DCA尾缘流动较差；与NACA65相比，DCA的负荷沿叶高分布不均匀。     

折流板换热器壳程流场数值模拟与结构优化

基于多孔介质与分布阻力的概念,采用FLUENT软件对单弓形折流板换热器的壳侧流场进行了三维数值模拟,模拟结果与实验结果吻合较好。在此基础上针对折流板换热器壳程压降大、能耗高,存在传热死区等的缺点,提出了壳程流场的改进方案,通过数值模拟可以看到壳程流场改进后不仅具有压降低、场协同性能好、基本无传热死区等特点,而且在一定程度上还提高了管束抗流体诱导振动的性能。     

螺旋隔板光滑管单管换热器的数值模拟

采用FLUENT6.0软件对整个螺旋隔板光滑管单管换热器的流场、温度场和压力场进行数值模拟,并与实验测量和计算结果进行了对比,验证了数值模拟的准确性。流场模拟结果显示,流体在壳程呈螺旋状流动,没有死区,而且流速比较均匀,变化比较小,从而进一步验证了许多学者经过实验研究分析得出的螺旋隔板换热器具有的优良性能。     

汽轮机末级模化叶栅的静态实验研究及其槽道内流场的数值分析

在低速环形叶栅风洞中，对国产３００ＭＷ汽轮机低压末级静叶的模化叶栅进行了实验研究。用全三元欧拉计算程序数值模拟了模化叶栅的流场。通过两个不同方案的吹风实验和数值计算，讨论了在实际工程应用中弯扭叶片对改善流场的作用。图６参９     

气体横掠单管强制对流换热的大涡模拟

应用大涡模拟与二价全展开ETC有限元离散格式相结合的方法对气体横掠单管强制对流换热进行了数值模拟,分别计算了气体横掠团管和方管时的温度场,得到了管壁平均换热系数,数值结果与实验关联式符合较好。同时还表明大涡模拟方法善于捕捉温度场以及流场涡系的时间演化过程,非常适合于具有大尺度涡的绕流运动温度场的分析。     

电站凝汽器水侧流场均匀性的定量分析

尝试了一种定量计算凝汽器管程流场均匀性的方法:采用多孔介质模型及数值模拟方法对凝汽器水室流场进行数值分析;然后采用速度相对标准偏差对凝汽器管程的流场分布进行定量计算,将上述方法在某双流程凝汽器水侧流动的分析上进行了应用,结果表明管程流场均匀性定量分析方法可以对凝汽器管程流场的均匀性进行定量计算;文章所分析的双流程凝汽器第一流程的均匀性差于第二流程。     

A natural ventilation wind tower with heat pipe heat recovery for cold climates

Commercial wind towers are passive ventilation technology based on traditional wind towers of the Middle East. Typical operation of wind towers in cold – mild climates is generally limited to summer-seasons as the outdoor air is too cold to be introduced into spaces for the majority of the year. In addition, the use of natural ventilation solutions has been seen to increase heat loss in buildings and lead to increased energy cost. Wind towers are normally shut down for the sake of avoiding indoor heating energy losses during winter months. Consequently, the concentration of pollutants has seen to rise above the guideline levels, which can lead to ill health. To improve the year-round capabilities of wind towers, a heat recovery system utilising the combination of heat pipes and heat sink was incorporated into a multi-directional wind tower. This study investigates the potential of this concept through the use of numerical analysis and wind tunnel experiments for validation. The findings showed that the wind tower with heat pipes was capable of meeting the required ventilation rates above an inlet air velocity of 1 m/s. In addition to sufficient ventilation, the integration of heat pipes had a positive effect on thermal performance of the wind tower; it raised the supply air by up to 4.5 K. The technology presented here is subject to a patent application (PCT/GB2014/052263).     

地铁双线隧道内流动特性的数值模拟

列车运行时的活塞效应对隧道内空气的流动特性有显著的影响。采用CFD数值模拟的方法,着重对地铁双向隧道内列车运动对隧道内空气流动特性的影响作了初步的讨论。模拟结果显示,在双线隧道中,流场的分布是两列车所引起的活塞效应共同作用的结果;两列车相向行驶时,各自的活塞效应会减弱甚至相互抵消,不利于区间隧道内的自然通风。     

Two-sided wind catcher performance evaluation using experimental,numerical and analytical modeling

Experimental wind tunnel and smoke visualization testing as well as CFD and analytical modeling were conducted to investigate the performance of a two-sided wind catcher. This type of wind catcher is divided internally into two halves for the purposes of air supply and extract. In this study, the two-sided wind catcher model was constructed of two similar one-sided wind catcher models, which were attached together back to back. These one-sided models are 1:40 scale models of Kharmani's School wind catcher in the city of Yazd. Experimental investigations were carried out using an open-circuit wind tunnel and both the induced volumetric airflow into the building and the pressure coefficients around all surfaces of the wind catcher model were measured at various wind angles. Furthermore, the CFD simulation was also used to evaluate the pressure coefficient distribution and airflow pattern around and through the wind catcher. Additional experimental tests and computational fluid dynamics simulation of the wind catcher in the wind tunnel were also conducted in order to assess the accuracy of measurement procedures and the uncertainty of experimental results. This article also represents a semi-empirical approach in which experimental data were used for a detailed analytic model, in order to provide an accurate estimate of the performance of wind catchers. It was found that for an isolated two-sided wind catcher model, the maximum efficiency is achieved at the angle of 90°. At this air incident angle the wind catcher efficiency increases approximately 20% more than the one at zero angle. The experimental investigations demonstrated the potential of two-sided wind catcher for enhancing the natural ventilation inside buildings. It can be seen that CFD simulation and analytical modeling results have a good agreement with the experimental results. Theoretical modeling can also help to assess the accuracy of measurement procedures and the uncertainty of experimental results.     

Performance evaluation of passive cooling in office buildings based on uncertainty and sensitivity analysis

Natural night ventilation is an interesting passive cooling method in moderate climates. Driven by wind and stack generated pressures, it cools down the exposed building structure at night, in which the heat of the previous day is accumulated. The performance of natural night ventilation highly depends on the external weather conditions and especially on the outdoor temperature. An increase of this outdoor temperature is noticed over the last century and the IPCC predicts an additional rise to the end of this century. A methodology is needed to evaluate the reliable operation of the indoor climate of buildings in case of warmer and uncertain summer conditions. The uncertainty on the climate and on other design data can be very important in the decision process of a building project.The aim of this research is to develop a methodology to predict the performance of natural night ventilation using building energy simulation taking into account the uncertainties in the input. The performance evaluation of natural night ventilation is based on uncertainty and sensitivity analysis.The results of the uncertainty analysis showed that thermal comfort in a single office cooled with single-sided night ventilation had the largest uncertainty. The uncertainties on thermal comfort in case of passive stack and cross ventilation were substantially smaller. However, since wind, as the main driving force for cross ventilation, is highly variable, the cross ventilation strategy required larger louvre areas than the stack ventilation strategy to achieve a similar performance. The differences in uncertainty between the orientations were small.Sensitivity analysis was used to determine the most dominant set of input parameters causing the uncertainty on thermal comfort. The internal heat gains, solar heat gain coefficient of the sunblinds, internal convective heat transfer coefficient, thermophysical properties related to thermal mass, set-point temperatures controlling the natural night ventilation, the discharge coefficient C_d of the night ventilation opening and the wind pressure coefficients C_p were identified to have the largest impact on the uncertainty of thermal comfort.The impact of the warming climate on the uncertainty of thermal comfort was determined. The uncertainty on thermal comfort appeared to increase significantly when a weather data set with recurrence time of 10 years (warm weather) was applied in the transient simulations in stead of a standard weather data set. Natural night ventilation, designed for normal weather conditions, was clearly not able to ensure a high probability of good thermal comfort in warm weather. To ensure a high probability of good thermal comfort and to reduce the performance uncertainty in a warming climate, natural night ventilation has to be combined with additional measures. Different measures were analysed, based on the results of the sensitivity analysis. All the measures were shown to significantly decrease the uncertainty of thermal comfort in warm weather. The study showed the importance to carry out simulations with a warm weather data set together with the analysis under typical conditions. This approach allows to gain a better understanding of the performance of a natural night ventilation design, and to optimize the design to a robust solution.     

Evaluation of pressure coefficients and estimation of air flow rates in buildings employing wind towers

Wind pressure coefficients at various openings of a wind tower were determined by testing a scale model of the building in a boundary layer wind tunnel. Wind towers (or Baud-Geers) are structures which have been employed in Iran and neighbouring countries for natural ventilation and passive cooling. Tests were conducted on an isolated tower, the tower and adjoining house, and the tower and house surrounded by a courtyard. The wind pressure coefficients at the tower and house openings were determined at various wind angles for two types of terrain: suburban and open country. The air flow rates were then estimated from a knowledge of the wind pressure coefficients at the building apertures. It was concluded that the presence of a courtyard around the structure and the angle of incidence of the wind influence the rate and the direction of air flowing from the tower to the house. If leeward openings of the tower can be closed (for example, by automatic dampers) restricting the air leaving these apertures, the air flow rate from the tower to the house can be greatly increased. The results of this investigation are believed to provide assistance to architects and engineers in the design of wind towers for desired ventilation rates in buildings.     

Application of ANN to explore the potential use of natural ventilation in buildings in Turkey

Indoor natural ventilation provides both the circulation of clear air and the decrease of indoor temperature, especially, during hot summer days. In addition to openings, building dimensions and position play a significant role to obtain a uniform indoor air velocity distribution. In this study, the potential use of natural ventilation as a passive cooling system in new building designs in Kayseri, a midsize city in Turkey, was investigated. First, indoor air velocity distributions with respect to changing wind direction, magnitude and door openings were simulated by the FLUENT package program, which employs finite element methods. Using the simulated data an artificial neural network (ANN) model was developed to predict indoor average and maximum air velocities. The simulations produced by FLUENT show that the average indoor air velocity is generally below 1.0 m/s for the local prevailing wind directions. The simulations results suggest that, in addition to the orientation of buildings in accordance with prevailing wind directions, a proper indoor design of buildings in the area can significantly increase the capability of air ventilation during warm summer days. It was found that a high correlation exists between the simulated and the ANN predicted data indicating a successful learning by the proposed ANN model. Overall, the evaluation of the network results indicated that the ANN approach can be utilized as an efficient tool for learning, training and predicting indoor air velocity distributions for natural ventilation.     

NUMECA软件在超临界汽轮机调节级导叶栅流场的数值校核

采用商用软件NUMECA数值模拟了大尺度扇形叶栅内的流动状况.通过将计算结果与低速风洞实验研究测量得到的超临界汽轮机调节级导叶原型叶栅的试验数据进行对比研究,认为应用NUMECA商用软件计算叶栅绕流既能够定性地又能近似定量地反映实际流动状况.     

来流马赫数对叶栅吸力面可压边界层稳定性影响研究

针对叶栅高速流动稳定性预测及转捩问题，采用理论分析与实验测量相接合的方法。首先推导出正交曲线坐标系下三维扰动波的抛物化稳定性方程（PSE），在风洞实验中，采用叶栅表面压力测孔测量了设计叶栅表面静压分布。根据表面静压分布测量值，通过求解Falkner—Skan方程以获得不同来流马赫数下边界层内速度、压力、密度等参数的分布。将以上结果作为边界层平均流动值，结合数值离散化的正交曲线坐标系非线性抛物化稳定性方程（PSE）对流动的稳定性进行特征值分析。数值离散采用六阶精度差分格式，采用大步长隐格式法求解方程以保证求解的稳定性。计算结果表明本文所选用的实验叶栅由于加工量较小并采用后部加载叶型设计，边界层流动相对稳定。来流马赫数增加对边界层稳定性有微弱影响，会导致流动趋于不稳定。     

Using CFD to investigate ventilation characteristics of vaults as wind-inducing devices in buildings

This paper investigates the potential of the vaulted roofs for improving wind-induced natural ventilation, using computational fluid dynamics (CFD) three-dimensional modelling. This has been carried out in a parametric study considering different climatic and geometrical parameters. Using Fluent 5.5 program, natural ventilation performance has been modelled and assessed according to the value of airflow rate, and the quality of internal airflow distribution. It has been concluded that utilisation of vaulted roofs for natural ventilation increases inflow rate of the building, and re-distribute internal airflow currents by attracting some of the air to leave through roof openings instead of walls openings. This has improved ventilation conditions in the upstream and central zones of the building, but not in the downstream zone. Natural ventilation performance of two equivalent domed and vaulted roofs has also been compared. Results showed that there are many similarities between domed and vaulted roofs in terms of their natural ventilation performance. The advantage of any roof shape in air suction is highly dependant on wind direction.     

高地温隧洞围岩温度场有限元分析

针对高地温隧洞存在的严重高温现象,以齐热哈塔尔水电工程为例,采用ANSYS软件对隧洞围岩高温段自然通风和采取降温措施两种工况进行模拟研究。与实测数据对比分析表明,随着自然通风和降温措施时间的增加,隧洞内部温度逐渐降低,最后达到平衡状态,模拟结果与实测数据基本吻合;同时对于隧洞整体围岩降温周期长、难度大的特点,可采取局部降温的措施达到施工作业要求的温度,这为工程项目的实施提供了可靠参考。