冷却塔内气流流场特性研究及应用

冷却塔是火力发电厂循环水系统的重要设备,冷却塔的冷却效率对机组的微增功率有着比较重要的影响,冷却效率的提高有助于节约发电能耗。冷却塔的效率与其空气动力特性有着紧密的联系,本文以华电集团江苏分公司望亭发电有限公司3号机冷却塔的节能改造为例,研究了冷却塔内气流流场的特性,并阐述了针对该特性采取的技术措施在冷却塔优化改造中的应用实践。     

Performances of ideal wind turbine

If there is an ideal wind turbine, its performances will be the pursuit goals for designing the actual wind turbine. In this paper, the wind turbine that has the maximum efficiency is defined as ideal wind turbine, which has three main features: lift-drag ratio is infinite, it has enough number blades so that the blade tip and root losses can be ignored, and its blades are limited in width. Using blade element theory, the differential equations of power, torque, lift and thrust of blade element were derived, and the expressions of power, torque, lift and thrust coefficients of the ideal wind turbine were gained by integrating along the blade span. Research shows that the power, torque and lift coefficients of the ideal wind turbine are functions of tip-speed ratio. When the lift-drag ratio and the tip-speed ratio is approaching infinity, power coefficient of the ideal wind turbine is close to the Betz limit; The torque limit is 0.401 when the tip-speed ratio equals about 0.635; The Lift limit is 0.578 when the tip-speed ratio equals about 0.714; The thrust coefficient is 8/9, which is unrelated with tip-speed ratio. For any wind turbine which tip-speed ratio is less than 10, the power coefficient is unlikely to exceed 0.585, for any high-speed wind turbine which tip-speed ratio is greater than 6, the torque coefficient in steady state is unlikely to exceed 0.1, and the lift coefficient is unlikely to exceed 0.2.     

Innovative improvement of a drag wind turbine performance

Drag type wind turbines have strong potential in small and medium power applications due to their simple design. However, a major disadvantage of this design is the noticeable low conversion efficiency. Therefore, more research is required to improve the efficiency of this design. The present work introduces a novel design of a three-rotor Savonius turbine with rotors arranged in a triangular pattern. The performance of the new design is assessed by computational modeling of the flow around the three rotors. The 2D computational model is firstly applied to investigate the performance of a single rotor design to validate the model by comparison with experimental measurements. The model introduced an acceptable accuracy compared to the experimental measurements. The performance of the new design is then investigated using the same model. The results indicated that the new design performance has higher power coefficient compared with single rotor design. The peak power coefficient of the three rotor turbine is 44% higher than that of the single rotor design (relative increase). The improved performance is attributed to the favorable interaction between the rotors which accelerates the flow approaching the downstream rotors and generates higher turning moment in the direction of rotation of each rotor.     

Triaxial Load Testing of Metal and FRP Roof-to-Wall Connectors

The allowable capacity of conventional roof-to-wall metal connectors is based on results of unidirectional component tests that do not simulate triaxial aerodynamic loading effects induced by high-wind events. The results of wind and wind-driven rain tests conducted at a full-scale facility were used to create a database on aerodynamic and aerohydrodynamic load effects on roof-to-wall connectors. Based on these results, three axial mean force components (triaxial mean loads) were combined into a series of resultant mean force vectors. A new test protocol was then developed for roof-to-wall connectors under simulated triaxial loading as opposed to simple uniaxial loading. The findings confirm that current testing methods tend to overestimate the actual load capacities of metal connectors. The performance of a nonintrusive roof-to-wall connector system using fiber-reinforced polymer (FRP) ties was also tested and compared with that of a traditional metal connector under simulated aerodynamic loads. The test results demonstrated the validity of FRP ties as an alternative to hurricane clips for use in timber roof-to-wall connection systems.     

Improvement of the Parameterized Identification Model Using Quasi-Steady and Nonuniform Inflow Aerodynamic Model

Compared with those of a fixed-wing aircraft, the dynamics of a rotorcraft are significantly more complex. One of the major challenges in the design of an autonomous helicopter is the development of a flight dynamic model, which can be useful for simulation studies and for the design of control law and navigational aspects. There is always a trade-off from the accuracy of the mathematical model to the more simplified model required for a control design as far as the helicopter rotor/fuselage dynamics is concerned. Small-scale helicopters posses a higher bandwidth of dynamics; hence, models developed from the first principle alone do not fulfill the needs, and more-sophisticated mathematical models are thus required. The main objective of the present work is to improve the parameterized identification model by replacing it with a most-general flight dynamic model for a minihelicopter. This model includes the rotor blade flap dynamics, stabilizer bar dynamics, and vehicle dynamics, which will be applicable for a general maneuvering flight. A systematic study is undertaken to analyze the influence of inflow models and flap response on the helicopter trim. Stability of the minihelicopter is also analyzed; except for phugoid, all other modes are stable in hover and high forward flight conditions.     

Aerodynamic Part Feeding: Development of Aerodynamic Orienting Devices

Because of the pressure for continuous rationalisation, companies especially in industrialised countries, have to reduce their unit costs. A common way to fulfil this demand is to reduce labour costs by using fully automatic assembly systems. The assembly process itself has been optimised using many disciplines. Assembly has become more flexible and faster. This rapid improvement, however, cannot be observed in the area of part-feeding systems. In spite of the fact that part feeding is a key technology for high efficiency in fully automated assembly systems, the devices which provide the assembly processes with small parts have not generally improved in the last decades. Hence, innovative feeding technologies based on aerodynamic effects are being developed at the Institute of Production Systems. In this paper we focus on the orientation function of the feeding process.     

导弹气动数据库管理系统分析与设计

导弹气动数据库管理系统结合具体风洞试验类型,建立相关数据结构.该系统由管理平台、后置处理、前置处理及其他软件接口部分组成.系统关键技术含气动数据结构的设计、数据的标准化表示、数据的对比分析及模型数据的前置处理.     

The inverse design of the wind turbine blade sections by the singularities method

The aerodynamic characteristics of wind turbines are closely related to the geometry of their blades. The innovation and the technological development of wind turbine blades can be centred on two tendencies. The first is to improve the shape of existing blades; the second is to design new shapes of blades. The aspiration in the two cases is to achieve an optimal circulation and hence enhancing some more ambitious aerodynamic characteristics. This paper presents an inverse design procedure, which can be adapted to both thin and thick wind turbine blade sections aiming to optimise the geometry for a prescribed distribution of bound vortices. A method for simulating the initial contour of the blade section is exposed, which simultaneously satisfy the aerodynamic and geometrical constraints under nominal conditions. A detailed definition of the function characterising the bound vortex distribution is presented. The inviscid velocity field and potential function distributions are obtained by the singularities method. In the design method implemented, these distributions and the circulation of bound vortices on the camber line of the blade profile, are used to rectify its camber in an iterative calculation leading to the final and optimal form of the blade section once convergence is attained. The scheme proposed has been used to design the entire blade of the wind turbine for a given span-wise distribution of bound circulation around the blade contour.     

A wind turbine blade profile analysis code based on the singularities method

The aerodynamic characteristics of wind turbines are closely related to the geometry of their blade profiles. The innovation and the technological development of wind turbine blade profiles can be centred on two tendencies. The first is to improve the shape of the existing airfoils and the second is to design new shapes of airfoils in order to get some more ambitious aerodynamic characteristics and enhanced performance.The aim of this paper is to develop an accurate airfoil analysis lower order code, based on the singularities method, for wind turbine applications. The 2D incompressible potential flow model has been used. In the implementation of the singularities method, source–vortex distributions over the airfoil contour are used to compute the flow characteristics. The accuracy and the validity of the results have been tested using experimental data obtained from Wind Turbine Airfoil Catalogue “Risø National Laboratory, Roskilde, Denmark, August 2001” and have shown considerable agreement.     

空气动力学在F1赛车上的运用

在F1赛车的研究中,空气动力学研究的核心目的是在保证赛车获得足够压力的情况下拥有最小的空气阻力,以提高赛车的速度和高速行驶的稳定性。在空气动力学实验中,工程师们最关注的主要是3个方面的内容:下压力、阻力和灵敏性(敏感度)。巨大的下压力可以提高赛车的过弯极限,但是在理想状态下,下压力的增加不应当带来赛车阻力的增加,但是不可避免的却会牺牲赛车的部分极速。赛车的空气动力学灵敏性(敏感度)则是指赛车的状态性能对于空气动力学环境改变时自身变化的强弱,例如由不平整的赛道路面带来的赛车翼片以及底盘和路面距离之间的频繁变化时,赛车性能所受到的干预强弱。