Numerical investigations on dynamic stall of low Reynolds number flow around oscillating airfoils

This paper presents a 2D computational investigation on the dynamic stall phenomenon associated with unsteady flow around the NACA0012 airfoil at low Reynolds number (Re_c ≈ 10⁵). Two sets of oscillating patterns with different frequencies, mean oscillating angles and amplitudes are numerically simulated using Computational Fluid Dynamics (CFD), and the results obtained are validated against the corresponding published experimental data. It is concluded that the CFD prediction captures well the vortex-shedding predominated flow structure which is experimentally obtained and the results quantitatively agree well with the experimental data, except when the blade is at a very high angle of attack.     

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.     

有限推力登月飞行器燃料消耗研究

首先介绍了使用基于双二体问题的圆锥曲线拼合法和齐奥尔科夫斯基公式进行登月飞行器燃料消耗量的计算方法;接着导出了地月固联三体坐标系中最优轨道情况下登月飞行器燃料消耗量的计算方法;最后给出了在一定推力范围内不同比冲常规发动机分别使用上述第1种方法得到的燃料消耗和使用上述第2种方法得到的发动机工作时间和燃料消耗的仿真结果。结果表明两种方法得到的结论吻合得很好。     

Proof of Concept MFD Optimization of the Aftbody Geometry of Axisymmetric Slender Body Based on Wave Drag Considerations

A comprehensive, universally valid, elegant and yet simple method to design slender axisymmetric body of minimum wave drag in transonic and supersonic flows is developed. Computational aerodynamics is also used as a tool for numerical experiments in gaining physical understanding of the drag mechanism due to the geometry of the aftbody, such as the correlation between wave drag and wave distribution of the aftbody geometry. The method utilizes MFD （modified feasible direction） based optimization program, along with the linear slender body aerodynamics, for its elegance and generic optimization convenience. The efforts are focused on inviscid flow. A practical method of reducing the wave drag of a given body is developed for both bodies with pointed end and with base area, using shock wave generator at a particular location on the aftbody. The results show that the MFD optimization program can be effectively utilized in an aerodynamic optimization problem.     

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.     

Study of Passive Deck-Flaps Flutter Control System on Full Bridge Model. I: Theory

A passive aerodynamic control method for suppression of the wind-induced instabilities of a very long span bridge is presented in this paper. The control system consists of additional control flaps attached to the edges of the bridge deck. Control flap rotations are governed by prestressed springs and additional cables spanned between the control flaps and an auxiliary transverse beam supported by the main cables of the bridge. The rotational movement of the flaps is used to modify the aerodynamic forces acting on the deck and provides aerodynamic forces on the flaps used to stabilize the bridge. A time-domain formulation of self-excited forces for the whole three-dimensional suspension bridge model is obtained through a rational function approximation of the generalized Theodorsen function and implemented in the FEM formulation. This paper lays the theoretical groundwork for the one that follows.     

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.     

Influence of some factors on the aerodynamic behavior of long-span suspension bridges

As the span length of suspension bridges increases, the diameter of cables and thus the wind load acting on them, the nonlinear wind-structure interaction and the spatial non-uniformity of wind speed (including the vertical and horizontal variations) all increase consequently, which may have unnegligible influence on the aerostatic and aerodynamic behavior of long-span suspension bridges. In this paper, the models of aerostatic and aerodynamic forces are established, in which the nonlinear wind-structure interaction and the spatial non-uniformity of wind speed are both considered. By taking the Runyang Bridge over the Yangtze River as example, effects of the nonlinear wind-structure interaction, wind speed spatial non-uniformity, and the cable's wind load on the aerostatic and aerodynamic behavior of the bridge are investigated analytically. The results show that the aerostatic behavior is significantly influenced by these factors, but for the aerodynamic stability, it is greatly influenced by the nonlinear wind-structure interaction and the horizontal variation of wind speed, and the other factors have no influence on it.     

Analysis of flow in rotating packed beds via CFD simulations—Dry pressure drop and gas flow maldistribution

Three-dimensional unsteady-state turbulent rotating single-phase flows were simulated in rotating packed beds (RPB) and were validated using overall dry pressure drop measurements for three RPB designs [Liu, H.-S., Lin, C.-C., Wu, S.-C., Hsu, H.-W., 1996. Characteristics of a rotating packed bed. Industrial and Engineering Chemistry Research 35, 3590-3596; Sandilya, P., Rao, D.P., Sharma, A., Biswas, G., 2001b. Gas-phase mass transfer in a centrifugal contactor. Industrial and Engineering Chemistry Research 40, 384-392; Zheng, C., Guo, K., Feng, Y.D., Yung, C., 2000. Pressure drop of centripetal gas flow through rotating bed. Industrial and Engineering Chemistry Research 39, 829-834]. Analysis of the radial and tangential velocities highlighted the impact of gas feed entrance effects on the peripheral gas maldistribution in the rotating packing module. Recommendations were formulated for an optimum design with the aim to reduce gas flow maldistribution in RPBs. Breakdown of the overall pressure drop in its modular components for the housing, the rotating packing module, the free inner rotational zone, and the gas disengagement showed that the dissipation in the rotating packing could be a minor contributor to the overall pressure drop which may be undesirable in terms of RPB mass transfer and reaction efficiencies. Analysis of the simulated pressure drops allowed development of CFD-based Ergun-type semi-empirical relationships in which the gas-slip and radial acceleration effects, the laminar and inertial drag effects, and the centrifugal effect were aggregated additively to recompose the pressure drops in the rotating packing module.