Xiaojing Sun

Numerical study on coupling effects among multiple Savonius turbines

A Savonius rotor can be used as a wind or water current energy conversion device that produces electricity. In spite of their simple structure and assembly, Savonius turbines have less commercial appeal than other types of turbines due to their relatively low energy conversion efficiency. In order to increase the output power of a Savonius turbine, most studies have only focused on optimization of the rotor configuration or installation of ancillary equipment around the rotor. However, previous research has found that a beneficial interaction that existed between two parallel Savonius turbines can also augment the power output of each rotor if they are rotating side by side. This paper numerically examines the interactions among multiple Savonius turbines with the help of the commercial computational fluid dynamics software fluent and finds that these coupling effects can effectively increase the overall power output of a Savonius turbine farm, especially when Savonius turbines are arranged relatively clo...

A three-dimensional numerical study of the Magnus wind turbine with different blade shapes

Although the Magnus type wind turbine has many benefits over conventional blade-type wind turbines, it normally has low wind energy utilization efficiency. Therefore, it is important to seek effective ways of improving the Magnus wind turbine power performance in order to promote its application. As blade aspect ratio is a critical parameter influencing the Magnus wind turbine performance, a 3D numerical study of a Magnus type wind turbine which is equipped with cylindrical blades with different aspect ratios has been conducted in this paper. In addition, various cylinder shapes, including truncated cone and wavy cylinder, have also been used and their effects on the performance of the Magnus wind turbine are analyzed. Performance characteristics such as power, torque, and thrust coefficients of the Magnus turbine with different blade shapes are compared and discussed with the aim of identifying the desirable blade characteristics for this type of turbine.

Aerodynamic performance and characteristic of vortex structures for Darrieus wind turbine. I. Numerical method and aerodynamic performance

A recently developed in-house computational fluid dynamics (CFD) code is used to simulate an H-Darrieus wind turbine. Aerodynamic performance of the simulated Darrieus turbine having different number of blades and turbine solidity is analyzed and compared for different tip speed ratios. As expected, the power coefficient of the simulated Darrieus turbine increases with the increase of tip speed ratio until a maximum is reached. However, the power coefficient then decreases with further increases in the tip speed ratio. The calculated power curve is in good agreement with experimental results. The results obtained suggest that this developed CFD code can accurately predict the aerodynamic characteristics of an H-Darrieus turbine. In addition, it is found that the solidity has considerable influence on the power coefficient of the simulated turbine in the present work. The smaller the solidity, the higher will be the optimal tip speed ratio and the wider will be the range of tip speed ratios at which the H-...

Research on energy extraction characteristics of an adaptive deformation oscillating-wing

Oscillating foil machines represent a type of flow energy harvesters which perform pitching and plunging motions simultaneously to harness the energy from incoming stream. In this paper, a new adaptive deformation oscillating wing was proposed and the theoretical performance of such a concept was studied here through unsteady two-dimensional simulations using an in-house developed computational fluid dynamics code. During operation, the proposed oscillating foil whose initial shape is symmetric can be deformed into a cambered foil, which aims to produce large lift force. Our numerical results suggest that the power efficiency of the proposed oscillating foil can be about 16.1% higher than the conventional oscillating foil without deformation. In addition, the effects of the maximum bending displacement and effective angle of attack on the efficiency of proposed oscillating foil were also discussed in this work.

Numerical study on aerodynamic performances of the wind turbine rotor with leading-edge rotation

The flow control using leading-edge rotating cylinder on both two-dimensional NACA 63418 airfoil section and three-dimensional two-bladed wind turbine rotor has been studied by means of numerical simulations. For the two-dimensional NACA 63418 airfoil with a fasting spinning cylinder at the leading-edge, flow separation occurs on the pressure side of the airfoil near the clearance between rotating cylinder and stationary airfoil at small angles of attack; however, flow separation on the suction side of the airfoil can be suppressed at large angles of attack. The aerodynamic performances of the leading-edge rotation (LER) wind turbine rotors with two twisted/non-tapered blades and with two twisted/tapered blades have been studied, respectively. The result shows that the power efficiency of the LER wind turbine with twisted/non-tapered blades is superior to the uncontrolled wind turbine rotor remarkably at high tip speed ratios. The aerodynamic control effects of the leading-edge rotating cylinder have also...

Research on the aerodynamic characteristics of a lift drag hybrid vertical axis wind turbine

Compared with a drag-type vertical axis wind turbines, one of the greatest advantages for a lift-type vertical axis wind turbines is its higher power coefficient (Cp). However, the lift-type vertical axis wind turbines is not a self-starting turbine as its starting torque is very low. In order to combine the advantage of both the drag-type and the lift-type vertical axis wind turbines, a lift drag hybrid vertical axis wind turbines was designed in this article and its aerodynamics and starting performance was studied in detail with the aid of computational fluid dynamics simulations. Numerical results indicate that the power coefficient of this lift drag hybrid vertical axis wind turbines declines when the distance between its drag-type blades and the center of rotation of the turbine rotor increases, whereas its starting torque can be significantly improved. Studies also show that unlike the lift-type vertical axis wind turbines, this lift drag hybrid-type vertical axis wind turbines could be able to solve the problem of low start-up torque. However, the installation position of the drag blade is very important. If the drag blade is mounted very close to the spindle, the starting torque of the lift drag hybrid-type vertical axis wind turbines may not be improved at all. In addition, it has been found that the power coefficient of the studied vertical axis wind turbines is not as good as expected and possible reasons have been provided in this article after the pressure distribution along the surfaces of the airfoil-shaped blades of the hybrid turbine was analyzed.

The effect of variations in first- and second-order derivatives on airfoil aerodynamic performance

ABSTRACT The geometric factors which influence airfoil aerodynamic performance are attributed to variations in local first- and second-order curvature derivatives. Based on a self-developed computational fluid dynamics (CFD) program called UCFD, the influence of local profile variations on airfoil aerodynamic performance in different pressure areas is investigated. The results show that variations in first- and second-order derivatives of the airfoil profiles can cause fluctuations in airfoil aerodynamic performance. The greater the variation in local first- and second-order derivatives, the greater the fluctuation amplitude of the airfoil aerodynamic coefficients. Moreover, at the area near the leading edge and the shock-wave position, the surface pressure is more sensitive to changes in first- and second-order derivatives. These results provide a reference for airfoil aerodynamic shape design.

Fluid–structure interaction analysis of a high-pressure regulating valve of a 600-MW ultra-supercritical steam turbine

A high-pressure regulating valve is one of the most critical components in ultra-supercritical steam power plants and constantly works under the condition of high temperature and high pressure. In order to control the flow of steam into the turbine, the high-pressure regulating valve normally operates at small openings. Therefore, the phenomena such as whistling noise and turbulence can be caused by the throttling effect of the regulating valve. In addition, the flow-induced vibration due to coupling between the fluid flow and the moving parts like valve stem will also occur. In this paper, the pressure loss across the high-pressure regulating valve of a 600-MW ultra-supercritical steam turbine was assessed with the aid of computational fluid dynamics studies. Furthermore, the dynamic characteristics and vibration amplitude of the valve stem were also analyzed by using fluid–structure interaction method.

Numerical modeling and optimization of a power augmented S-type vertical axis wind turbine

ABSTRACT An axial symmetry augmented vertical axis wind turbine, which is suitable for arbitrary wind directions, is proposed in this paper. In order to improve the power generation ability of the S-type vertical axis wind turbine, a set of so-called “collection-shield boards” are installed symmetrically around the rotating S-type rotor. The flow fields around this type of wind turbine are numerically simulated with the aid of CFD method. The optimized design of geometrical parameters of the rotor and collection-shield boards is conducted by using the orthogonal design method. The obtained results suggest that the power output of the optimized augmented wind turbine can reach nearly three times higher than that of the conventional S-type vertical axis wind turbine.

Aerodynamic performance and characteristic of vortex structures for Darrieus wind turbine. II. The relationship between vortex structure and aerodynamic performance

In this paper, transient computational fluid dynamics (CFD) simulations of a straight-bladed Darrieus type vertical axis wind turbine were performed by means of an in-house CFD code. The Spalart-Allmaras turbulence model was implemented in the numerical code for the turbulence. Particular emphasis was placed on effect of interaction between vortices and blades on the aerodynamic performance of the simulated turbine at different tip speed and solidity ratios. The obtained results suggested that vortices were shed from previous blade passages and the close encounter of a rotor blade with these vortices can have a considerable impact on power coefficient of the simulated turbine during operation at different tip speed ratios. As a result, possible reasons for the changes in the behavior of this type of turbine due to the variation of tip speed ratio and solidity were proposed.