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Sun X.,University of Shanghai for Science and Technology | Sun X.,Shanghai Key Laboratory of Power Energy in Multiphase Flow and Heat Transfer | Wang Y.,University of Shanghai for Science and Technology | Wang Y.,Shanghai Key Laboratory of Power Energy in Multiphase Flow and Heat Transfer | And 5 more authors.
Journal of Renewable and Sustainable Energy | Year: 2014

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-Darrieus turbine remains high power coefficient. If solidity is very low, the performance of a 2-bladed Darrieus turbine is obviously better than that of turbines with 3 and 4 blades. For moderate to high solidity, the power coefficients of the 2-bladed Darrieus wind turbine are similar to those of the 3-bladed turbine and are higher than those of the 4-bladed turbine. Moreover, the power coefficient increases with increasing solidity at low tip speed ratios. When the tip speed ratio is close to the optimum value, the power coefficient initially increases and then decreases with the increase of solidity. At high tip speed ratio, the power coefficient decreases with increasing solidity. An in-depth investigation is also conducted on the findings observed in this study and presented in Part 2 of this work, in which the mechanism of the effect of solidity on power coefficient has been explored based on the vortex structure of the flow field with the aid of this self-developed CFD code. © 2014 AIP Publishing LLC.


Sun X.,University of Shanghai for Science and Technology | Sun X.,Shanghai Key Laboratory of Power Energy in Multiphase Flow and Heat Transfer | Li X.,Shanghai University | Zheng Z.,University of Kansas | And 2 more authors.
Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy | Year: 2015

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. © IMechE 2015 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav.


Zhu B.,University of Shanghai for Science and Technology | Zhu B.,Shanghai Key Laboratory of Power Energy in Multiphase Flow and Heat Transfer | Han W.,Shanghai University | Sun X.,University of Shanghai for Science and Technology | And 8 more authors.
Journal of Renewable and Sustainable Energy | Year: 2015

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. © 2015 AIP Publishing LLC.


Wang Y.,University of Shanghai for Science and Technology | Wang Y.,Shanghai Key Laboratory of Power Energy in Multiphase Flow and Heat Transfer | Sun X.J.,University of Shanghai for Science and Technology | Sun X.J.,Shanghai Key Laboratory of Power Energy in Multiphase Flow and Heat Transfer | And 5 more authors.
Applied Thermal Engineering | Year: 2015

This paper numerically investigated the possibility of creating supercavitation through an artificially induced increase in the surface temperature of the underwater vehicle. Firstly, in order to consider the influence of thermomechanical effect on the cavitation process, the Zwart-Gerber-Belamri (ZGB) cavitation model was modified. By comparing with the experimental results, the accuracy of the modified model was validated. Secondly, the modified cavitation model was used to simulate the cavitating flows over a hemisphere cylinder body whose surface was heated to different temperatures. With the aid of CFD software ANSYS CFX, the variation of the bubble volume fraction and skin friction drag of the hemisphere cylinder at different cavitation numbers and heating temperatures were obtained and analyzed. The results show that the generation and development of cavity can be promoted by using the heating method. In this way, the friction resistance on underwater vehicle surfaces can be reduced effectively. There exists an optimal heating temperature to make the cavitation bubbles fully developed and cover the whole outside surface of underwater vehicle. By this means, the friction resistance on underwater vehicle surfaces can be reduced effectively, and the speed of vehicle can increase accordingly. © 2014 Elsevier Ltd. All rights reserved.


Sun X.,University of Shanghai for Science and Technology | Sun X.,Shanghai Key Laboratory of Power Energy in Multiphase Flow and Heat Transfer | Chen Y.,Nantong University | Cao Y.,Nantong University | And 4 more authors.
Advances in Mechanical Engineering | Year: 2016

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 Author(s) 2016.


Wang Y.,University of Shanghai for Science and Technology | Wang Y.,University of Newcastle | Wang Y.,Shanghai Key Laboratory of Power Energy in Multiphase Flow and Heat Transfer | Williams K.C.,University of Newcastle | And 2 more authors.
International Journal of Multiphase Flow | Year: 2016

A new frictional-kinetic model is proposed and modified for pressure drop prediction of alumina in a bypass pneumatic conveying system. This new model is based on the conventional Johnson-Jackson frictional-kinetic model. The critical value of solids volume fraction and maximum packing limit are modified based on the fluidized bulk density and tapped bulk density, respectively. In addition, an offset solid volume fraction is introduced into the frictional pressure model as well as into the radial distribution functions which represents the correction factors to modify the probability of collisions between particles when solid phase becomes excessively dense. For the application of the model, computational fluid dynamics (CFD) simulations were conducted by using kinetic theory, conventional frictional-kinetic model and modified frictional-kinetic model. The simulation results were then compared with the experimental results. It was found that the modified frictional-kinetic model showed the largest improvement on pressure drop prediction results compared with results obtained from applying the kinetic theory and the conventional frictional-kinetic model, especially for denser flows with low air mass flow rates and high solid loading ratios (SLR). In addition, the solids volume investigation of CFD simulations shows a strong comparison to the actual flow conditions in the pipe, as transient slug type flow of alumina is observed. © 2015 Elsevier Ltd.

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