Lixun Zhang

Aerodynamic Performance Prediction of Straight-Bladed Vertical Axis Wind Turbine Based on CFD

Numerical simulation had become an attractive method to carry out researches on structure design and aerodynamic performance prediction of straight-bladed vertical axis wind turbine, while the prediction accuracy was the major concern of CFD. Based on the present two-dimensional CFD model, a series of systematic investigations were conducted to analyze the effects of computational domain, grid number, near-wall grid, and time step on prediction accuracy. And then efforts were devoted into prediction and analysis of the overall flow field, dynamic performance of blades, and its aerodynamic forces. The calculated results agree well with experimental data, and it demonstrates that RNG k-ε turbulent model is great to predict the tendency of aerodynamic forces but with a high estimate value of turbulence viscosity coefficient. Furthermore, the calculated tangential force is more dependent on near-wall grid and prediction accuracy is poor within the region with serious dynamic stall. In addition, blades experience mild and deep stalls at low tip speed ratio, and thus the leading edge separation vortex and its movement on the airfoil surface have a significant impact on the aerodynamic performance.

Vertical Axis Wind Turbine with Individual Active Blade Pitch Control

Increasing attention has been paid on Vertical Axis Wind Turbine (VAWT) to improve the poor aerodynamic performances. In this paper, we obtain the aerodynamic coefficients of blades by the method of simulation and experiments, and present along with a prototype of Variable-pitch VAWT. Then, mathematical model and dynamic model have been built, and individual active control for computing the optimal pitch angle of VAWT has been presented, which can maximize its power output at given operational conditions. Based on simulation, comparative analysis between fixed-pitch and individual active variable-pitch of prototype have been done. We have found that aerodynamic performances have been greatly improved, tangential force coefficient of which is twice as large as that of fixed-pitch VAWT. Moreover, an optimum active variable-pitch control strategy which is reliable and efficient has been proposed to achieve a better operation condition.