3D Simulation of a Vertical-Axis Wind Turbine
|關鍵字:||風力發電;垂直式風機;數值模擬;wind power;VAWT;numerical simulation|
A vertical-axis wind turbine which combines the merits of the lift type and drag type wind turbines is studied in this project. It consist of three S-type and two airfoil-type turbine blades. Several stages of these turbine blades can be stacked together to achieve better performance. The aerodynamic characteristics and performance are investigated by using computational fluid dynamic. The numerical scheme is based on the finite volume method. The moving mesh technique is adopted to tackle the rotation of the turbine wheel.With use of the RNG model to characterize turbulence, unsteady calculations are undertaken. Experiments are also conducted to assess the accuracy of the numerical simulation. Two-dimensional and three-dimensional, unsteady simulations are conducted. It is shown that the resulting moment coefficient becomes a linearly decreasing function of the tip speed ratio and the power coefficient is a quadratic function of the tip speed ratio. Comparison with experimental measurements for a one-stage wind turbine indicates that good agreement is obtained by the 3-D unsteady simulation. However, the torques and powers are over-predicted by the 2-D unsteady calculations. It can be detected from the results that after the flow passing the wind turbine, a periodic shedding vortex is formed in 2-D calculations while a relativity steady flow is observed in 3-D calculations. This implies that the flows beyond the upper and lower sides of the wind turbine have an effect of stabilizing the flow in the near wake of the turbine. This 3-D effect cannot be accounted for in 2-D calculations. Comparing with the single-stage wind turbine, only slightly higher power performance can be obtained by stacking several stages of turbines together. However, the variation of the torque with respect to time becomes smoother as the number of stage increase. This character helps stabilize operation of the wind turbine.