Date on Master's Thesis/Doctoral Dissertation

8-2011

Document Type

Master's Thesis

Degree Name

M.S.

Department

Mechanical Engineering

Committee Chair

Lian, Yongsheng

Author's Keywords

CFD; H-rotor

Subject

Wind turbines--Aerodynamics; Wind turbines--Research; Fluid dynamics

Abstract

Vertical axis wind turbines (VAWTs) are devices to convert wind energy into electricity. Unlike horizontal axis wind turbines (HAWT) where the main rotor shaft is set horizontally, VAWTs use vertical rotor shaft. Unlike HAWTs, VAWTs can be effectively used in urban environment where flow is characterized with unsteadiness and turbulence. The efficiency of the VA WTs highly depends on the aerodynamics of the wind blades. In this thesis we study the aerodynamics of the H-rotor, one type of VAWTs using computational fluid dynamics methods. Two different approaches are used in this study. One is based on direct numerical simulation (DNS) method and another is based on Reynolds averaged Navier-Stoke (RANS) model. For DNS study we solve the incompressible Navier-Stokes equations with a CFD package, OVERTURE. An overlapping moving grids technique is employed to handle the rotation of the wind turbine. For RANS simulation we used a commercial CFD package ANSYS-Fluent. The sliding mesh model of ANSYS-Fluent is applied to evaluate unsteady interaction between the stationary and rotating components. Our simulation shows that the DNS cannot correctly predict the power coefficient due to the lack of grid resolution at high Reynolds numbers. The RANS simulation results closely match the experimental data and RANS provides a way to study wind turbine aerodynamics in an efficient and reliable manner. Our simulation shows that the rotor with NACA0015 blade section obtains a maximum power coefficient of 0.16 at tip speed ratio of 2.5 for mean wind velocity of 3.9m/s. By replacing the blade section with NACA0022 airfoil profile, the maximum power coefficient of the rotor can be improved to 0.21 at tip speed ratio of 2.5 in the same wind conditions.

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