Computational fluid dynamics study of wind turbine

• Main Author: Tang, Jiann Haur.
• Other Authors: Zhao Yong
• Format: Final Year Project
• Language: English
• Published: 2009
• Subjects: DRNTU::Engineering::Mechanical engineering::Fluid mechanics
• Online Access: http://hdl.handle.net/10356/16860
• Institution: Nanyang Technological University

Principle of energy conversion of wind turbine can be understood from momentum theory. Betz limit sets the upper limit of power coefficient. Blade element momentum (BEM) theory enables optimization of blade design. Blade geometry parameter and inflow angle are basic results from the solution of BEM equations. Chord length ratio and pitch angle are derived to be used in blade design. Discrepancies from Betz limit are caused by aerodynamic drags and finite numbers of blades. Prandlt tip loss factor accounts for non-uniform axial induction factor caused by finite-blade effect. Radial flow and tip/root vortex are three-dimensional (3D) flow related to rotating blade. Radial flow is driven by centrifugal force under separated flow condition while tip/root vortex is inherent in discrete blade. Computational fluid dynamics analysis of the design blade showed that radial flow is prominent near the boundary viscous layer at the suction inboard side. Strength of tip/root vortex increases as wind speed increases. Discrepancies in power coefficient are related to stall drag at low tip speed ratio and turbulence drag at high tip speed ratio. Design tip speed ratio is merely in agreement with optimum tip speed ratio of power coefficient, possibly caused by Coriolis effect, another 3D property comes along with radial flow, thereby causing stall-delay of blade. Aerodynamics, centrifugal and gravity forces are three fundamental loads govern the structural design of rotating blade. Finite element model is used to analyze structural design of skin with spar section. Simulation showed that maximum deformation at tip section and maximum stress at root section occurred at swept angle of 90°. Asymmetry distribution of blade mass introduces tip deflection in edgewise, spanwise and flapwise direction. Cyclic flapwise deflection is caused by gravity. Aerodynamics deformation is more dominant in total deformation while centrifugal stress is more dominant in equivalent stress relative to gravity effect. Although spar design introduces extra force and moment reaction on root, its structural strength and rigidity is improved.