Design of Airfoil as A Wind Turbine Blade

Design of Airfoil as A Wind Turbine Blade P M V Subbarao Professor Mechanical Engineering Department Anatomy of A Low Speed Lift Generator……

Aerodynamics of Airfoil as Wind Turbine Blade • For over 100 years, airfoil design has continued to capture the interest of practitioners of applied aerodynamics. • The field was fuelled by the ever-growing combination of airfoil design requirements for unique applications, such as wind turbine blades. • All possible permutations of the myriad of airfoil design requirements far exceeds the collection of existing airfoils. • Development of Various methods for airfoil design is the economical solution. • The objective of wind turbine blade design is known as the design of airfoils for High Lift at low Reynolds numbers. • This has been the subject of considerable research as documented in several major conferences and books.

Methods for Wind Turbine Blade Design • The direct blade design methods involve the selection of a standard NACA airfoil and the calculation of pressures and performance. • One evaluates the given shape and then modifies the shape to improve the performance. • The two main sub problems in this type of method are ; • the identification of the Figure of Merit (Fo. M). • the approach to changing the shape so that the performance is improved

Special Design Objectives • Generally, the objectives of blade design can be stated as: • To reduce the drag at high speeds while trying to keep the maximum Cl greater than a certain value. • Minimize Cd with a constraint on Clmax. • Define a Figure of Merit and Maximize Fo. M: • L/D or • Cl 1. 5/Cd or • Clmax / Cd @ Cldesign. • The selection of the figure of merit for airfoil sections is quite important and generally cannot be done without considering the rest of the cascade.

Generally used Airfoils for Wind Turbine Blades The NACA 0012 is a 12% thick symmetric airfoil. The NACA 63(2)-215 is a 15% thick airfoil with a slight camber, and the LS(1)-0417 is a 17% thick airfoil with a larger camber.

Inc rea sin g. A ngl eo f At tac k Angle of Attack vs Pressure distribution : Ideal Flow

Angle of Attack Vs Pressure distribution : Real Flow

Actual Performance of Airfoil (NACA 0012)

Selection of Operating Performance Curve CL CD

Demonstration of XFOIL By Ms Devi Mutyala

Airfoil : The Lift Machine • A significant difference in the performance between lift and drag machines is that much higher relative wind velocities can be achieved with lift machines. • Relative velocities are always greater than the free stream wind speed, sometimes by an order of magnitude. • The relative wind velocity at the airfoil of a lift machine is: • Speed ratios of up to 10, and forces proportional to the square of the relative speed, make the a lift machine to generate significantly greater force than a drag machine with the same surface area. • The larger forces allow for much greater power coefficients.

Essential Macro Design Steps Airfoil geometry

Design Methods • Direct design methods • Inverse Methods – Inverse Method via velocity distributions – Inverse viscous design • Design for performance

Direct Design Methods

Inverse Method via velocity distributions

Inverse viscous design

Design for performance

Wind speed distribution Vs Performance