Thumbnail Image

Analysis of Low-Induction Rotors for Increased Power Production

Wind turbine aerodynamics are characterized by several coefficients, most notably the thrust, power, and axial induction, which is the fractional decrease of the free stream wind speed to the rotor plane. Current turbine designs aim to maximize these coefficients to reach what is generally considered to be maximum aerodynamic efficiency. Such rotors are referred to as a Betz-optimal rotor. This thesis examines a new method called “Low-Induction Rotors (LIR)” for increasing aerodynamic efficiency by decreasing the thrust loading of the blade. A family of low induction rotors (LIRs) can be derived from a reference wind turbine (RWT) by using the root bending moment as a constraint. Using the root bending moment of the RWT and imposed loading, new rotor lengths are derived. The family of low induction rotors are characterized by lower thrust loading across the blade. Prandtl’s bell shaped loading distribution was used to define the distribution of spanwise thrust since it is better fit for long-thin airfoils. Momentum Theory and Blade Element and Momentum theory were used to solve for the rotor power coefficient in two different ways, either including or excluding tip-losses. The family of rotors was then analyzed to determine power output. It was found that more power was produced as the rotor length increases and thrust loading decreased. The National Renewable Energy Lab’s AeroDyn software was used to conduct cp-λ sweeps on 6 selected rotors (128m, 137m, 147m, 156m, 167m, and 177m) to determine how power output was affected by changes in wind speed. The cp-λ analysis showed that the longer rotors with lower induction were less sensitive to changes in wind speed. The low induction rotors minimized a change in the coefficient of power as the pitch and tip speed ratio were changed. Low induction rotors are a promising field of wind energy, while maintaining the forces are the turbine hub, longer rotors with lower aerodynamic loading can be used to generate a more stable power supply.
Research Projects
Organizational Units
Journal Issue
Publisher Version
Embedded videos