Wind turbine having flow-aligned blades

Abstract

A wind turbine blade is configured such that the lift force from the blade airfoil is always normal, or nearly normal, to the shaft torque. This condition maximizes energy conversion. This objective may be achieved by a) having the airfoil chord always aligned to the actual wind direction (subject only to small angle of attack variations), and b) slowing the turbine rotation rate so that no blade twist is needed. As a result, blade tip speed due to shaft rotation is less than the wind speed, and preferably much less. This low tip speed eliminates any hazard to birds. The lift force from the blade airfoil directly drives the torque on the shaft, so the control problem simplifies to adjusting the blade angle of attack to keep the lift constant across varying wind speeds. For most airfoils, a slightly negative angle of attack results in zero lift, so this simple approach has a ready fail-safe condition. This fail-safe condition is operable up to very high wind speeds, eliminating any need to provide for turbine overspeed control. The same teachings are equally applicable to water turbines and other types of turbines.