Tip-speed ratio

The tip speed ratio λ (lambda) is an important metric for the design of wind turbines ( WT ). It gives the ratio of the circumferential speed U of the rotor for the wind speed and is defined as ν

R = radius of the rotor, = angular speed of the rotor and n is the rotor speed. The reciprocal value of the tip speed ratio is known in turbine and the propeller theory as a progress degrees.

Resistance Runner, such as historical windmills, have a tip speed ratio not less than one and are considered here.

From the tip speed ratio and the most flatter outward setting angle gives the angle of the flow to the blade profile. Since both the momentum flux of the wind, which it slowing down to about 2/3 applies ( Betz 's law), as well as the aerodynamic forces about quadratic increase with the flow velocity, the speed ratio is almost independent of the wind speed for a constant harvest level.

According to the tip speed ratio is divided into slow-moving with a speed ratio of about 1-3, and high-speed with a speed ratio of about 5 to 7 .. 8 Wind turbines with a tip speed ratio greater than 10 ( one-and two -bladed rotors ) are no longer built, among other things because of the high acoustic emission today usually.