High speed number

This article deals with the high speed number of caseless wind turbines, for the high speed number of "cased" turbo machines see running number .

Performance coefficient over the high speed number, number of blades

The high speed number  λ (lambda) is an important key figure for the design of wind power plants  (WKA). It gives the ratio of the circumferential speed  u of the rotor to the wind speed  ν :

${\displaystyle \lambda ={\frac {u}{\nu }}={\frac {\omega _{r}\cdot r}{\nu }}={\frac {2\pi n\cdot r}{\nu }}}$

With

• r = rotor radius
• ${\displaystyle \omega _{r}}$= Angular speed of the rotor
• n = rotor speed .

The reciprocal value of the high speed number is known as the degree of progress in turbine construction and in propeller theory .

A distinction is made according to the high speed number:

• Slow runners with a high speed number between 1 and 3
• High-speed runners with a high-speed number between 5 and 12.

Resistance runners , for example historical windmills , have a high speed number less than one and are not considered here.

The angle of attack of the flow in relation to the blade profile results from the high speed number and the setting angle which becomes flatter towards the outside . Since the impulse current of the wind can be slowed down by a maximum of about 60% ( Betz's law ) and since the wind forces on the wing increase roughly quadratically with the flow speed, the high speed rate is almost independent of the wind speed for a constant degree of harvest .

literature

• Robert Gasch , Peter Bade, Jochen Twele: Wind turbines: Basics and design . In: Robert Gasch (Ed.): Textbook mechanical engineering . No. 4 . Vieweg + Teubner Verlag , 2005, ISBN 978-3-519-36334-7 , Chapter 3.1: Rotor, p. 55 ( Book Preview [accessed June 26, 2009]).