Chapter 4: Wind Turbine
Self-Sustaining Street Light
aerodynamics governing the rotation are less complicated) and the fact that LED lights (the type of lights under investigation for this light post design) maintain low power requirements.
Fig. 4.1. Power coefficient curves for various wind turbine designs [4.1].
4.2 Savonius Rotor Principles As explained previously, Savonius rotor designs function through the application of drag forces. From fundamental fluid mechanics, it is known that the drag force on an object can be defined through the use of a drag coefficient, as shown in (4.1). From (4.1), it can be deduced that for objects of equivalent area and in similar flow conditions (density, velocity), that a higher value of drag coefficient, CD, will correspond directly to a higher value of drag force, D. A Savonius design implements two semicircular buckets to create a difference in drag forces. This difference in drag forces, DRETREATING and DADVANCING (for retreating and advancing buckets, as shown in Fig. 4.1), is created by the difference in relative values of CD: C D , RETREATING ≈ 2.3 ;
C D , ADVANCING ≈ 1.2 [4.2]. D=
1 ρV 2 AC D 2
(4.1)
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