Offshore Mechanics by unknow

Author:unknow
Language: eng
Format: epub
Published: 2018-04-02T00:00:00+00:00

Figure 4.17 shows the maximum power of a wind turbine as a function of the tip speed ratio. It can be seen that as the tip speed ratio increases, the maximum power becomes closer to the wind turbine’s Betz limit.

Figure 4.17 Comparison of power efficiency by considering or neglecting the rotational effects of a wind turbine. Dashed line shows the Betz limit in which rotational effects are neglected.

4.8.3 Blade Element Momentum Theory

In Sections 4.8.1 and 4.8.2, the induction factor was not known. We tried in this chapter to find the induction factor that leads to maximum power generation. Very often, we have a wind turbine with specific blades and shapes, and we are interested in computing the thrust force and torque moment on the wind turbine. To do that, we add the blade element theory to the momentum theory to find the relevant induction factor, and hence be able to calculate the thrust and torque on a wind turbine (Manwell et al., 2010).

First, we need to review the basic concepts regarding airfoil analysis. Figure 4.18 shows a wind turbine blade and an airfoil‐shaped cross section of it.

Figure 4.18 Wind turbine blade and cross section. Main characteristics of a cross section of a wind turbine blade are shown.

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