Читать книгу Wind Energy Handbook - Michael Barton Graham - Страница 121

The remaining three sources of aerodynamic blade self‐noise are usually less significant than i) above involving interaction between the turbulent boundary layers and a sharp trailing edge:

 ii) Noise due to locally separated flow is more usual from the inner blade where intensities are limited by low relative velocities. Significant separation is unusual on the outer blade under low to moderate wind conditions for which blade noise may be a concern.

 iii) Noise due vortex shedding from the trailing edge of the blade can be of concern. It should be considered only if the outer blade aerofoil section has a particularly blunt trailing edge. If it occurs, it can be more irritating than purely broadband noise because of the strong tonal content.

 iv) Tip vortex noise does not seem to be particularly well understood but can be minimised by a well‐designed tip with appropriate rounding.

Figure 3.78 Low noise aerofoil family: (a) DTU‐LN1xx, (b) DTU‐LN2xx, and (c) DTU‐LN3xx.

Source: From Zhu, Shen, and Soerensen (2016).

Figure 3.79 Diagram of serrated trailing edge for reduction of TE noise.