Wind Energy Handbook. Michael Barton Graham
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Название: Wind Energy Handbook
Автор: Michael Barton Graham
Издательство: John Wiley & Sons Limited
Жанр: Физика
isbn: 9781119451167
isbn:
Hence
which becomes
A great simplification can be made to Eq. (3.88) by ignoring the first term because, clearly, it disappears for much of the blade, where f = 1, and for the tip region the value of a′2 is very small. For tip speed ratios greater than 3, neglecting the first term makes negligible difference to the result:
As before, Eq. (3.60) still applies,
From Eq. (3.89),
Consequently,
which, combined with Eq. (3.89), gives
so
The radial variation of the average value of a, as given by Eq. (3.90), and the value local to the blade
Figure 3.36 Axial flow factor variation with radius for a three blade turbine optimised for a tip speed ratio of 6.
Clearly, the required blade design for optimal operation would be a little different to that which corresponds to the Prandtl tip‐loss factor because ab =
The blade design, which gives optimum power output, can now be determined by adapting Eqs. (3.70) and (3.71), noting that the left hand side of Eq. (3.70) refers to a local inflow angle at the blade, hence the factor becomes (1 – a/f):
Introducing Eq. (3.89) gives
The blade geometry parameter given by Eq. (3.91) is shown in Figure 3.37 compared with the design that excludes tip‐loss. As shown, only in the tip region is there any difference between the two designs.
Similarly, the inflow angle distribution, shown in Figure 3.38, can be determined by suitably modifying Eq. (3.73):
(3.92)
Again, the effects of tip‐loss are confined to the blade СКАЧАТЬ