Page 184 - Fluid Mechanics and Thermodynamics of Turbomachinery

Axial-flow Compressors and Fans 165
where is the angle between the flow direction and line of zero lift of the aerofoil.
For an isolated, cambered aerofoil Wislicenus (1947) suggested that the zero lift line
may be found by joining the trailing edge point with the point of maximum camber
as depicted in Figure 5.18a. For fan blades experiencing some interference effects
from adjacent blades, the modified lift coefficient of a blade may be estimated by
assuming that Weinig’s results for flat plates (Figure 5.15) are valid for the slightly
cambered, finite thickness blades, and

C L D 2 k sin . (5.41a)
When the vanes overlap (as they may do at sections close to the hub), Wisli-
cenus suggested that the zero lift line may be obtained by the line connecting the
trailing edge point with the maximum camber of that portion of blade which is not
overlapped (Figure 5.18b).
The extension of both blade element theory and cascade data to the design of
complete fans is discussed in considerable detail by Wallis (1961).

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