It is noted that in practice the term of blade pitch angle is usually referred to as [theta] at the hub section of the blade, but in this paper [theta] at the mid-blade height is used as the blade pitch angle in order to determine the shaft power matching.
After the blade pitch angle shown in Figure 2 is determined and the deviation angle is obtained from Figure 10, the distribution of [[beta].
As mentioned before, adjusting the blade pitch angle for CRAFF is burdensome due to lack of theoretical guidance.
In order to further discuss the effects of k, the approximate optimum blade pitch angle [[theta].
The authors analyzed the work done by two impellers of CRAFF using the method of velocity triangle and discovered that there exists a shaft power matching coefficient k, a tangent ratio of the relative outflow angles of two impellers, which not only determines the overloading of the rear impeller but also directly affects the flow rate and shaft power at design operation, the operation range of flow rate, and the blade pitch angle of the rear impeller.
Finally a guideline of shaft power matching for determining the approximate optimum of blade pitch angle of the two impellers is presented and applied to six different model fans for the same series of CRAFF.