Fluid Mechanics and Thermodynamics of Turbomachinery, 5e

356 Fluid Mechanics, Thermodynamics of Turbomachinery
C X
0.8
0.6
0.4
0.2
1
2
C L = 1.0
0.8
0.6
3 4 5 6 7
Tip–speed ratio, J
FIG. 10.17. Variation of the axial force coefficient Cx vs tip–speed ratio J for three
values of the lift coefficient, C L = 0.6, 0.8 and 1.0.
Power coefficient, C P
0.5
0.4
0.3
0.2
0.1
0
1
2
C L = 1.0
0.8
3 4 5 6 7
Tip–speed ratio, J
FIG. 10.18. Variation of the power coefficient CP vs J for three values of the lift
coefficient, C L = 0.6, 0.8 and 1.0.
Rotor optimum design criteria
Glauert’s momentum analysis provides a relatively simple yet accurate framework
for the preliminary design of wind turbine rotors. An important aspect of the analysis
not yet covered was his development of the concept of the “ideal windmill” which provides
equations for the optimal rotor. In a nutshell, the analysis gives a preferred value
of the product CLl for each rotor blade segment as a function of the local speed ratio j
defined by
0.6