Environmental Engineering Reference
In-Depth Information
Fig. 4.5 a High-angle lift
coefficients for Reynolds
numbers above 2 9 10 5 .
b High-angle drag
coefficients for Reynolds
numbers above 2 9 10 5 . Data
sources listed in Table 4.2
(a)
1.2
1
0.8
C l = 2sin
αα
cos
0.6
0.4
0.2
0
20
30
40
50
60
70
80
90
angle of attack (
°
)
(b)
2.5
2
1.5
C d = 2sin 2
1
α
0.5
0
20
30
40
50
60
70
80
90
angle of attack (
°
)
Table 4.2
Source of data for Fig. 4.5
Symbol
Source
Aerofoil
Re
7.6 9 10 5
+
Michos et al. [ 8 ]
NACA 0012
5 9 10 5
O
Sheldahl and Klimas [ 7 ]
NACA 0012
5 9 10 5
9
Sheldahl and Klimas [ 7 ]
NACA 0015
4 9 10 5
D
Devinant et al. [ 10 ]
NACA 65 4 -421
2.5 9 10 5
h
Ostawari and Naik [ 9 ]
NACA 4415
2.5 9 10 5
Ostawari and Naik [ 14 ]
NACA 4418
2 9 10 5
*
Bruining [ 15 ]
Cambered flat plate
Another way to view the data is to assume that the lift and drag arise almost
entirely from the pressure distribution on a thin flat plate or aerofoil at high angles.
Then the lift:drag ratio must equal 1/tan a. A test of this is shown in Fig. 4.7 which
shows significant departures at low Re. The decrease in C l with decreasing Re at
moderate a seems, therefore, to be more significant than that in C d . The increasing
viscous stress on the aerofoil as Re decreases will tend to increase the drag and
decrease the lift.
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