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.
Search WWH ::
Custom Search