Wind Energy

PSD PSD
38 Unsteady Characteristics of Flow Around an Airfoil 213
0.5
0.4
0.3
0.2
0.1
f
0.0
0.0 0.5 1.0 1.5 2.0
* f = 1.2 Hz
* α = 20˚
= 0.16 Hz
f (Hz)
0.5
0.4
0.3
0.2
0.1
f
0.0
0.0 0.5 1.0 1.5 2.0
* f
=1.25 Hz
* = 0.16 Hz α = 40˚
f (Hz)
γ (s −1 )
γ (s −1 )
100
0
−100
α = 20˚
−200
0 3 6 9
t (s)
12 15
100
0
α = 40˚ a
−100
−200
−300
−400
b
0 2 4 6
t (s)
8 10 12
(a) PSD of the lift (b) Time history of γ from PIV
Fig. 38.2. Unsteady characteristics of (a) the lift and (b) the corresponding flow
field. The flow field unsteadiness is presented in terms of the time history of γ
(a)
(b)
y/c
y/c
1.4
1.2
1
0.8
0.6
0.4
0.2
1.4
1.2
1
0.8
0.6
0.4
0.2
1.39
0.35
.35
1.39
-1.14
-0.70
0.35
3.82
-1.74
0.78
-8.82
-0.70
0.39
1.39
0.70
1.14
-4.36
0.35
2.43
3.82-2.78 -1.74
-0.70
0.35
0.35
0.5 1 x/c
0.35
0.35
2.43
0.36
-2.78
-1.74
0.41 0.28 -4.86
1.38
3.47
-0.70
0.35
3.47
1.39
0.35
4.57
-0.70
0.35
-0.70
2.43
0.35
-0.70
-0.70-0.70
-0.70
-0.70
0.35
1.39
-0.70
4.51
2.43
-1.74
-0.70
-2.78
3.82
1.5
0.5 1
x/c
1.5
0.35
1.39
2.12-47
-0.70
0.35
-3.47 -3.47
4.51
-2.78
3.47
-1.74 -1.74
1.38 0.3
-1.74
0.36
4.51
1.39
-0.70
-4.86
-0.70
-2.78
-2.78
-3.82
0.36
0.35
3.47 4.52
0.36
-1.74-3.82
-0.70
-1.74
8.38 7.53
-0.70
-0.78
0.35
1.29 2.43
4.51
5.59
2.43
4.51
-4.86
-1.74
2.78
1.39
2.49
1.38
-0.7
3.47
2.43
1.38
-0.70
Fig. 38.3. The PIV vorticity field and the corresponding laser-sheet visualization
pictures around the airfoil at instant marked “a” and “b” in Fig. 38.2b at α =40 ◦
8.68
7.64
6.59
5.55
4.51
3.47
2.43
1.39
0.35
−0.70
−0.74
−2.78
−3.82
−4.86
−5.90
8.68
7.64
6.59
5.55
4.51
3.47
2.43
1.39
0.35
−0.70
−1.74
−2.78
−3.82
−4.86
−5.90
occurring at α = 40 ◦ [3] should be caused by the primary periodic
movement in the flow field.
3. For α ≥50 ◦ , although flow field is much more periodic, no perceptible
influence can be found in the corresponding PSD of force.
Figure 38.3 presents the vorticity field results of PIV and the corresponding
laser-sheet visualization pictures of the airfoil at different instant marked “a”