Wind Energy

108 Karine Leroux and Olivier Eiff
(a) 2.0
n=H
1.5
1.0
0.5
0.0
0 1 2 3 4
(b)
2.0
s=H
n=H
1.5
1.0
0.5
0.0
H
0 . 6H
0 1 2 3 4
s=H
Fig. 18.3. Boundary layer representation. | −→ U |/U0 for Re ∼ 10 2 (a), and Re ∼ 10 4
(b)
nevertheless some differences between the two cases. The TLW train of wavelength
0.8λ is shifted downstream by 0.3H in the slip case, resulting in a
shifted extend of the separated downslope windstorm, in phase with the wave
train.
18.5 Boundary Layer and Wave Field Interaction
In Figs. 18.3a and b for Re ∼ 10 2 and Re ∼ 10 4 , respectively, the norm of
the velocity field | −→ U | /U0 is plotted on a (s/H, n/H) chart, on the lee
side. n is the perpendicular height from surface, and s is the surface-following
coordinate starting on the obstacle crest. The thickness of the high velocity
region defined as | −→ U |> U0 is 40% smaller at high Re-number, but in both
cases the maximum velocity is located at a distance of 0.4H above the obstacle
near x = λ/3. If the obstacle were a flat plate, the boundary-layer height
δ/H would be approximately proportional to 1/H for the flow parameters
of the two cases. Considering Umax to delimit the boundary-layer height on
the obstacles, they do not scale as standard boundary layers, implying, as
expected, a strong wave-field influence. The Re-number independence suggests
a one-way interaction of the wave field on the boundary-layer height.
2.5
2.0
1.5
1.0
0.5
0.0