Title:

TNO boundary layer tunnel. Quality of velocity profiles.


Author(s):



Published by:

Publication date:

ECN
Wind Energy

152005


ECN report number:

Document type:

ECNC05050

ECN publication


Number of pages:

Full text:

28

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Abstract:
Thevelocity profiles and Reynolds stresses of the empty boundary layer
tunnel of TNO Apeldoorn have been characterized. This tunnel has a measurement
section of 3 m wide, 2 meters high, and 9 meters long. The tunnel was
set up to represent an offshore atmospheric boundary layer scaled by
a factor of 400. The measurements were carried out by a hotwire traverse
system. The results are listed below.
characteristic

neutrally stable, offshore atmosphere in reality

empty TNOtunnel (69 m/s)

vertical velocity profile

logarithmic

logarithmic up to 80 cm height (320m
on scale) over first 9 m (3600m on scale);
separate fits of lower 17 cm yield
25% larger values for u_{*}.

horizontal velocity profile

flat

varies by 3% over tunnel width between
17 and 37 cm height (68m  148m on scale)

friction velocity u_{*}

constant

varies by 9% over first 9 meters

shear stress
(Reynolds stress, <u'w'>)

'independent' of height

'independent' of height in first
4.5 meters.
decreases about 30% in 80 cm height in next 4.5 meters.

surface roughness z_{0}

0.2 mm

0.47.2*10^{4 }mm (0.020.3
mm on scale)

dynamic pressure gradient in wind
direction dP/dx

'none'

» 0.5 Pa/m (1.3^{ }Pa/km
on scale)

We conclude
that the test section of the tunnel represents offshore conditions well
in an onscale area ranging from sea level to 320 m altitude and extending
over 3.6 km in flow direction.
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