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ECN publication
TNO boundary layer tunnel. Quality of velocity profiles.
Published by: Publication date:
ECN Wind Energy 1-5-2005
ECN report number: Document type:
ECN-C--05-050 ECN publication
Number of pages: Full text:
28 Download PDF  


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.



neutrally stable, offshore atmosphere in reality

empty TNO-tunnel (6-9 m/s)

vertical velocity profile


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


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

friction velocity u*


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 z0

0.2 mm

0.4-7.2*10-4 mm (0.02-0.3 mm on scale)

dynamic pressure gradient in wind direction dP/dx


» -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 on-scale area ranging from sea level to 320 m altitude and extending over 3.6 km in flow direction.

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