TY  - GEN
Y1  - 2021///
TI  - Investigation of the water-sided shear
layer at a wind-driven wavy surface
by active thermography
CY  - Heidelberg
AV  - public
ID  - heidok30834
UR  - https://archiv.ub.uni-heidelberg.de/volltextserver/30834/
A1  - Voigt, Philipp Immanuel
N2  - A local, active thermographic measurement method was advanced and used for measuring
the mean viscous shear stress in the water-sided boundary layer of a wind driven air-water
interface in the presence of water waves, at low wind speeds up to u 10 = (4.8 ± 0.3) m/s.
Higher wind speeds of up to u 10 = (10.7 ± 0.7) m/s were considered to explore the
boundaries of the application of the method. The measurements were conducted at
the annular wind-wave facility Aeolotron in Heidelberg, Germany. The measurement
technique utilizes a thin line which is heated onto the surface perpendicular to the wind
direction. The broadening of the line is enhanced by Taylor dispersion due to shear flow
in the boundary layer. The temporal development of the line width is monitored by
an infrared camera. The broadening is compared to numerically simulated line widths,
enabling the determination of the viscous shear stress. This initial study with a rough
surface showed promising results for both the evaluation of longer time intervals, and
temporally resolved measurements on the order of few seconds. Stationary conditions
with the air and water compartments in dynamical equilibrium, corresponding to a quasi-
infinite fetch, and non-stationary conditions after turning the wind on were considered.
The stationary results were compared to results for the viscous shear stress obtained by
water-sided particle streak velocimetry, with results deviating by less than 15%. The
non-stationary measurements indicated an overshoot in the viscous shear stress shortly
after turning the wind on.
ER  -