Effect of abrasion and biofoulingon aerodynamic performanceof industrial surface coatings
F. Gökhan Ergin, CTA Product Manager, Dantec Dynamics, Copenhagen, Denmark. gokhan.ergin@dantecdynamics.com

Experimental setup

Boundary layer measurements

Fig 1a Computer controlled, 3-axis traverse
system mounted on the DTU wind tunnel.

Fig 2a The flat plate schematic, the assumed
coordinate system and the measurement plane.

Fig 1b Back side of the flat panel during
zero-pressure-gradient alignment.

Fig 2b Hotwire probes during boundarylayer measurements.

Effect of abrasion and biofouling on the aerodynamic
performance of industrial surface coatings is investigated. The test section of the DTU closed-loop windtunnel (Fig. 1a) is refurbished to perform automatedboundary layer stability experiments. The new test
section features a sliding front window, a computercontrolled three-axis traverse, angle of attack adjustment, zero-pressure-gradient alignment (Fig 1b), quick
test plate replacement and repeatable alignment
between plates. In total 11 flat plates were used inpristine, abraded and biofouled states. The measurements were performed using a Dantec DynamicsStreamLine Pro Hotwire Anemometry System with anautomatic velocity calibrator, system PC, StreamWare
Pro software and a custom-developed LabVIEW
program. StreamWare Pro was used for system setup
and velocity calibration process, and LabVIEW
programs were used for measuring laminar andturbulent velocity profiles. A National Instruments 4channel simultaneous sampling differential USB A/D
converter was used. A Dantec 55P15 boundary layerprobe and a Dantec 55P11 freestream probe werepositioned at multiple grid points using a computercontrolled 3-axis traversing system. Since thetemperature in the test section may rise as much as
5°C during the course of the measurements,
temperature correction was performed using acorrection procedure suggested by Benjamin andRoberts [1]. Voltages were corrected according to:

Boundary layer profile measurements were taken at 4measurement planes (Fig. 2a) for each plate; 125mm,250mm, 375mm and 500mm from the plate leadingedge. Two single-normal sensor probes are mounted
on the traversing mechanism using the hotwire
support arm (Fig. 2b). Boundary layer velocity values
were normalised with the freestream velocity values
in order to minimize the effect of freestream speed
fluctuations. The boundary layer type was identified
for each plane before the actual experiment bymeasuring a boundary layer profile on each edge andin the middle. The measurement height was set toeither η=8 (laminar) and η=16 (turbulent) dependingon the boundary layer type. Corrections of arbitrarywall normal coordinates were performed according
to White and Ergin [2]. Wall position at each spanwise
location is estimated by fitting a line to the velocity
profile between data points where the velocity is 18%
and 30% of the freestream velocity, Ufs; andextrapolating to zero velocity. Then a quadratic fit isperformed on the wall positions vs. spanwise
coordinate (y vs z) and this information is used forcorrecting the wall-normal positions of the acquired
data. Due to the presence of distributed roughness,
all spanwise positions were used for the quadratic fit.
This is useful in two aspects: first the number of data
points is increased for a better wall location estimate,and second this approach provides an unambiguous
definition of an effective wall surface in the presenceof distributed roughness. Finally the data files are
saved in .txt format compatible with Tecplot. Bothlaminar and turbulent profiles were observed duringexperiments, but results of only two plates arereported where a combination of both flow fields areobserved.

 T T Vc  Vm 1  c x  Tw  Tx 0.55

where Vc is the corrected voltage, Vm is the measured
voltage, Tc is the calibration temperature, Tw is the wire
temperature and Tx is the elevated ambient
temperature during measurements.

Fig 3 Turbulent flow field over 2I coating in
Pristine (top) and Biofouled (bottom) state.
A success criterion is defined for the aerodynamic
performance: If the coating can produce a laminarboundary layer in its pristine state and can keep thistype of flow in its aged state, the coating is successful.
In contrast, if a coating cannot produce a laminarboundary layer profile in its pristine condition or keep
it in its aged condition, then the coating is not
successful:› Coating 2 which does not contain nanoparticles is
the most successful since it is able to produce alaminar boundary layer and keep this flow
condition in its aged state (both biofouled andabraded).
› Coating 2O and 2R are successful since they areable to produce a laminar boundary layer and keep
this flow condition in their abraded state. Since
these panels were not bio fouled, no definitive
conclusion can be made on their success in thebiofouled state.
› Coating 2I is unsuccessful as it produces aturbulent boundary layer in its pristine and aged
state (Fig. 3). Since this panel was not abraded nodefinitive conclusion can be made on its success inthe abraded state.

Acknowledgments
European Union Seventh Framework Program (FP72007-2013) under grant agreement number 310397.
The author wishes to thank, Prof. Knud Erik Meyer,
Prof. Edward B. White and Allan Kruse Christensen.

REFERENCES[1] SF Benjamin, CA Roberts “Measuring flow velocity at elevated temperature with a hot wire anemometer calibrated in cold flow” Int. J. Heat & Mass Transfer 45(2002)703–706[2] EB White, FG Ergin “Using laminar-flow velocity profiles to locate the wall behind roughness elements” Experiments in Fluids 36 (2004) 805–812

Poster SP_0515_v1. Subject to change without notice.
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