Thermography for Optimisation of Installed WindTurbines
Due to the decreasing number of suitable locations for wind turbines
and the increasing push towards renewable energy sources, newactivities have been introduced to improve the efficiency of rotor
blades for wind turbines.

Deutsche WindGuard Engineering GmbHwww.windguard.de
InfraTec solution:
ImageIR® 8300

The goal towards high efficiency is of great interest, because it has a direct impact on the achievable energy output ofwind turbines and thus, on the profit of the operator. Of course, the rotor blades of modern wind turbines have an
already optimised efficiency resulting from decades of aerodynamic research: their profiles are designed withsupercomputers and optimised in wind tunnels. In their production new technologies are applied, which were first
designed for the construction of high performance aircrafts. The goal of these measures is to have maximum
percentage as well as maximum controlling of laminar flow between the rotor surface and the surrounding air.
However, turbulent flows reduce the efficiency and therefore must be reduced to what is absolutely necessary.
In addition, there are many more factors that negatively affect the efficiency of wind power stations. It starts withalignment of the blades, leading edge contamination, erosion and damages to defective flow control add-ons, such asleading edge protection, vortex generators and zig-zag tape sections.
For several years now, thermography has been a valuable tool for investigating
the boundary layer behavior on airfoils in order to aerodynamically optimise it.
It makes use of the fact that the heat transfer resistance of the boundary layer
is significantly lower in turbulent flow than in laminar flow. For example, if thesurrounding air is colder than the rotor blade surface, a thermal pattern
appears on the surface which indicates the state of the flow. Because thetemperature on the turbulent flow region is colder than on the laminar low
region, measuring this thermal pattern with a thermal imaging camera permits
detecting the boundary layer condition in real-time.
Highly thermally sensitive high-speed infrared cameras with high performance
telephoto lenses are used to visualize the boundary layer condition of rotor
blades in operation, in which the rotor blades and the measurement position
are several hundred meters apart. These measurements deliver qualitative
information regarding the transition location along the rotor blades, and allow
comparisons between different operational states and conditions.

A high-speed actively cooled high-end infrared camera ImageIR® 8300 with an InSb-focal-plane array photon detector
in the format (640 x 512) IR pixels and with a thermal resolution better than 20 mK is used together with a telephotolens of 200 mm to acquire high resolution thermal images of rotor blades in operation. Due to extremely short
integration times, only minor motion blurs occur during tip speeds of 75 m/s.
Mit freundlicher Unterstützung von:C. Dollinger, N. Balaresque, M. Sorg: Thermographic Boundary Layer Visualisation of Wind Turbine
Rotorblades in Operation.
EWEA 2014, Bacelona, Spain: Europe’s Premier Wind Energy Event. EWEA The European Wind
Energy Association, Barcelona, 2014.

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