Measurement uncertainty of IR thermographic flow visualization measurements for transition detection on wind turbines in operation

Dollinger, Christoph; Sorg, Michael; Balaresque, Nicholas; Fischer, Andreas

doi:10.1016/j.expthermflusci.2018.04.025

Cited by 38 publications

(32 citation statements)

References 29 publications

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“…Surface areas with laminar flow appear comparatively warmer in the thermographic image than surface areas with turbulent flow. This enables a distinction of the boundary layer flow areas and a localization of the laminar-turbulent transition, which can be realized by image processing algorithms [22,23]. Furthermore, advanced image processing methods enable the identification of flow separations [24].…”

Section: Thermographymentioning

confidence: 99%

“…The localization of the laminar-turbulent transition is performed by an approximation of the chordwise temperature profile on the rotor blade surface with a Gaussian cumulative distribution function. The approximation allows the determination of the transition position with subpixel accuracy [22]. By taking into account the position of the aerodynamic glove in relation to the thermographic camera, the visible surface area could be assigned to its geometry.…”

Section: Thermographic Setup Provided By Bimaq and Dwgementioning

confidence: 99%

“…As an example, the results from 11:15:32 and 10:16:45 (SCADA time) are shown. Figure 14 shows the transition position (Team BIMAQ and DWGE uses location of maximum temperature gradient to locate a transition point) derived by the image-processing algorithm from Dollinger et al [22] for the SU phase of the WT. On the left side, the thermographic image with the visible LE and TE, as well as derived relative transition position p tr , are shown.…”

Section: Thermography Team Bimaq and Dwgementioning

confidence: 99%

See 2 more Smart Citations

Investigation of Laminar–Turbulent Transition on a Rotating Wind-Turbine Blade of Multimegawatt Class with Thermography and Microphone Array

et al. 2019

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Knowledge about laminar–turbulent transition on operating multi megawatt wind turbine (WT) blades needs sophisticated equipment like hot films or microphone arrays. Contrarily, thermographic pictures can easily be taken from the ground, and temperature differences indicate different states of the boundary layer. Accuracy, however, is still an open question, so that an aerodynamic glove, known from experimental research on airplanes, was used to classify the boundary-layer state of a 2 megawatt WT blade operating in the northern part of Schleswig-Holstein, Germany. State-of-the-art equipment for measuring static surface pressure was used for monitoring lift distribution. To distinguish the laminar and turbulent parts of the boundary layer (suction side only), 48 microphones were applied together with ground-based thermographic cameras from two teams. Additionally, an optical camera mounted on the hub was used to survey vibrations. During start-up (SU) (from 0 to 9 rpm), extended but irregularly shaped regions of a laminar-boundary layer were observed that had the same extension measured both with microphones and thermography. When an approximately constant rotor rotation (9 rpm corresponding to approximately 6 m/s wind speed) was achieved, flow transition was visible at the expected position of 40% chord length on the rotor blade, which was fouled with dense turbulent wedges, and an almost complete turbulent state on the glove was detected. In all observations, quantitative determination of flow-transition positions from thermography and microphones agreed well within their accuracy of less than 1%.

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Section: Thermographymentioning

confidence: 99%

Section: Thermographic Setup Provided By Bimaq and Dwgementioning

confidence: 99%

Section: Thermography Team Bimaq and Dwgementioning

confidence: 99%

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Investigation of Laminar–Turbulent Transition on a Rotating Wind-Turbine Blade of Multimegawatt Class with Thermography and Microphone Array

et al. 2019

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“…In the most general sense, every surface property induces a flow feature which implies a certain convective cooling or heating, hence being potentially recognizable in a thermogram. In visualization of wall-bounded flows, IRT provides a spatial accuracy in the subpixel range which is in practice limited by remaining unsteadiness of the flow itself (Dollinger et al, 2018b). More details about the underlying physical theory of IRT and a selection of applications are given by Carlomagno and Cardone (2010).…”

Section: Introductionmentioning

confidence: 99%

Remote surface damage detection on rotor blades of operating wind turbines by means of infrared thermography

et al. 2018

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Abstract. Wind turbines are constantly exposed to wind gusts, dirt particles and precipitation. Depending on the site, surface defects on rotor blades emerge from the first day of operation on. While erosion increases quickly with time, even small surface defects can affect the performance of the wind turbine. Consequently, there is demand for an easily applicable remote monitoring method for rotor blades that is capable of detecting surface defects at an early stage. In this work it is investigated if infrared thermography (IRT) can meet these requirements by visualizing differences in the thermal transport and the corresponding surface temperature of the wall-bounded flow.Firstly, a validation of the IRT method compared to stereoscopic particle image velocimetry measurements is performed comparing both types of experimental results for the boundary layer of a flat plate. Then, the main characteristics of the flow in the wake of generic surface defects on different types of lifting surfaces are studied both experimentally and numerically: temperature gradients behind protruding surface defects on a flat plate and a DU 91-W2-250 profile are studied by means of IRT. The same is done with the wall shear stress from Reynolds-averaged Navier–Stokes simulations of a wind turbine blade. It is consistently observed, both in the experiments and the simulations, that turbulent wedges are formed on the flow downstream of generic surface defects. These wedges provide valuable information about the kind of defects that generate them. At last, experimental and numerical performance measures are taken into account for evaluating the aerodynamic impact of surface defects on rotor blades. We conclude that the IRT method is a suitable remote monitoring technique for detecting surface defects on wind turbines at an early stage.

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“…Fig. 13shows the transition position derived by the image processing algorithm from Dollinger et al[24] for the start upphase of the wind turbine. On the left side the thermographic image with the visible leading (LE) and trailing edge (TE) as well as the derived relative transition position p tr are shown.…”

mentioning

confidence: 99%

Investigation of Laminar-Turbulent Transition on a Rotating Wind Turbine Blade of Multi Megawatt Class with Thermography and a Microphone Array

Reichstein¹,

Schaffarczyk²,

Dollinger³

et al. 2019

Preprint

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Knowledge about laminar-turbulent transition on operating multi-megawatt wind turbine blades needs sophisticated equipment like hot-films or microphone arrays. Contrarily thermographic pictures can easily be taken from the ground and temperature differences indicate different states of the boundary layer. The accuracy however, still is an open question, so that an aerodynamic glove known from experimental research on aero-planes was used to classify the boundary-layer state of a 2 megawatt wind turbine blade operating in the orthern part of Schleswig-Holstein, Germany. State-of-the-art equipment for measurering static surface pressure was used for monitoring the lift distribution. To distinguish laminar and turbulent parts of the boundary layer (suction side only) 48 microphones were applied together with ground-based thermographic cameras from two teams. Additionally, an optical camera mounted on the hub was used to survey vibrations. During start-up (from 0 to 9 rpm) extended, but irregularly shaped regions of a laminar boundary layer were observed which had the same extension measured both with microphones and Thermography. When an approximately constant rotor rotation (9 rpm corresponding to approximately 6 m/s wind-speed) was achieved, a flow transition was visible at the expected position of 40 % chord length on the rotor blade, which was fouled with dense turbulent wedges and an almost complete turbulent state on the glove was detected. In all observations, quantitative determination of the flow transition positions from thermography and microphones agree well within their accuracy.

show abstract

Measurement uncertainty of IR thermographic flow visualization measurements for transition detection on wind turbines in operation

Cited by 38 publications

References 29 publications

Investigation of Laminar–Turbulent Transition on a Rotating Wind-Turbine Blade of Multimegawatt Class with Thermography and Microphone Array

Investigation of Laminar–Turbulent Transition on a Rotating Wind-Turbine Blade of Multimegawatt Class with Thermography and Microphone Array

Remote surface damage detection on rotor blades of operating wind turbines by means of infrared thermography

Investigation of Laminar-Turbulent Transition on a Rotating Wind Turbine Blade of Multi Megawatt Class with Thermography and a Microphone Array

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