Infrared thermography for detection of laminar–turbulent transition in low-speed wind tunnel testing

Joseph, Liselle A.; Borgoltz, Aurélien; Devenport, William J.

doi:10.1007/s00348-016-2162-4

Cited by 45 publications

(33 citation statements)

References 17 publications

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“…Whereas initially only experiments under ultra-and hypersonic conditions were thermographically accompanied, over time measurements in transonic and subsonic flows were also established [25]. Typical applications in wind-tunnel experiments are the localization of the laminar-turbulent transition and the identification of laminar or turbulent flow separations [26,27]. In addition, the measurement method was transferred to the free field to localize the laminar-turbulent transition on aircraft wings [28] and helicopter rotors [29] for flight tests under real conditions.…”

Section: Thermographymentioning

confidence: 99%

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%

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 general, aluminum is not considered to be suitable for IRT applications because of high thermal conductivity blurring any thermal contrast by internal heat equalization (Tropea et al, 2007). To overcome this problem, the airfoil is covered with a matte black PVC foil (thickness < 100 µm) which inhibits the thermal conduction transversally to the surface while the geometry is negligibly changed (Reyer et al, 2006;Joseph et al, 2016). Such a configuration provides sharp thermal imaging with sufficient heat capacity to maintain temperature differences that emerge due to flow characteristics.…”

Section: Wind Tunnel Measurements Of Turbulent Wedges On Airfoilsmentioning

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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“…While the inflow turbulence intensity for an airplane wing in cruise is lower than the one experienced in a wind tunnel, it is higher for a rotating machinery or wind turbine rotors (Hernandez et al, 2012). Transition analysis performed for wind tunnel experiments in controlled conditions includes measurements on wind turbine airfoils equipped with pressure taps and sensors, balance system and a wake rake (Ceyhan et al, 2017); infrared thermography (Joseph et al, 2016); rotating turbine blade equipped with pressure sensors, strain gauges, balance system and particle image velocimetry (Schepers and Snel, 2007), rotating wind turbine and wind turbine blade experiments by oil visualization, stethoscope and flush-mounted unsteady pressure sensors (Lobo et al, 2018), wind turbine airfoil with pressure sensors and high frequency microphones (Özçakmak et al, 2019).…”

Section: Introductionmentioning

confidence: 99%

Laminar-turbulent transition characteristics of a 3-D wind turbine rotor blade based on experiments and computations

Özçakmak¹,

Madsen²,

Sørensen³

et al. 2020

Preprint

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Abstract. Laminar-turbulent transition behaviour of a wind turbine blade section is investigated in this study by means of field experiments and 3-D computational fluid dynamics (CFD) rotor simulations. The power spectral density (PSD) integrals of the pressure fluctuations obtained from the high frequency microphones mounted on a blade section are analyzed to detect laminar-turbulent transition locations from the experiments. The atmospheric boundary layer (ABL) velocities and the turbulence intensities (T.I.) measured from the field experiments are used to create several inflow scenarios for the CFD simulations. Results from the natural and the bypass transition models of the in-house CFD EllipSys code are compared with the experiments. It is seen that the bypass transition model results fit well with experiments at the azimuthal positions where the turbine is under wake and high turbulence, while the results from other cases show agreement with the natural transition model. Furthermore, the influence of inflow turbulence, wake of an upstream turbine and angle of attack (AOA) on the transition behaviour is investigated through the field experiments. On the pressure side of the blade section, at high AOA values and wake conditions, variation of the transition location covers up to 44 % of the chord during one revolution, while for the no wake cases and lower AOA values, variation occurs along a region that covers only 5 % of the chord. The effect of the inflow turbulence on the effective angle of attack as well as its direct effect on transition is observed. Transition locations for the wind tunnel conditions and field experiments are compared together with 2D and 3D CFD simulations. In contrast to the suction side, significant difference in the transition locations is observed between wind tunnel and field experiments on the pressure side for the same airfoil geometry. It is seen that the natural and bypass transition models of EllipSys3D can be used for transition prediction of a wind turbine blade section for high Reynolds number flows by applying various inflow scenarios separately to cover the whole range of atmospheric occurrences.

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Infrared thermography for detection of laminar–turbulent transition in low-speed wind tunnel testing

Cited by 45 publications

References 17 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

Laminar-turbulent transition characteristics of a 3-D wind turbine rotor blade based on experiments and computations

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