Advanced infrared thermography data analysis for unsteady boundary layer transition detection

Mertens, Christoph; Wolf, Christian; Gardner, Anthony Donald; Schrijer, F.F.J.; Oudheusden, B.W. van

doi:10.1088/1361-6501/ab3ae2

Cited by 10 publications

(13 citation statements)

References 25 publications

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“…As discussed by Gardner et al (2017) for unsteady transition on a pitching airfoil, increasing the time difference (or angle difference here) between the infrared frames used to construct the DIT curve causes an erroneous drift from the true location of interest. The suggested approach is to minimize this difference while the DIT peaks still remain detectable (Mertens et al, 2020). This is indicated in Fig.…”

Section: Differential Infrared Thermographymentioning

confidence: 99%

Experimental Characterization of an Unsteady Laminar Separation Bubble on a Pitching Wing

Guerra

Mertens

Little

et al. 2022

Preprint

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The laminar separation bubble (LSB) that forms on the suction side of a modified NACA \(64_3-618\) airfoil at a chord-based Reynolds number of \(Re = 200,000\) is studied using wind tunnel experiments. First, the LSB is characterized over a range of static angles of attack, - in terms of the locations of separation, transition and reattachment - using surface pressure measurements, particle image velocimetry (PIV) and infrared thermography (IT). For the conditions tested, excellent agreement between the techniques is obtained, showing an upstream shift of the bubble with increasing angle of attack. For the study of steady LSBs, the infrared approach is found to be superior, in view of its higher spatial resolution and experimental simplicity. Subsequently, a pitching motion is imposed on the wind tunnel model, with reduced frequencies up to \(k = 0.25\). While surface pressure measurements and PIV are not affected by the change in experimental conditions, the infrared approach is seriously limited by the thermal response of the surface. To overcome this limitation, an extension of the recently proposed differential infrared thermography (DIT) method is considered. With this method, the unsteady behaviour of the LSB can be partially detected. All three experimental techniques indicate a hysteresis in bubble location between the pitch up and pitch down phases of the motion, caused by the effect of the aerodynamic unsteadiness on the adverse pressure gradient. However, the DIT measurements suggest a larger hysteresis, which is again attributed to the thermal response time of the model surface. The experimental results further reveal that the hysteresis in bubble location is larger than that of the circulation of the wing, indicating that the observed bubble hysteresis is not purely due to instantaneous flow conditions, but has an inherent component as well.

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Section: Differential Infrared Thermographymentioning

confidence: 99%

Experimental Characterization of an Unsteady Laminar Separation Bubble on a Pitching Wing

Guerra

Mertens

Little

et al. 2022

Preprint

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“…Various methods exist for detecting laminar-turbulent flow transitions in thermograms, yet most approaches explicitly ignore turbulence wedges. One such approach called 'local infrared thermography' is presented by Mertens et al [10] to detect unsteady transitions in periodic pitching processes. A pitching airfoil was investigated in a wind tunnel and thermograms were captured over multiple pitching periods.…”

Section: State Of the Artmentioning

confidence: 99%

Automated Detection of Premature Flow Transitions on Wind Turbine Blades Using Model-Based Algorithms

Parrey¹,

Gleichauf²,

Sorg³

et al. 2021

Applied Sciences

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Defects on rotor blade leading edges of wind turbines can lead to premature laminar–turbulent transitions, whereby the turbulent boundary layer flow forms turbulence wedges. The increased area of turbulent flow around the blade is of interest here, as it can have a negative effect on the energy production of the wind turbine. Infrared thermography is an established method to visualize the transition from laminar to turbulent flow, but the contrast-to-noise ratio (CNR) of the turbulence wedges is often too low to allow a reliable wedge detection with the existing image processing techniques. To facilitate a reliable detection, a model-based algorithm is presented that uses prior knowledge about the wedge-like shape of the premature flow transition. A verification of the algorithm with simulated thermograms and a validation with measured thermograms of a rotor blade from an operating wind turbine are performed. As a result, the proposed algorithm is able to detect turbulence wedges and to determine their area down to a CNR of 2. For turbulence wedges in a recorded thermogram on a wind turbine with CNR as low as 0.2, at least 80% of the area of the turbulence wedges is detected. Thus, the model-based algorithm is proven to be a powerful tool for the detection of turbulence wedges in thermograms of rotor blades of in-service wind turbines and for determining the resulting areas of the additional turbulent flow regions with a low measurement error.

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“…IR thermometry is also an optical measurement method of the temperature field, similar to TSP [ 2 , 3 , 4 , 5 , 6 , 7 , 8 ]. However, the measurement accuracy deteriorates in a cryogenic condition because the IR thermometry uses thermal radiation to measure the temperature.…”

Section: Introductionmentioning

confidence: 99%

Influence of Formulations on Characteristics of Ruthenium-Based Temperature-Sensitive Paints

Ikami

Fujita

Nagai

2022

Sensors

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Temperature-sensitive paint (TSP) can optically measure a global temperature distribution using a thermal quenching of dye molecules. The TSP measurement is often used in wind tunnel tests to measure the temperature and flow fields in the aerodynamic field. The measurement accuracy is affected by the characteristics of TSP, such as temperature sensitivity, pressure dependency, luminescent intensity, photostability, and surface condition. The characteristics depend on the formulation of TSP. This study investigates the characteristics of the TSP using dichlorotris (1,10-phenanthroline) ruthenium(II) hydrate (Ru-phen). We compare the characteristics of TSPs using different polymers, solvents, and dye concentrations. The TSPs using polyacrylic acid as a polymer shows linear calibration curves, high luminescent intensity, high photostability, and smooth surface. On the other hand, the TSPs using polymethyl methacrylate have nonlinear calibration curves, low luminescent intensity, strong photodegradation, and a rough surface.

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Advanced infrared thermography data analysis for unsteady boundary layer transition detection

Cited by 10 publications

References 25 publications

Experimental Characterization of an Unsteady Laminar Separation Bubble on a Pitching Wing

Experimental Characterization of an Unsteady Laminar Separation Bubble on a Pitching Wing

Automated Detection of Premature Flow Transitions on Wind Turbine Blades Using Model-Based Algorithms

Influence of Formulations on Characteristics of Ruthenium-Based Temperature-Sensitive Paints

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