A spatially resolved in situ calibration applied to infrared thermography

Elfner, Maximilian; Glasenapp, Tobias; Schulz, Achmed; Bauer, Hans‐Jörg

doi:10.1088/1361-6501/ab1db5

Cited by 11 publications

(3 citation statements)

References 29 publications

(39 reference statements)

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“…Martiny et al [15] present an in-situ calibration for infrared thermography with thermocouples embedded in the surface of interest; a setup later improved for highly curved surfaces by Aberle et al [16]. Considering non-uniform background radiation reflected by the surface, Elfner et al [17] developed a spatially resolved calibration based on ray-tracing algorithms.…”

Section: State Of the Artmentioning

confidence: 99%

Heat transfer and film cooling measurements on aerodynamic geometries relevant for turbomachinery

et al. 2021

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A measurement technique for recording convective heat transfer coefficient and adiabatic film cooling effectiveness in demanding environments with highly curved surfaces and limited optical access, such as turbomachinery, is presented. Thermography and tailor-made flexible heating foils are used in conjunction with a novel multistep calibration and data reduction method. This method compensates for sensor drift, angle dependence of surface emissivity and window transmissivity, heat flux inhomogeneity, and conductive losses. The 2D infrared images are mapped onto the 3D curved surfaces and overlapped, creating surface maps of heat transfer coefficient and film cooling effectiveness covering areas significantly larger than the window size. The measurement technique’s capability is demonstrated in a sector-cascade test rig of a turbine center frame (TCF), an inherent component of modern two-spool turbofan engines. The horseshoe vortices were found to play a major role for the thermal integrity of turbine center frames, as they lead to a local increase in heat transfer, and at the same instance, to a reduction of film cooling effectiveness. It was also found that the horseshoe vortices lift off from the curved surface at 50% hub length, resulting in a pair of counter-rotating vortices. The measurement technique was validated by comparing the data against flat plate correlations and also by the linear relation between temperature difference and heat flux. This study is complemented with an extensive error and uncertainty analysis. Article highlights This paper presents an accurate measurement technique for heat transfer and film cooling on 3D curved surfaces with limited optical access using flexible tailor-made heating foils, infrared thermography and a high-fidelity multistep calibration process. Graphical abstract

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Section: State Of the Artmentioning

confidence: 99%

Heat transfer and film cooling measurements on aerodynamic geometries relevant for turbomachinery

et al. 2021

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“…; Colbert 2006). Use of thermocouples (Martiny et al 1996) or ray-tracing methods (Elfner et al 2019) has aided this endeavor. However, additional theoretical and experimental data are necessary to develop accurate numerical simulations to measure the difference in temperature between a surface target and ground surface (Schachne et al 1998).…”

Section: Surface Objectsmentioning

confidence: 99%

Buried-object-detection improvements incorporating environmental phenomenology into signature physics

Clausen¹,

Truong²,

Bragdon³

et al. 2022

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The ability to detect buried objects is critical for the Army. Therefore, this report summarizes the fourth year of an ongoing study to assess environ-mental phenomenological conditions affecting probability of detection and false alarm rates for buried-object detection using thermal infrared sensors. This study used several different approaches to identify the predominant environmental variables affecting object detection: (1) multilevel statistical modeling, (2) direct image analysis, (3) physics-based thermal modeling, and (4) application of machine learning (ML) techniques. In addition, this study developed an approach using a Canny edge methodology to identify regions of interest potentially harboring a target object. Finally, an ML method was developed to improve automatic target detection and recognition performance by accounting for environmental phenomenological conditions, improving performance by 50% over standard automatic target detection and recognition software.

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“…This causes a temperature uncertainty of ±0.3 K. Performing an in situ calibration would drastically reduce the uncertainty and at the same time account for variations in transmissivity and emissivity. Elfner et al managed to reduce the uncertainty by a factor of four through their in situ calibration [24]. Surface RTDs were installed on the two cooled blades, with the hope of providing an in situ measurement source, but it was not possible to place them in a location with an acceptable view angle for accurate calibration.…”

Section: Uncertainty Identificationmentioning

confidence: 99%

Infrared Temperature Measurements of the Blade Tip for a Turbine Operating at Corrected Engine Conditions

Christensen

Celestina

Sperling

et al. 2021

Journal of Turbomachinery

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A high-speed infrared camera is used to measure the temperature of blade tips in a cooled high-pressure turbine operating at corrected engine conditions in The Ohio State University Turbine Test Facility. These experiments create a challenging problem for infrared imaging since the rotor turns at over 13,000 rpm with tip speeds on the order of 300 m/s, and the surface temperature of the airfoils is on the order of 350 K. This means that the camera needs to capture a low intensity signal in a short time period. This paper will review the design and operation of a measurement procedure to accomplish this difficult task along with the post-processing steps necessary to extract useful data. Raw infrared images are processed by deblurring the images using a non-blind Wiener filter and mapping the two-dimensional data onto the three-dimensional blade. This paper also describes experiments covering a range of cooling flow rates and main flow temperatures. In addition, several tests with no main flow and only cooling flow were performed at lower speeds to reduce motion blur and enable the separation of internal and external heat transfer information. Results show that the infrared data is consistent and can provide quantitative comparisons of cooling performance even at the high rotation speed. This paper presents the lessons learned for high-speed infrared measurement along with representative data to illustrate the repeatability and capability of the measurement scheme as well as suggested improvements to guide further development.

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A spatially resolved in situ calibration applied to infrared thermography

Cited by 11 publications

References 29 publications

Heat transfer and film cooling measurements on aerodynamic geometries relevant for turbomachinery

Heat transfer and film cooling measurements on aerodynamic geometries relevant for turbomachinery

Buried-object-detection improvements incorporating environmental phenomenology into signature physics

Infrared Temperature Measurements of the Blade Tip for a Turbine Operating at Corrected Engine Conditions

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