Implementation of an In-Situ Infrared Calibration Method for Precise Heat Transfer Measurements on a Linear Cascade

Aberle, Svenja; Bitter, M.; Hoefler, Florian; Benignos, Jorge Carretero; Niehuis, Reinhard

doi:10.1115/1.4041132

Cited by 6 publications

(4 citation statements)

References 6 publications

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“…In contrast to thermocouples, however, IR cameras have to undergo a more extensive calibration to deliver accurate temperature readings. 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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“…It is known, that precise heat transfer coefficient (HTC) measurements using heated surfaces are challenging with respect to the precise distinction of the conductive, convective and radiative portions of the heat flux, compare e.g., [21][22][23]. The work of Estorf [24] emphasizes the calculation of the complex multi-lateral heat fluxes through a finite model in order to estimate high-accuracy heat fluxes from image-based temperature fields.…”

Section: Heat Transfer Coefficientmentioning

confidence: 99%

An Ultra-Fast TSP on a CNT Heating Layer for Unsteady Temperature and Heat Flux Measurements in Subsonic Flows

Bitter

Hilfer

Schubert

et al. 2022

Sensors

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In this paper, the authors demonstrate the application of a modified Ru(phen)-based temperature-sensitive paint which was originally developed for the evaluation of unsteady aero-thermodynamic phenomena in high Mach number but short duration experiments. In the present work, the modified TSP with a temperature sensitivity of up to −5.6%/K was applied in a low Mach number long-duration test case in a low-pressure environment. For the demonstration of the paint’s performance, a flat plate with a mounted cylinder was set up in the High-Speed Cascade Wind Tunnel (HGK). The test case was designed to generate vortex shedding frequencies up to 4300 Hz which were sampled using a high-speed camera at 40 kHz frame rate to resolve unsteady surface temperature fields for potential heat-transfer estimations. The experiments were carried out at reduced ambient pressure of p∞ = 13.8 kPa for three inflow Mach numbers being Ma∞=[0.3;0.5;0.7]. In order to enable the resolution of very low temperature fluctuations down to the noise floor of 10−5 K with high spatial and temporal resolution, the flat plate model was equipped with a sprayable carbon nanotube (CNT) heating layer. This constellation, together with the thermal sensors incorporated in the model, allowed for the calculation of a quasi-heat-transfer coefficient from the surface temperature fields. Besides the results of the experiments, the paper highlights the properties of the modified TSP as well as the methodology.

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“…Aberle-Kern et al [11] successfully proposed a methodology for loss determination downstream of cascades under consideration of thermal gradients in non-adiabatic flow fields by utilizing a newly developed combined thermal-and multi-hole probe. steady-state surface temperature sensing methodology for precise heat transfer estimations based on the Infrared Thermography is already available in the HGK, see Aberle et al [15].…”

Section: Available Measurement Techniquesmentioning

confidence: 99%

The High-Speed Cascade Wind Tunnel at the Bundeswehr University Munich after a Major Revision and Upgrade

Niehuis

Bitter

2021

IJTPP

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Since its first operation in 1956 at DFL Braunschweig and after its movement to Munich, the High-Speed Cascade Wind Tunnel (HGK) at Bundeswehr University Munich is intensively used for fundamental and application-oriented research on aero-thermodynamics of turbomachinery bladings. Numerous systematic airfoil design studies were performed over the last decades. Thanks to the HGK facility, which enables thorough and detailed cascade testing at turbomachinery-relevant conditions, many of those airfoils for different purposes finally made it into turbomachinery applications. Nowadays, the HGK still provides very useful contributions to the understanding of the complicated flow in compressor and turbine bladings, and thereby extends the knowledge on relevant physical phenomena. As a consequence of the intense usage, this unique test facility was subject to a major revision and upgrade. The performed changes are presented within this paper including an overview on new capabilities in terms of the extended operating range, the data acquisition system, and the recently available measurement equipment.

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Implementation of an In-Situ Infrared Calibration Method for Precise Heat Transfer Measurements on a Linear Cascade

Cited by 6 publications

References 6 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

An Ultra-Fast TSP on a CNT Heating Layer for Unsteady Temperature and Heat Flux Measurements in Subsonic Flows

The High-Speed Cascade Wind Tunnel at the Bundeswehr University Munich after a Major Revision and Upgrade

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