8,978 research outputs found
Measurement of surface temperature and emissivity with stereo dual-wavelength IR thermography
No full textThis work describes a temperature and emissivity measurement methodology that applies the multi-wavelength pyrometry principle to IR thermography using two IR cameras in a stereo arrangement with detectors working in different wavelength bands. The two radiation distributions measured by the IR cameras are rebuilt on the object surface mesh by means of the pinhole camera model and are used to write a system of equations in which
emissivities and temperatures are unknown quantities. By solving the system, the temperature and directional
emissivity of the material under test can be measured for each wavelength band. The influence on the proposed
methodology of the IR camera noise and of the temperature bias between the two cameras is numerically
analysed in the case of gray and non-gray bodies. To validate the proposed methodology, an experimental test
was performed on an object with known emissivity (measured in a conventional way)
Simultaneous measurement of temperature and emissivity with stereo dual band IR camera configuration
No full textThis work describes a temperature and emissivity measurement methodology that applies the multi-wavelength pyrometry principle to IR thermography using two dual band IR cameras in a stereo arrangement. The four radiation distributions measured by the IR cameras are rebuilt on the object surface mesh by means of the pinhole camera model and are used to write a system of equations in which emissivities and temperatures are unknown quantities. By solving the system, the temperature and directional emissivity of the material under test can be measured for each wavelength band
Temperature maps measurements on 3D surfaces with infrared thermography
No full textThe use of the infrared camera as a temperature
transducer in wind tunnel applications is convenient and
widespread. Nevertheless, the infrared data are available in
the form of 2D images while the observed surfaces are
often not planar and the reconstruction of temperature
maps over them is a critical task. In this work, after
recalling the principles of IR thermography, a methodology
to rebuild temperature maps on the surfaces of 3D object is
proposed. In particular, an optical calibration is applied to
the IR camera by means of a novel target plate with control
points. The proposed procedure takes also into account the
directional emissivity by estimating the viewing angle. All
the needed steps are described and analyzed. The advan-
tages given by the proposed method are shown with an
experiment in a hypersonic wind tunnel
Average and phase resolved heat transfer in single and twin circular synthetic impinging air jets
No full text
On the three-dimensional precessing jet flow past a sudden expansion
No full textA circular jet flow past an abrupt expansion under some conditions switches intermittently between two states: quasi-axisymmetric expansion and gyroscopic-like precessing motion. In this work, an experimental investigation into the self-excited precessing flow generated by a 5:1 expansion of a round jet in a coaxial cylindrical chamber is carried out by means of tomographic particle image velocimetry. The experiments are performed on a jet issued from a short pipe at a Reynolds number equal to 150,000. Proper orthogonal decomposition (POD) is applied to extract information on the organization of the large coherent structures of the precessing motion. The application of this technique highlights the dominance of three modes: the most energetic two are associated with the jet precession; the third one is representative of the axial motion. An estimate of the precession probability based on the modal energy obtained from the application of POD is proposed. The precession frequency is extracted using a low-order reconstruction (LOR) of a subset of the POD modes. The reconstructed flow field topology obtained by the LOR highlights an underlying mechanism of swirl generation in proximity of the inlet nozzle; the phenomenon is closely related to the interaction between the entrainment in the far field and the recirculation regions in the near field. The application of a stability criterion shows that the self-induced swirl flow results to be unstable. The instability is responsible for the generation of helicalshaped vortices in the near field, even though the dominant feature for the unconfined jet issued from the same nozzle is the axisymmetric ring-vortices generation
Time and phase average heat transfer in single and twin circular synthetic impinging air jets
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