Scheimpflug Self-Calibration Based on Tangency Points

International audienceSPIV self-calibration strongly depends on the accuracy of the detection of the projection of the control points. A new family of control points and an algorithm of image detection are proposed to overcome the bias associated to the use of dot centers as control points in SPIV self-calibration

Review of Calibration Methods for Scheimpflug Camera

The Scheimpflug camera offers a wide range of applications in the field of typical close-range photogrammetry, particle image velocity, and digital image correlation due to the fact that the depth-of-view of Scheimpflug camera can be greatly extended according to the Scheimpflug condition. Yet, the conventional calibration methods are not applicable in this case because the assumptions used by classical calibration methodologies are not valid anymore for cameras undergoing Scheimpflug condition. Therefore, various methods have been investigated to solve the problem over the last few years. However, no comprehensive review exists that provides an insight into recent calibration methods of Scheimpflug cameras. This paper presents a survey of recent calibration methods of Scheimpflug cameras with perspective lens, including the general nonparametric imaging model, and analyzes in detail the advantages and drawbacks of the mainstream calibration models with respect to each other. Real data experiments including calibrations, reconstructions, and measurements are performed to assess the performance of the models. The results reveal that the accuracies of the RMM, PLVM, PCIM, and GNIM are basically equal, while the accuracy of GNIM is slightly lower compared with the other three parametric models. Moreover, the experimental results reveal that the parameters of the tangential distortion are likely coupled with the tilt angle of the sensor in Scheimpflug calibration models. The work of this paper lays the foundation of further research of Scheimpflug cameras

Aerothermal Analysis of Film Cooling Flows

Flow field and thermal film cooling parameters are analysed and compared for different blowing ratios for a 10°-10°-10° laidback fan-shaped film cooling hole geometry with an inclination angle of 35° and a wide spacing of P/D = 8 to ensure the absence of jet interaction. The influence of the coolant ejection on the aerodynamics of the hot gas is investigated and stationary as well as non-stationary vortex structures are identified. The present study uses an existing test rig at the Institute of Thermal Turbomachinery (ITS) at the Karlsruhe Institute of Technology (KIT) designed for generic film cooling studies with high spatial resolution applying stereoscopic particle image velocimetry (SPIV) as well as infrared thermography (IRT). Operating conditions of hot gas and cooling air inlet and exit are uniquely compliant with scaled engine-realistic conditions, including temperature ratio, turbulence intensity and coolant flow configuration

Defocusing digital particle image velocimetry and the three-dimensional characterization of two-phase flows

Defocusing digital particle image velocimetry (DDPIV) is the natural extension of planar PIV techniques to the third spatial dimension. In this paper we give details of the defocusing optical concept by which scalar and vector information can be retrieved within large volumes. The optical model and computational procedures are presented with the specific purpose of mapping the number density, the size distribution, the associated local void fraction and the velocity of bubbles or particles in two-phase flows. Every particle or bubble is characterized in terms of size and of spatial coordinates, used to compute a true three-component velocity field by spatial three-dimensional cross-correlation. The spatial resolution and uncertainty limits are established through numerical simulations. The performance of the DDPIV technique is established in terms of number density and void fraction. Finally, the velocity evaluation methodology, using the spatial cross-correlation technique, is described and discussed in terms of velocity accuracy

The Application of Stereoscopic PIV in a Liquid-fueled Gas Turbine Combustor

Strict regulations on aviation gas turbine engine emissions and fuel consumptio

Multi-Aperture Fourier Ptychographic Microscopy: development of a high-speed gigapixel coherent computational microscope

Medical research and clinical diagnostics require imaging of large sample areas with sub-cellular resolution. Conventional imaging techniques can provide either high-resolution or wide field-of-view (FoV) but not both. This compromise is conventionally defeated by using a high NA objective with a small FoV and then mechanically scan the sample in order to acquire separate images of its different regions. By stitching these images together, a larger effective FoV is then obtained. This procedure, however, requires precise and expensive scanning stages and prolongs the acquisition time, thus rendering the observation of fast processes/phenomena impossible. A novel imaging configuration termed Multi-Aperture Fourier Ptychographic Microscopy (MA-FPM) is proposed here based on Fourier ptychography (FP), a technique to achieve wide-FoV and high-resolution using time-sequential synthesis of a high-NA coherent illumination. MA-FPM configuration utilises an array of objective lenses coupled with detectors to increase the bandwidth of the object spatial-frequencies captured in a single snapshot. This provides high-speed data-acquisition with wide FoV, high-resolution, long working distance and extended depth-of-field. In this work, a new reconstruction method based on Fresnel diffraction forward model was developed to extend FP reconstruction to the proposed MA-FPM technique. MA-FPM was validated experimentally by synthesis of a 3x3 lens array system from a translating objective-detector system. Additionally, a calibration procedure was also developed to register dissimilar images from multiple cameras and successfully implemented on the experimental data. A nine-fold improvement in captured data-bandwidth was demonstrated. Another experimental configuration was proposed using the Scheimpflug condition to correct for the aberrations present in the off-axis imaging systems. An experimental setup was built for this new configuration using 3D printed parts to minimise the cost. The design of this setup is discussed along with robustness analysis of the low-cost detectors used in this setup. A reconstruction model for the Scheimpflug configuration FP was developed and applied to the experimental data. Preliminary experimental results were found to be in agreement with this reconstruction model. Some artefacts were observed in these results due to the calibration errors in the experiment. These can be corrected by using the self-calibration algorithm proposed in the literature, which is left as a future work. Extensions to this work can include implementing multiplexed illumination for further increasing the data acquisition speed and diffraction tomography for imaging thick samples

PlenoptiCam v1.0: A light-field imaging framework

This is an accepted manuscript of an article published by IEEE in IEEE Transactions on Image Processing on 19/07/2021. Available online: https://doi.org/10.1109/TIP.2021.3095671 The accepted version of the publication may differ from the final published version.Light-field cameras play a vital role for rich 3-D information retrieval in narrow range depth sensing applications. The key obstacle in composing light-fields from exposures taken by a plenoptic camera is to computationally calibrate, re-align and rearrange four-dimensional image data. Several attempts have been proposed to enhance the overall image quality by tailoring pipelines dedicated to particular plenoptic cameras and improving the color consistency across viewpoints at the expense of high computational loads. The framework presented herein advances prior outcomes thanks to its cost-effective color equalization from parallax-invariant probability distribution transfers and a novel micro image scale-space analysis for generic camera calibration independent of the lens specifications. Our framework compensates for artifacts from the sensor and micro lens grid in an innovative way to enable superior quality in sub-aperture image extraction, computational refocusing and Scheimpflug rendering with sub-sampling capabilities. Benchmark comparisons using established image metrics suggest that our proposed pipeline outperforms state-of-the-art tool chains in the majority of cases. The algorithms described in this paper are released under an open-source license, offer cross-platform compatibility with few dependencies and a graphical user interface. This makes the reproduction of results and experimentation with plenoptic camera technology convenient for peer researchers, developers, photographers, data scientists and others working in this field

Análise da qualidade de medidas F-PIV 2D-2C e 2D-3C da velocidade da fase líquida em uma coluna de bolhas

Orientadores: Sávio Souza Venâncio Vianna, Guilherme José de CastilhoTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia QuímicaResumo: A análise da fluidodinâmica em reatores de coluna de bolha é importante na compreensão dos mecanismos relacionados à transferência de calor, transferência de massa e taxa de reação química. A precisão das medições experimentais depende diretamente do domínio de medição. A Velocimetria por imagem de partículas (PIV) é uma técnica não intrusiva utilizada para determinar o campo de velocidade 2D ou 3D. Um campo 2D-3C (bidimensional, três componentes) pode ser determinado por duas câmaras com projeções diferentes numa disposição estereoscópica (PIV 2D-3C). A perda de correlação devido ao movimento fora do plano de pares de imagens de partículas, que é comum em aplicações PIV, pode ser reduzida usando o sistema PIV 2D-3C. Um problema encontrado nas aplicações 2D-3C PIV está relacionado com o acesso óptico em algumas instalações. Para determinar a velocidade da fase líquida, não é interessante registrar as bolhas no escoamento multifásico. Por conseguinte, as partículas traçadoras fluorescentes combinadas com um filtro passa-alta na câmara são utilizadas nos sistemas Fluorescent PIV (F-PIV). Este trabalho tem como objetivo avaliar a qualidade das medidas 2D-2C e 2D-3C F-PIV da velocidade da fase líquida no regime de escoamento homogêneo e de transição homogêneo-heterogêneo de uma seção de coluna de bolha. As imagens 2D-2C e 2D-3C F-PIV foram processadas utilizando standard cross-correlation (SCC), ensemble correlation (EC) e sliding-average correlation (SAC) para comparar a qualidade das medições. O coeficiente de correlação cruzada, a relação sinal-ruído (SNR) e a quantificação de incerteza PIV estimada por estatísticas de correlação foram utilizados como indicadores de qualidade. A baixa concentração de imagem de partícula (baixa ppp) e a baixa faixa dinâmica de velocidade (baixa DVR) foram identificadas como fontes de ruído dominante nas medidas PIV. O efeito do baixo ppp foi relacionado diretamente com o comportamento dos indicadores de qualidade baseados na conectividade de vizinhança espacial, erro de reconstrução 3C e no diâmetro do pico de correlação. Quanto às condições de qualidade da abordagem SCC, foram obtidos cinco limites que garantem que os outliers (falsos vetores) podem ser corrigidos sem que o campo vetorial perca a representatividade do escoamento. No regime de escoamento homogêneo, os ruídos randômicos causados pela baixa ppp foram consideravelmente reduzidos utilizando a abordagem SACAbstract: The fluid dynamics analysis in bubble column reactors is important in understanding the mechanisms related to heat transfer, mass transfer and chemical reaction rate. The accuracy of the experimental measurements depends directly on the measurement domain. Particle image velocimetry (PIV) is a non-intrusive technique used to determine the 2D or 3D velocity field. A 2D-3C (two dimensional, three-component) field can be determined by two cameras with different projections in a stereoscopic arrangement (2D-3C PIV). The loss of correlation due to the out-of-plane motion of pairs of particle images, which is common in PIV applications, can be reduced using the 2D-3C PIV system. A problem encountered in 2D-3C PIV applications is related to optical access in some facilities. In order to determine the liquid phase velocity, it is not interesting to record bubbles in the multiphase flow. Therefore, fluorescent tracer particles combined with a high-pass filter on the camera are used in the Fluorescent PIV (F-PIV) systems. This work aims to evaluate the quality of the 2D-2C and 2D-3C F-PIV measurements of the liquid phase velocity in the homogeneous and homogeneous-heterogeneous transition flow regime of a bubble column. The 2D-2C and 2D-3C F-PIV images were processed using standard cross-correlation (SCC), ensemble correlation (EC), and sliding-average correlation (SAC) to compare the measurements quality. The cross-correlation coefficient, signal-to-noise ratio (SNR) and PIV uncertainty estimated by correlation statistics were used as quality indicators. The low particle image concentration (low ppp) and low dynamic velocity range (low DVR) were identified as dominant noise sources in the PIV measurements. The effect of the low ppp was directly related to the behavior of the quality indicators based on the spatial neighborhood connectivity, 3C reconstruction error, and correlation peak diameter. Regarding the quality conditions for SCC approach, five limits were obtained that guarantee that the outliers can be corrected without the vector field losing the representativeness of the flow. In the homogeneous flow regime, the random noise caused by low ppp was considerably reduced using the SAC approachDoutoradoEngenharia QuímicaDoutor em Engenharia Química2296/2013CAPE

Tomographic shadowgraphy of swirled non-reactive spray injection in a generic aero engine burner under realistic operating conditions

This contribution describes the application of tomographic shadowgraphy to measure instantaneous velocities of droplets undergoing airblast-atomization in the non-reactive flow of a generic aero engine burner model at Weber numbers of Weaero = 36

Traversing SPIV for the measurement of vortex rings under background rotation

This thesis describes the statistical measurement of vortex ring velocity elds. The measurements were conducted using high accuracy SPIV, with the measurement system traversing with the vortex ring. This incurred two sources of error: vibration led to the superposition of a fluctuating bias across the entire velocity frame; motion of the cameras over time gave rise to inaccuracies in the camera calibration, thus a registration error. Furthermore vortex rings' trajectories carried them away from the centre of the light sheet. The development, implementation and basic evaluation of the corrections to the velocity eld to account for these problems (which showed an overall improvement) was a significant undertaking and constitutes a major portion of the work. The vortex ring measurements were performed on the University of Warwick's recently commissioned unique, large scale, geophysical vortex facility. This enabled measurement of the vortex rings inside a rotating environment and the effects of Coriolis force upon discrete vortex structures to be investigated. Through consideration of the mean velocity elds for non-rotating vortex rings and the properties derived thereof (trajectory, diameter, circulation, core diameter), several flow phenomena are discussed: the axial swirling flow seen by Naitoh et al. (2002) is shown to vary across a wide range of values and tentative support presented for the existence of differing classes of turbulent vortex rings (Dziedzic and Leutheusser, 2004). Analysis of similar properties for vortex rings produced under background rotation, as well as reinterpretation of numerical results presented by Verzicco et al. (1996) (the single prior work on the subject), leads to a detailed description of the dynamics of the velocity eld evolution. In addition, it is shown that nondimensionalising time evolution curves of vortex ring trajectory and circulation cause data collapse across a range of generation conditions and rotation rates