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Optical Flow Velocimetry : optimization, benchmarking and application to system identification, modelling and control of shear flows

Abstract : An integrated and fruitful journey of an Optical Flow Velocimetry system in various fluid mechanics study cases is presented: From its development and benchmarking, to the application of its results in instability analysis, modelling, dynamics prediction and control of shear flows. Regarding development, the software (algorithm, Graphics User Interface) and hardware parts (camera, workstation, laser) part of the system are presented and discussed.Furthermore, the system is benchmarked on various experimental and synthetic fluidic datasets. We explore its spatial precision from simple step displacements test-cases, to synthetic homogeneous isotropic turbulence datasets and then grid-generated turbulence and finally a bluff body turbulent wake. After the advantages regarding spatial resolution and computational speed of the system comparing to other state-of-the-art velocimetry systemsare presented, a novel pressure reconstruction method is described and validated using the global turbulent kinetic energy budget in the turbulent wake of a D-shaped body, resolving scales down to the sub-Kolmogorov range. Then, Optical Flow measurements are used for modelling and system identification of two experimental datasets: On one hand the forced Turbulent Boundary Layer of a flat plate and on the other the Backward-Facing Step flow,for a maximum Reh = 3090. Modern data-driven methods are utilised for this purpose: a statistical learning approach and a Neural Network machine-learning approach. Last but not least, more light on the 3D instability of the Backward-Facing Step is shed as well, followedby a novel open-loop control strategy to reduce the volume of the recirculation bubble. Sucha full exploitation of a velocimetry system shares crucial insight on the importance of experimental,non intrusive methods such as Optical Flow Velocimetry, in the study of complexflows; flows that are often extremely costly or impossible to resolve numerically.
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Submitted on : Monday, October 4, 2021 - 4:24:28 PM
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  • HAL Id : tel-03364421, version 1

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Antonios Giannopoulos. Optical Flow Velocimetry : optimization, benchmarking and application to system identification, modelling and control of shear flows. Fluid mechanics [physics.class-ph]. Sorbonne Université, 2021. English. ⟨NNT : 2021SORUS097⟩. ⟨tel-03364421⟩

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