Double-frame tomographic PTV at high seeding densities - Archive ouverte HAL Access content directly
Journal Articles Experiments in Fluids Year : 2020

Double-frame tomographic PTV at high seeding densities

PTV tomographique à 2 pas de temps à hautes densités

Abstract

A novel method performing 3D PTV from double frame multi-camera images is introduced. Particle velocities are estimated by following three steps. Firstly, separate particle reconstructions with a sparsity-based algorithm are performed on a fine grid. Secondly, they are expanded on a coarser grid on which 3D correlation is performed, yielding a predictor displacement field that allows to efficiently match particles at the two time instants. As these particles are still located on a voxel grid, the third, final step achieves particle position refinement to their actual subvoxel position by a global optimization process, also accounting for their intensities. As it strongly leverages on principles from tomographic reconstruction, the technique is termed Double-Frame Tomo-PTV (DF-TPTV). Standard synthetic tests on a complex turbulent flow show that the method achieves high particle and vector detection efficiency, up to seeding densities of around 0.08 particles per pixel (ppp). On these tests, it also shows a higher robustness to noise and lower root-mean-square errors on velocity estimation than similar state-of-the-art methods. Results from an experimental campaign on a transitional round air jet at Reynolds number 4600 are also presented. Average seeding density varies in time from 0.06 to 0.03 ppp during the considered run, with different densities and signal-to-noise ratios being observed with time in the jet and ambient air regions, supplied by two different seeding systems. The strong polydisperse nature of the seeding, as well as the coexistence of two spatial zones of significantly different particle densities and signal-to-noise ratios, are observed to be the most influential sources of limitation for DF-TPTV performance. However, the method still successfully reconstruct a large amount of particles, and, associated to an outlier rejection scheme based on temporal statistics, truthfully reconstructs the instantaneous jet dynamics. Further quantitative performance assessment is then provided by introducing statistics performed by bin averaging, upon assuming statistical axisymmetry of the jet. Mean and fluctuating axial velocity components in the jet near-field are compared with reference results obtained from planar PIV at higher seeding density, with an interrogation window of size comparable to that of the bins. Results are found to be in excellent agreement with one another, confirming the high performance of DF-TPTV to yield reliable volumetric vector fields at seeding densities usually considered for tomographic PIV processing.,or even higher
Une nouvelle méthode permettant de faire de la PTV à deux pas de temps est présentée. La vélocimetrie des particules est estimée en trois étapes. Une reconstruction parcimonieuse sur une grille fine est faite pour chacun des 2 instants. Une corrélation 3D sur une grille grossière sert de prédicteur pour l'appariement temporel. Un processus d'optimisation global assure enfin une localisation précise hors grille des particules. Cette technique qui s'appuie fortement sur des principes de reconstruction tomographique est nommée DF-TPTV (Double Frame Tomographic PTV). Des tests synthétiques standards sur un écoulement turbulent montre qu'elle atteint de bonnes performances jusqu'à une ppp de 0.08. Ces tests montrent une meilleure robustesse au bruit et une rms des vitesses estimées inférieure à celle de méthode comparables de l'état de l'art. Les résultats de l'application de cette technique sur un jet transitionnel (Re=4600) sont présentés. La ppp de cette expérience décroît de 0.06 à 0.03 au cours de la séquence avec un ensemencement inhomogène et un rapport signal bruit très faible. Malgré ces facteurs de nuisance, DF-TPTV, associé à un schéma de réjection temporel simple permet l'obtention d'un nombre important de vecteurs d'un champ instantané qui restituent bien tout la dynamique du jet. Une comparaison portant sur des quantités statistiques est faite avec des résultats issus de traitements de PIV 2D et de PIV 3D tomographique.
Fichier principal
Vignette du fichier
DTIS20003.1592409144_postprint.pdf (8.93 Mo) Télécharger le fichier
Origin : Files produced by the author(s)
Loading...

Dates and versions

hal-02443793 , version 1 (17-01-2020)
hal-02443793 , version 2 (17-06-2020)

Identifiers

Cite

Philippe Cornic, Benjamin Leclaire, Frédéric Champagnat, Guy Le Besnerais, Adam Cheminet, et al.. Double-frame tomographic PTV at high seeding densities. Experiments in Fluids, 2020, 61 (2), ⟨10.1007/s00348-019-2859-2⟩. ⟨hal-02443793v2⟩

Altmetric

Share

Gmail Facebook X LinkedIn More