Benjamin Leclaire

• Ecole Polytechnique, PhD
• Researcher at Office National d'Études et de Recherches Aérospatiales

Within the framework of the European Union Horizon 2020 project HOMER (Holistic Optical Metrology for Aero-Elastic Research), data assimilation (DA) algorithms for dense flow field reconstructions developed by different research teams, hereafter referred to as the participants, were comparatively assessed. The assessment is performed using a synthe...

Within the framework of the European Union’s Horizon 2020 project HOMER (Holistic Optical Metrology for Aero-Elastic Research), data assimilation (DA) algorithms for dense flow fields reconstructions are comparatively assessed. The assessment is performed using a synthetic database that reproduces the turbulent flow in the wake of a cylinder in wal...

Following the successful first edition of the Lagrangian Particle Tracking (LPT) and Data Assimilation (DA) challenges organized in 2020, new LPT and DA challenges are being prepared, whose results will be presented between the ISFV21 and ISPIV16 conferences in Tokyo, Japan, in June 2025. Interested to know more? Scan the QR code on the left in t...

This talk gives an overview of the advances in 2022 within the CUBE2 Common reasearch project. Main topics are an Onera-developed data assimilation method for interpolation of two-pulse partice tracking data and the first results of the 3D Lagrangian Particle Tracking experiment of transiational flow behind a 2D step and a small cube-shape obstacle...

In this study, a reconstruction procedure to infer full 3D instantaneous velocity and pressure fields from sparse velocity measurements is proposed, here focusing on the case of scattered data as provided by Particle Tracking Velocimetry (PTV). A key characteristic of the present approach is that it only relies on single-instant velocity measuremen...

In this work, we extend the analysis of Lagrangian Particle Tracking (LPT) and Data Assimilation (DA) algorithms, presented at the ISPIV21 conference, to the case of a turbulent wall-bounded flow interacting with a moving panel. The work is conducted within the European project HOMER and the data is processed by the partners of the project consorti...

In this work, we extend the analysis of Lagrangian Particle Tracking (LPT) and Data Assimilation (DA) algorithms, presented at the ISPIV21 conference, to the case of a turbulent wall-bounded flow interacting with a moving panel. The work is conducted within the European project HOMER and the data is processed by the partners of the project consorti...

We introduce a web portal dedicated to benchmarking Lagrangian Particle Tracking (LPT) and Data Assimilation (DA) processing algorithms. LPT is here understood in a wide sense, as we consider acquisition situations ranging from only two illuminations (i.e. Particle Tracking Velocimetry - PTV) to a large number of images. The website, https://www.on...

We investigate the estimation of the turbulent flow around a canonical square cylinder at $Re=22\,000$ based on temporally resolved but spatially sparse velocity data and solving the unsteady Reynolds-averaged Navier–Stokes (URANS) equations. Flow reconstruction from sparse data is achieved through the application of a nudging data assimilation tec...

This communication is intended to provide an overview of the numerical benchmark activities within HOMER, as well as their dissemination perspectives. Datasets all involve a turbulent wall-bounded flow, with spatio-temporal scales reflecting the complexity of flows of interest in aerodynamic and aeroelastic research. The wake flow of a cylinder of...

Following the First Challenge on Lagrangian Particle Tracking (LPT) and Data Assimilation (DA), organized in 2020 (see http://cfdforpiv.dlr.de/ and Leclaire et al.), the next numerical benchmark activities within the HOMER project take as their objectives to assess LPT and DA algorithms in a fluid-structure interaction situation. The physical situa...

This work presents the main results of the first Lagrangian Particle Tracking challenge, conducted within the framework of the European Union’s Horizon 2020 project HOMER (Holistic Optical Metrology for Aero-Elastic Research), grant agreement number 769237. The challenge, jointly organised by the research groups of DLR, ONERA and TU Delft, consider...

This paper aims at analysing the behaviour of particle localisation error in 3D Lagrangian Particle Tracking (LPT) techniques, with a particular emphasis on general properties, independent of a specific algorithm. Based on the hypothesis that in LPT algorithms, errors on the image formation models are solely due to random noise, we show/prove the e...

In the last decade, Lagrangian Particle Tracking (LPT) has emerged as one of the leading measurement techniques for the quantitative determination of fluid flows in three-dimensional domains (see e.g. Schanz et al., 2016), due to its accuracy in reconstructing particles velocities and material accelerations. Due to the scattered nature of the obtai...

This work presents the main results of the first Data Assimilation (DA) challenge, conducted within the framework of the European Union’s Horizon 2020 project HOMER (Holistic Optical Metrology for Aero-Elastic Research), grant agreement number 769237. The challenge was jointly organised by the research groups of DLR, ONERA and TU Delft. The same sy...

This paper aims at analysing the behaviour of particle localisation error in 3D Lagrangian Particle Tracking (LPT) techniques, with a particular emphasis on general properties, independent of a specific algorithm. Based on the hypothesis that in LPT algorithms, errors on the image formation models are solely due to random noise, we show/prove the e...

In the last decade, Lagrangian Particle Tracking (LPT) has emerged as one of the leading measurement techniques for the quantitative determination of fluid flows in three-dimensional domains (see e.g. Schanz et al., 2016), due to its accuracy in reconstructing particles velocities and material accelerations. Due to the scattered nature of the obtai...

This work presents the main results of the first Lagrangian Particle Tracking challenge, conducted within the framework of the European Union’s Horizon 2020 project HOMER (Holistic Optical Metrology for Aero-Elastic Research), grant agreement number 769237. The challenge, jointly organised by the research groups of DLR, ONERA and TU Delft, consider...

This work presents the main results of the first Lagrangian Particle Tracking challenge, conducted within the framework of the European Union’s Horizon 2020 project HOMER (Holistic Optical Metrology for Aero-Elastic Research), grant agreement number 769237. The challenge, jointly organised by the research groups of DLR, ONERA and TU Delft, consider...

In light of recent renewed interest in streaks in turbulent jets, the current work explores their coexistence with vortex rings in the near field of turbulent round jets. A Reynolds number, $Re=1.5 \times 10^5$ jet is studied at two diameters downstream of the nozzle, using high-speed stereo particle image velocimetry. The spectra of individual vel...

We perform an hybridation of high-fidelity (DNS) and low-fidelity (URANS) velocity fields of the turbulent wake behind a square cylinder at Reynolds number Re=22000. The nudging method is apllied to the URANS equations closed with the Spalart-Allamas model by adding in the momentum equations a feedback term measuring the discrepancy of the (URANS)...

A possible interaction between vortical structures in a round jet shear layer, viz. vortex rings and streamwise vortices, is explored following Davoust et al. (J. Fluid Mech., vol. 709, 2012, pp. 408–444). These authors reported a radial organization of streamwise vorticity in a jet at high diameter-based Reynolds number (Re), contrary to the class...

A novel method performing 3D PTV from double-frame multi-camera images is introduced. Particle velocities are estimated by following three steps: First, separate particle reconstructions with a sparsity based algorithm are performed on a fine grid. Second, they are expanded on a coarser grid on which 3D correlation is performed, yielding a predicto...

Streamwise vortices play an important role in the mixing and entrainment in the near field of jets. They are dynamically active structures that lead to additional flow features such as side jets and streaks. Their coexistence with and wrapping around the vortex rings suggest their possible influence on the rings as has been remarked in several stud...

Streamwise vortices play an important role in the mixing and entrainment in the near field of jets. They are dynamically active structures that lead to additional flow features such as side jets and streaks. Their coexistence with and wrapping around the vortex rings suggest their possible influence on the rings as has been remarked in several stud...

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 pred...

The dynamical significance of vortical structures in the near field of round jets, viz. the vortex rings and the stream-wise vortices, has been known for several decades. A fundamental understanding of their inter-actions, especially in turbulent jets at high Reynolds number (Re), is expected to provide an impetus to devising control strategies; fo...

The flow around a surface mounted cube with incoming turbulent boundary layer has been topic of many experimental and numerical investigations in the past decades. Despite its simple geometry the flow generates a set of complex vortical structures, includes flow separation at the three front plane edges with corresponding subsequent shear layer dyn...

This article presents a reconstruction of the unsteady behaviour of a round jet at a Reynolds number equal to 3300, from the sole knowledge of the time-averaged flow field and one pointwise unsteady measurement. The reconstruction approach is an application of the work of Beneddine et al. ( J. Fluid Mech. , vol. 798, 2016, pp. 485–504) and relies o...

Accurate simulation of industrial turbulent flows is still nowadays a challenge. The increase in computational capacities offer the ability to perform numerical simulations that resolve all flow scales (direct numerical simulations) for academic flow problems at moderate Reynolds numbers. However, for complex industrial flows at high Reynolds numbe...

We address calibration and self-calibration of tomographic PIV experiments within a pinhole model of cameras. A complete and explicit pinhole model of a camera equipped with a 2-tilt angles Scheimpflug adapter is presented. It is then used in a calibration procedure based on a freely moving calibration plate. While the resulting calibrations are ac...

We introduce a new method for estimating fluid trajectories in time-resolved PIV. It relies on a Lucas-Kanade paradigm and consists in a simple and direct extension of a two-frame estimation with FOLKI-PIV (Champagnat et al 2011 Exp. Fluids 50 1169-82). The so-called Lucas-Kanade Fluid Trajectories (LKFT) are assumed to be polynomial in time, and a...

Cette thèse porte sur le développement de la PIV tomographique pour la mesure d’écoulements turbulents. Elle se fonde sur la reconstruction tomographique d’une distribution volumique d’intensité de particules, à partir de projections enregistrées par des caméras. La principale difficulté est le bruit dit tomographique (particules fantômes) qui croî...

We present an analysis of variationnal data-assimilation with PIV measurements using a approach similar to [5] and implemented using FreeFEm++ [6]. We design synthetic PIV measurements build upon two references bidimensional configurations, the flow past a cylinder at Re = 125 and the forced flow downstream of a backward-facing step at Re = 800. Th...

The two time step Tomo-PTV technique recently introduced in [1], is compared with MLOS-SMART +3D correlation both in terms of reconstructions and velocity fields on synthetic dataset and on a cylindrical air jet experiment. We show that this new technique may be a reliable alternative to conventional Tomo-PIV to efficiently process experimental dat...

We introduce a new method for estimating fluid trajectories in time-resolved PIV. It relies on a Lucas-Kanade paradigm and consists in a simple and direct extension of a two-frame estimation proposed in that context [2]. The so-called Lucas-Kanade Fluid Trajectories (LKFT) are assumed to be polynomial in time, and are found as the minimizer of a gl...

Several particle image velocimetry experimental campaigns were carried out at the ONERA F1 wind tunnel with the aim of improving the understanding of the flow angularity in the test section. An innovative approach was implemented to enable using PIV for accurate clinometric measurements. Results were alidated against those acquired using the standa...

We propose an approach for efficient localization and intensity reconstruction of particles on a 3D grid based on sparsity principles. The computational complexity of the method is limited by using the Particle Volume Reconstruction paradigm (Champagnat et al., 2014), and a reduction of the problem dimension. Tests on synthetic and experimental dat...

We present an alternative approach to tomographic particle image velocimetry (tomo-PIV) that seeks to recover nearly single voxel particles rather than blobs of extended size. The baseline of our approach is a particle-based representation of image data. An appropriate discretization of this representation yields an original linear forward model wi...

The framework of this study is the conventional four cameras two time steps Tomo PIV. The rationale behind this paper, and its main contribution, is that using two ultra sparse tomographic reconstructions (one particle –one voxel: LocM-CoSaMP) at time step t and t+dt where the particles are only represented by the voxels they are embedded in, one c...

The near field of a 2.14 × 105 Reynolds number, low-Mach-number, cylindrical jet with and without swirl has been investigated by high-speed stereo PIV in a transverse plane, two diameters downstream of the jet exit. Using spatiotemporal correlations, we investigate the dynamics of streamwise vorticity in the shear layer, responsible for the mixing...

In this paper we present experimental factors affecting the quality of tomographic PIV reconstruction. Our main contribution is to introduce a new factor built on the geometrical considerations applied to the cameras field of views and the laser volume. By performing numerical tests, we show the influence of this parameter the reconstruction using...

The present study is aimed to analyse the effect of passive vortex generators in a transonic interaction between a shock-wave and a turbulent boundary layer in a channel flow at Mach number M = 1.45. Control of the boundary layer detachment downstream of the shock is obtained thanks to momentum transfer given by passive control devices, mechanical...

The near field of a Reynolds number and low-Mach-number cylindrical jet has been investigated by means of a high-speed stereo PIV setup that provides the spatio-temporal velocity field in a transverse plane, two diameters downstream of the jet exit. Proper orthogonal decomposition (POD) and spatio-temporal correlations are used to identify some of...

We investigate the generation conditions of a high-Reynolds-number swirling jet experiment, based on a rotating honeycomb device and using a final contraction. Using hot-wire measurements, we first show that for high swirl levels, the flow at the jet exhaust may exhibit fully developed turbulence in the whole plane. By analysing the fluctuation lev...

Our contribution deals with fast computation of dense two-component (2C) PIV vector fields using Graphics Processing Units (GPUs). We show that iterative gradient-based cross-correlation optimization is an accurate and efficient alternative to multi-pass processing with FFT-based cross-correlation. Density is meant here from the sampling point of v...

This paper theoretically investigates the influence of the upstream boundary conditions on the bifurcation structure leading to vortex breakdown. The axisymmetric flow of an inviscid fluid in a pipe of constant cross-section and finite axial length is considered. Solutions bifurcating from the columnar solution at criticality are analysed via a wea...

Past numerical studies on vortex breakdown in a duct have identified the choice of up- stream boundary conditions as a source of major concern. While the choice for axial and azimuthal velocity profiles is often dictated by the experiments, the choice for the third upstream condition does not appear unanimous and its influence on the scenario of tr...

Rusak and Meder [AIAA J. 42, 2284 (2004)] recently studied the behavior of a near-critical swirling flow in a weakly contracting duct. We investigate the particular inflow condition consisting of plug axial flow with solid body rotation, and introduce a new perturbation expansion specifically suited to that case. We show that the wall recirculation...

We study the mean dynamics of a radially confined, uniformly rotating flow of high Reynolds number. The duct geometry consists of a portion of constant cross-section followed by a final contraction, downstream of which the flow exhausts as a swirling jet. The duct flow is investigated by Stereoscopic PIV. To understand the specific effect of the co...

This thesis is a contribution to the study of rotating flow dynamics at high Reynolds number. It aims at explaining the destabilization, for a sufficiently high swirl number, of a uniformly rotating flow developing in a cylindrical duct of constant cross-section followed by a contraction, and exhausting as a swirling jet. The first part of the thes...

Cette thèse est une contribution à l'étude de la dynamique des écoulements tournants de grand nombre de Reynolds. Elle vise à expliquer la déstabilisation, à nombre de swirl élevé, d'un écoulement en rotation solide se développant dans une conduite cylindrique de section constante puis contractante, et débouchant en un jet. On caractérise d'abord l...

The generating conditions of a high-Reynolds swirling jet are addressed. The setup used involves a rotating honeycomb, followed by a transparent duct of constant cross-section and a final converging nozzle. Traditionaly, the contraction is expected to reduce turbulence in the exit plane, thereby leading to a smooth upstream condition for the subseq...

This article addresses the problem of the generation conditions of a high-Reynolds swirling jet, which to our knowledge has never been dealt with precisely in past experimental studies. We observe that the exit plane of a jet generated with a converging nozzle is progressively invaded by turbulence that is not related to the dynamics of the develop...

Nous proposons un nouveau paradigme pour la PIV Stéréo, reposant sur l'estimation directe du déplacement en utilisant simultanément les images des deux caméras. Ce déplacement est obtenu en minimisant un critère aux moindres carrés non linéaire faisant intervenir le déplacement d'une fenêtre d'interrogation. La minimisation est effectuée par l'appr...