Bio: Ludovic Chatellier is an academic researcher from University of Poitiers. The author has contributed to research in topics: Particle image velocimetry & Vortex shedding. The author has an hindex of 13, co-authored 48 publications receiving 535 citations. Previous affiliations of Ludovic Chatellier include Centre national de la recherche scientifique & Trinity College, Dublin.
Papers published on a yearly basis
TL;DR: In this paper, a linearized stability analysis for low Mach number turbulent flows is proposed in which the interface of the cavity is modeled by a vorticity layer, and the cavity flow is investigated experimentally in a subsonic wind tunnel, using pressure measurements and a phase-locked particle image velocimetry system.
Abstract: Theoretical and experimental investigations are conducted for rectangular cavities of varying sizes in low Mach number turbulent flows. Emphasis is put on the characterization of the generation of self-sustained oscillations in order to develop methods of active control applied to the aeroacoustics of cavity flows. A linearized stability analysis for low Mach number flows is proposed in which the interface of the cavity is modeled by a vorticity layer. Subsequently, the cavity flow is investigated experimentally in a subsonic wind tunnel, using pressure measurements and a phase-locked particle image velocimetry system. Experimental results indicate that the oscillation process is governed by convective waves, with no definite influence of convected vortical structures. The good agreement between the experimental data and the predictions given by the model allows the identification of the oscillations of the cavity interface via the parameters issued from the theoretical analysis.
TL;DR: In this article, an optical method for the measurement of the surface topography, height and normal, and the velocity in free surface flows is presented, based on the analysis of the apparent displacement between a reference and refracted images of a laser sheet through an interface viewed from two viewpoints.
Abstract: An optical method for the measurement of the surface topography, height and normal, and the velocity in free surface flows is presented. This method of surface reconstruction is based on the analysis of the apparent displacement between a reference and refracted images of a laser sheet through an interface viewed from two viewpoints. First, the validation of the method is performed in a wave tank by comparison with resistive wave probe measurements. This technique is then applied in a towing tank to measure the flow in the wake of a ship model. The results highlight correspondences between the free surface shape and the 2D velocity field beneath surface in the wake of the ship model. The instantaneous measurement of free surface allows a reconstruction of the global wave field pattern behind the ship. These results, obtained with a non-intrusive technique and with a high spatial resolution, allow an accurate analysis of the flow behind the ship. Tests were conducted for different Froude numbers in a range between 0.24 and 0.52. The results highlight the effect of the Froude number on established waves system.
TL;DR: In this article, experimental results for fish-friendly trashracks placed in an open water channel are presented. Butler et al. proposed a new head-loss equation that takes into account the effect of different tested parameters.
Abstract: Experimental results for fish-friendly trashracks placed in an open water channel are presented. Model trashracks with different bar shapes, spacing and angles were tested. The numerous configurations provided results on head losses and on changes in velocity along the rack for a large range of situations, including fish-friendly trashracks. Previous head-loss equations found in the literature were applied to these configurations and were compared with measurements. A new head-loss equation is proposed that takes into account the effect of the different tested parameters. Velocity measurements provided new results and answers concerning downstream-migration aspects such as admissible approach velocities and guidance efficiency as a function of the trashrack angle.
TL;DR: In this paper, a measurement method based on the cross-correlation of image pairs obtained from a calibrated stereoscopic vision system is presented, which consists in the generation of parametric shape and displacement forms which are directly projected on the camera models.
Abstract: The present paper addresses the problem of combined three-dimensional measurements of shape and velocity of moving free surfaces. A measurement method based on the cross-correlation of image pairs obtained from a calibrated stereoscopic vision system is presented. The underlying concept of the method consists in the generation of parametric shape and displacement forms which are directly projected on the camera models. This procedure is then integrated in an iterative optimization process so that elevation, orientation, curvature and displacement of each surface subset are accurately estimated. An application to an inclined plane flow of a non-Newtonian fluid is proposed as an alternative to conventional rheometric solutions.
TL;DR: In this paper, a procedure is introduced to obtain an instantaneous pressure field around a wing from time-resolved particle image velocimetry (TR-PIV) and particle image accelerometry (PIA) and the instantaneous fields of velocity and material acceleration are provided by the recently introduced multi-frame PIV method, fluid trajectory evaluation based on ensemble-averaged cross correlation (FTEE).
Abstract: A procedure is introduced to obtain an instantaneous pressure field around a wing from time-resolved particle image velocimetry (TR-PIV) and particle image accelerometry (PIA). The instantaneous fields of velocity and material acceleration are provided by the recently introduced multi-frame PIV method, fluid trajectory evaluation based on ensemble-averaged cross-correlation (FTEE). The integration domain is divided into several subdomains in accordance with the local reliability. The near-edge and near-body regions are determined based on the recorded image of the wing. The instantaneous wake region is assigned by a combination of a self-defined criterion and binary morphological processes. The pressure is reconstructed from a minimization process of the difference between measured and reconstructed pressure gradients in a least-square sense. This is solved sequentially according to a decreasing order of reliability of each subdomain to prevent a propagation of error from the less reliable near-body region to the free-stream. The present procedure is numerically assessed by synthetically generated 2D particle images based on a numerical simulation. Volumetric pressure fields are then evaluated from tomographic TR-PIV of a flow around a 30-degree-inclined NACA0015 airfoil. A possibility of using a different scheme to evaluate material acceleration for a specific subdomain is presented. Moreover, this 3D application allows the investigation of the effect of the third component of the pressure gradient by which the wake region seems to be affected.
TL;DR: In this paper, the authors provide a unified and comprehensive theory of structural time series models, including a detailed treatment of the Kalman filter for modeling economic and social time series, and address the special problems which the treatment of such series poses.
Abstract: In this book, Andrew Harvey sets out to provide a unified and comprehensive theory of structural time series models. Unlike the traditional ARIMA models, structural time series models consist explicitly of unobserved components, such as trends and seasonals, which have a direct interpretation. As a result the model selection methodology associated with structural models is much closer to econometric methodology. The link with econometrics is made even closer by the natural way in which the models can be extended to include explanatory variables and to cope with multivariate time series. From the technical point of view, state space models and the Kalman filter play a key role in the statistical treatment of structural time series models. The book includes a detailed treatment of the Kalman filter. This technique was originally developed in control engineering, but is becoming increasingly important in fields such as economics and operations research. This book is concerned primarily with modelling economic and social time series, and with addressing the special problems which the treatment of such series poses. The properties of the models and the methodological techniques used to select them are illustrated with various applications. These range from the modellling of trends and cycles in US macroeconomic time series to to an evaluation of the effects of seat belt legislation in the UK.
01 Apr 2003
TL;DR: The EnKF has a large user group, and numerous publications have discussed applications and theoretical aspects of it as mentioned in this paper, and also presents new ideas and alternative interpretations which further explain the success of the EnkF.
Abstract: The purpose of this paper is to provide a comprehensive presentation and interpretation of the Ensemble Kalman Filter (EnKF) and its numerical implementation. The EnKF has a large user group, and numerous publications have discussed applications and theoretical aspects of it. This paper reviews the important results from these studies and also presents new ideas and alternative interpretations which further explain the success of the EnKF. In addition to providing the theoretical framework needed for using the EnKF, there is also a focus on the algorithmic formulation and optimal numerical implementation. A program listing is given for some of the key subroutines. The paper also touches upon specific issues such as the use of nonlinear measurements, in situ profiles of temperature and salinity, and data which are available with high frequency in time. An ensemble based optimal interpolation (EnOI) scheme is presented as a cost-effective approach which may serve as an alternative to the EnKF in some applications. A fairly extensive discussion is devoted to the use of time correlated model errors and the estimation of model bias.
TL;DR: A review of the approach to extract pressure fields from flow velocity field data, typically obtained with particle image velocimetry (PIV), by combining the experimental data with the governing equations is presented in this article.
Abstract: The topic of this article is a review of the approach to extract pressure fields from flow velocity field data, typically obtained with particle image velocimetry (PIV), by combining the experimental data with the governing equations. Although the basic working principles on which this procedure relies have been known for quite some time, the recent expansion of PIV capabilities has greatly increased its practical potential, up to the extent that nowadays a time-resolved volumetric pressure determination has become feasible. This has led to a novel diagnostic methodology for determining the instantaneous flow field pressure in a non-intrusive way, which is rapidly finding acceptance in an increasing variety of application areas. The current review describes the operating principles, illustrating how the flow-governing equations, in particular the equation of momentum, are employed to compute the pressure from the material acceleration of the flow. Accuracy aspects are discussed in relation to the most dominating experimental influences, notably the accuracy of the velocity source data, the temporal and spatial resolution and the method invoked to estimate the material derivative. In view of its nature of an emerging technique, recently published dedicated validation studies will be given specific attention. Different application areas are addressed, including turbulent flows, aeroacoustics, unsteady wing aerodynamics and other aeronautical applications.
TL;DR: A review of active control of flow-induced cavity oscillations is presented in this paper, with emphasis on experimental implementation of open-and closed-loop control approaches, as well as the characteristics of various actuators, flow sensing and measurement, and control methodologies employed to date.
TL;DR: Trapped vortex combustion (TVC) as mentioned in this paper is a promising combustion concept that has been extensively studied in the application areas of aerospace propulsion, power generation and waste incineration, where a large rotating vortex can be formed in the cavity and is thus named a locked vortex.