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September 1968 - February 2011
Publications
Publications (154)
Laser Doppler Velocimeter measurements in gas flows require as low a seeding as possible. Such conditions can only be accommodated by period counters. These instruments have to process a signal with low signal to noise ratios. The smaller the number of signals, the lower the SNR. These processors have built-in noise rejection devices. One of them i...
Introduction Two-component PIV Three-component PIV Bibliography
An image-processing technique is proposed, which performs iterative interrogation of particle image velocimetry (PIV) recordings.
The method is based on cross-correlation, enhancing the matching performances by means of a relative transformation between
the interrogation areas. On the basis of an iterative prediction of the tracers motion, window o...
To be able to characterize the airflow in the presence of liquid droplets in a confined geometry, a new two-phase particle
image velocimetry (PIV) method is developed. It is based on a two-colour YAG laser and two different fluorescent dyes dissolved
in the gas-phase tracers and droplets. This approach permits to separate the images (and thus the i...
This paper proposes a specific application of the approach recently proposed by the authors to achieve an autonomous and robust
adaptive interrogation method for PIV data sets with the focus on the determination of mean velocity fields. Under circumstances
such as suboptimal flow seeding distribution and large variations in the velocity field prope...
Accurate modeling of air flow and aerosol transport in the alveolated airways is essential for quantitative predictions of pulmonary aerosol deposition. However, experimental validation of such modeling studies has been scarce. The objective of this study is to validate CFD predictions of flow field and particle trajectory with experiments within a...
In this paper the problem posed by interfaces when present in PIV measurements is addressed. Different image pre-processing,
processing and post-processing methodologies with the intention to minimize the interface effects are discussed and assessed
using Monte Carlo simulations. Image treatment prior to the correlation process is shown to be incap...
L'objectif de cette communication est l'étude de deux micro-écoulements différents au moyen d'un système de micro-PIV non inversé. Ces écoulements diffèrent entre eux par les aspects suivants: Le premier, un écoulement pulmonaire, est représentatif d'un flux stationnaire confiné. Le second, la formation de gouttelettes par un capillaire contrôlé pa...
La communication présente les diverses solutions imaginées par l'Institut von Karman (IVK) pour améliorer la technique PIV à l'étude d'écoulements à grande échelle. Cette communication est le prolongement de la communication présentée lors du congrès CFTL 2006. Les améliorations proposées et décrites dans ce papier concernent la technique d'ensemen...
Hybrid PIV-PTV approaches and pure PTV methods in general have been discussed by several authors, focusing on the way to perform the correct association between the particles images of successive given recordings. The present work is addressing the accuracy issue of such methods. An approach that correlates individual particles images is developed...
In this paper the authors show an original application to time-resolved PIV of an existing method for confidence level and
error determination, called dependent bootstrapping. Due to the high sampling frequencies the measured velocity samples are
no longer uncorrelated making classical statistical procedures not applicable. Examples show that the v...
Verifying numerical predictions with experimental data is an important aspect of any modeling studies. In the case of the lung, the absence of direct in vivo flow measurements makes such verification almost impossible. We performed computational fluid dynamics (CFD) simulations in a 3D scaled-up model of an alveolated bend with rigid walls that inc...
To better understand the human pulmonary system and governing aerosol
deposition mechanisms within the lung, an accurate description of the airflow
in the conductive and respiratory pulmonary airways is considered to be
essential. In-vivo measurements are deemed impossible due to the small scales in
the lung structure. Though numerical simulations...
This study proposes a cross-correlation based PIV image interrogation algorithm that adapts the number of interrogation windows and their size to the image properties and to the flow conditions. The proposed methodology releases the constraint of uniform sampling rate (Cartesian mesh) and spatial resolution (uniform window size) commonly adopted in...
Verifying numerical predictions with experimental data is an important aspect of any modeling studies. In the case of the lung, the absence of direct in vivo flow measurements makes such verification almost impossible. We performed computational fluid dynamics (CFD) simulations in a 3D scaled-up model of an alveolated bend with rigid walls that inc...
The flow in the wake and near-wake regions of individual Taylor bubbles rising through stagnant and co-current vertical columns of Newtonian liquids was studied, employing simultaneously particle image velocimetry (PIV) and pulsed shadowgraphy techniques (PST). Experiments were made with water and aqueous glycerol solutions covering a wide range of...
The flow around single Taylor bubbles rising in stagnant non-Newtonian solutions of polyacrylamide (PAA) polymer was studied using a technique employing simultaneous particle image velocimetry (PIV) and shadowgraphy. Solutions with different weight percentages of polymer, varying from 0.01 to 0.80 wt.%, were used to cover a wide range of flow regim...
The flow in the nose region and in the annular film around individual Taylor bubbles rising through stagnant and co-current vertical columns of liquid were studied, employing particle image velocimetry (PIV) and pulsed shadowgraphy techniques (PST) at the same time. The combined techniques enabled simultaneous determination of the bubble shape and...
Studies related to aerosol deposition in the alveolar pulmonary airways have been mostly restricted to numerical studies, which require further experimental validation. Few experimental studies have been performed extracting quantitative data due to the involved complexity accompanying the extremely low Reynolds-numbers (in the order of 0.01) encou...
Up to now the application of rainbow thermometry has been limited to particle systems possessing a uniform refractive index. This is mostly due to the absence of an appropriate data inversion algorithm that takes into account the presence of a refractive index gradient. In this paper, for the first time to our knowledge, exploiting a generalization...
A novel measuring technique for bubbly flows, named glare point velocimetry and sizing (GPVS), was developed in order to measure both bubble size and velocity with high accuracy in a 2D plane. This is accomplished by observing glare points in-focus under an observation angle of 96. When a second laser-sheet is added, even higher accuracies are obta...
The flow around single Taylor bubbles rising in non-Newtonian solutions of Carboxymethylcellulose (CMC) polymer was studied using simultaneously particle image velocimetry (PIV) and shadowgraphy. This technique made it possible to determine the correct position of the bubble interface. Solutions of polymer with weight percentage varying from 0.1 to...
In the development of new measurement techniques, increasing the resolution has always been one of the main goals. For the moment, cross-correlation algorithms such as PIV, are limited by the size of the interrogation areas. Algorithms of hybrid PIV-PTV processing, so called Super Resolution methods, are about to be mature and have shown an increas...
Rainbow techniques permit measurement of refractive indices, and hence the temperatures of liquid droplets through determination of the absolute angular position of a rainbow interference image in space. The Airy theory, which is commonly used to explain the rainbow effect, permits the determination of a unique refractive-index value, even in the p...
Unsteady or statistically steady flows are of increasing interest at the present state of research. Besides the use of statistical averages and the RMS values around the obtained mean, the fine, instantaneous details of the flow are getting important to be determined for the better understanding of the main mechanisms in the flow field. In this art...
In the present paper, a laminar cavity is analysed at very low Mach numbers. The characteristics of core-vortices are proposed and commented. The experiments were performed in an open subsonic wind tunnel using particle image velocimetry (PIV). A rectangular cavity with a length-to-depth ratio of 4 was used (shallow and open type). Three different...
Two-phase flows hold an interest in many areas of science and engineering. In the safety field, one such topic is the accidental release of flammable and toxic pressure-liquefied gases. In case of such a release, a flashing vapor explosion takes place resulting in a very dense two-phase cloud. If the released substance is flammable, this cloud can...
A simultaneous technique employing particle image velocimetry (PIV) and shadowgraphy was used to study vertical slug flow in non-Newtonian fluids. Two aqueous solutions of 0.8 and 1.0 wt% carboxymethylcellulose (CMC) were studied and the flow field around individual Taylor bubbles fully characterized. The rheological fluid properties and pipe dimen...
Improvements on the validation of a nonintrusive laser-based measurement technique are presented. This new technique, called global rainbow thermometry (GRT), is capable of determining the temperature and the size distributions of liquid droplets dispersed in a liquid or gaseous bulk. We propose a new data inversion algorithm that takes into accoun...
An experimental investigation of downward cocurrent bubbly flow is performed to determine which parameters govern the transition from bubbly flow to annular flow and how to take into account the scale of the experimental facility in the prediction of the transition from one flow regime to the other. The measurements are preformed on two water model...
The eddy structures shed in a backward facing step (BFS) flow are considered in this work. Particle image velocimetry (PIV) measurements are performed in the recirculating region located downstream of the step. These measurements are validated by comparison with data available in the literature. An automatic vortex detection algorithm is developed...
Improving spatial resolution of optical whole field velocity measurement tech-nique is a challenging task. This topic was addressed in different ways. Comple-mentary to cross-correlation methods, which are presently widely adopted, combi-nation of PIV and PTV is considered. This work discusses different issues involved in the implementation of a hy...
A recent technique of simultaneous particle image velocimetry (PIV) and pulsed shadow technique (PST) measurements, using only one black and white CCD camera, is successfully applied to the study of slug flow. The experimental facility and the operating principle are described. The technique is applied to study the liquid flow pattern around indivi...
Simultaneous measurement of velocity and concentration provides a tool for studying the turbulent diffusion. This quantity until now was mainly modeled and not measured and it plays an essential role in turbulent diffusion of pollutant.We present a new technique to measure the turbulent mass flux vector, , based on the same PIV/PTV images, employed...
Improvements on the Global Rainbow Thermometry (GRT) technique are being presented. The GRT technique allows us to study the physical properties of liquid-in-liquid and liquid-in-air dispersions. In this paper the influence of droplet non-sphericity on the size and temperature measurements of liquid droplets suspended in a liquid or a gaseous bulk...
The pairing of vortex rings in an acoustically excited jet is experimentally investigated. The acoustical forcing of the jet allows a series of particle image velocimetry (PIV) measurements to be performed at a frequency slightly lower than the frequency at which the vortex rings are shed in the shear layer. This technique, here called stroboscopic...
A new technique has been designed to optically characterize free surfaces or interfaces. This technique, called Level Detection and Recording (LeDaR), relies on a computer analysis of light intensity gradient of images provided by a CCD camera and allows obtaining temporal and spatial information in real time processing. The global frame in which t...
Heated sphere anemometers (HSA) are the most widely used instruments for low-velocity measurements in the heating, ventilation
and air-conditioning industry. Experiments were conducted to characterise the flowfield around the spherically shaped sensor
and upper probe assembly of a HSA. Particle image velocimetry was the main quantitative experiment...
Le système récent de mesure BOS fournit des résultats prometteurs qui permettent de visualiser qualitativement des gradients de densité comme lont présenté Richard et Raffel (2000). Cette étude montre quil est possible de mesurer des informations sur la concentration locale grâce à la méthode BOS dans le cas particulier dun jet 2D. Une expérienc...
Two-phase flows hold an interest in many areas of science and engineering. In the safety field, one such topic is the accidental release of flammable and toxic pressure-liquefied gases. In case of such a release, a flashing vapor explosion takes place resulting in a very dense two-phase cloud. In particular, if the released substance is flammable,...
Two-phase flows hold an interest in many areas of science and engineering. In the safety field, one such topic is the accidental release of flammable and toxic pressure-liquefied gases. In case of such a release, a flashing vapor explosion takes place resulting in a very dense two-phase cloud. In particular, if the released substance is flammable,...
In this work, the Particle Image Velocimetry (PIV) technique is used to characterise the flow around a single Taylor bubble rising through a vertical column of stagnant liquid. The experimental facility and its operating principle are described. The gas slug velocity is determined from the signals of two photocells that receive light from two laser...
The incidence of respiratory diseases such as bronchiole inflammation and asthma tends to increase. These diseases are directly linked to air pollution and to the deposition of particulate pollutants in the lungs. To prevent or treat these diseases, most therapies use drugs, which are delivered into the lungs in the form of aerosol. A better unders...
A recent technique for performing simultaneous Particle Image Velocimetry and Shadography applied for the first time to slug flow, is presented in this work. The unsteadiness of slug flow creates the need of recording the shadow of the Taylor bubbles at the precise instant and position of the PIV measurements. Therefore, this experimental technique...
A rectangular cavity with a length-to-depth ratio of 10 is characterized by means of two optical velocimetry systems: Laser Doppler Velocimetry (LDV) and Particles Images Velocimetry (PIV). Each of these two measurement systems provides a complementary contribution to the understanding of this complex flow. A detailed mean velocity field is acquire...
The sound radiated by vortex pairing in a subsonic excited jet is deduced from experimental data obtained by particle image velocimetry (PIV). We compare the performance of different formulations of vortex sound theory to predict the corresponding sound production. It is shown that assuming several times the conservation of the momentum and kinetic...
Global rainbow thermometry is a new technique for measuring the average size and temperature of spray droplets. For data inversion a global rainbow pattern is employed, which is formed by constructive interference of laser light scattered by an ensemble of spherical droplets. The non-spherical droplets and liquid ligaments provide a uniform backgro...
The state of the art in Rainbow Thermometry is presented. Rainbow Thermometry is a technique for measuring size and temperature of transparent droplets. For data inversion a rainbow pattern is employed, which is formed by a single droplet or by constructive interference of laser light scattered by an ensemble of spherical droplets. In the first cas...
This work constitutes the study and the development of an integrated PIV-PTV method, which combines the advantages of the two approaches: the robustness of PIV and the spatial resolution of PTV. The technique is a hybrid algorithm that starts by statistical evaluation of a tracer's displacement (PIV analysis) and further refines the resolution of m...
Digital particle image velocimetry and wavelet analysis are combined in this work in order to study the characteristics of the leading vortex ring generated in an impulsively starting jet flow. The wavelet analysis allows one, by virtue of its properties of selectivity in space and scale, to detect coherent structures and to compute their position...
I am unable to provide the full text of the article "Measurement Tecnhniques in Flud Dynamics". Indeed, this is a full book, published in 2001 by the von Karman Institute for Fluid Dynamics, and it is out of print since a few years. A new edition is in preparation and will be sold by the von Karman Institute, when it will become available. A one-we...
The aim of this study is to investigate airflow in the conductive pulmonary airways to contribute to a better understanding of the human pulmonary system. This experimental study deals with the investigation of steady and oscillatory flows within a 3D model of three successive generations of lung bifurcations. The experimental measurements are perf...
The purpose of this study is to investigate the blade to blade flow in an axial compressor, providing a detailed description of the entire flow-field on multiple layers through the use of Particle Image Velocimetry (PIV).
Typical problems that relate to flow seeding, light-sheet generation and camera-laser timing control are successfully dealt with...
An advanced PIV processing technique is applied to investigate the turbulent flow over a Backward Facing Step (BFS). The results are compared with Direct Numerical Simulation (DNS) and LASER Doppler Velocimetry (LDV) data available on the subject.
The work proposes an appropriate algorithm to evaluate the PIV recordings. This procedure performs a l...
A two-phase measurement technique based on the simultaneous sizing of the dispersed phase and PlV measurement of the continuous phase is presented. The referred technique has been applied to study the formation of bubbles, when air is injected into quiescent water through a single needle. The efficient application of the PlV technique to measure th...
Standard rainbow thermometry connects the scattering angle of the main rainbow maximum, generated by a single droplet, to the droplet’s refractive index and thus to its temperature. Droplet nonsphericity influences the rainbow position and therefore degrades the quality of the droplet-temperature measurement. We propose global rainbow thermometry,...
A pattern recognition technique for the investigation of large-scale coherent structures, is applied to analyze the turbulent separated flow over a backward facing step (BFS) at a Reynolds number Reh=5.0×103. The instantaneous two-dimensional velocity distribution is obtained by means of digital particle image velocimetry (D-PIV) measurements. High...
In our environment, chronic pulmonary illness due to pollution effects or asthmatic problems are increasing. To identify the contribution of pollution effect on the alterations in breath patterns, a better understanding of the human pulmonary system is needed. As a result, fields to be investigated are mostly flows in the lungs at high breathing fr...
The features of an improved algorithm for the interrogation of (digital) particle image velocimetry (PIV) pictures are described.
The method is based on cross-correlation. It makes use of a translation of the interrogation areas. Such a displacement is
predicted and corrected by means of an iterative procedure. In addition, while iterating, the me...
The aim of this study is to investigate airflow in the conductive pulmonary airways to contribute to a better understanding of the human pulmonary system. This experimental study deals with the investigation of oscillatory flows within a 2D model of three successive generations of lung bifurcations. The particle image velocimetry technique has been...
In our environment, chronic pulmonary illness due to pollution effects or asthmatic problems are increasing. To identify the contribution of pollution effect on the alterations in breath patterns, a better understanding of the human pulmonary system is needed. As a result, fields to be investigated are mostly flows in the lungs at high breathing fr...
The unsteady nature of the flow within a cascade of bifurcating branches was investigated for Reynolds numbers of 900 and 2700 in the mother branch. The cascade consists of three generations of planar symmetric bifurcations with a fixed branching angle and ratio of branch length to width. Chronological flow field measurements were carried out using...
A rainbow measurement technique is presented which measures simultaneously the size, temperature and velocity of individual droplets in a spray. The technique is based on rainbow interferometry in combination with diffraction by a wire placed in the spatial filter of the scattered-light detector. A photomultiplier detecis the wire diffraction patte...
To better understand the human pulmonary, flows within lung
bifurcations have been experimentally investigated with a new Particle
Image Velocimetry (PIV) technique. Instationarities in the flow can be
studied with this technique where both spatial and temporal information
of the entire flow field can be obtained, in providing the simultaneous
visu...
An experimental method is presented that detects whether a droplet is spherical. The method is based on a comparison between two droplet diameters deduced from two different optical interference patterns observed in a rainbow that is created by a droplet scattering laser light. Experimental validation has been carried out with a CCD camera. Once a...
The digital method previously developed by Lourenço and Riethmuller (1980) using "single Laser beam technique" was modified as "double cross-beam technique" to measure the local particle concentrations in turbulently flowing gas-solid suspensions through horizontal rectangular ducts and the two techniques were compared with each other.
The anisotropy of laser light scattered by a droplet exhibits a strong dependence on droplet size and temperature. Around the geometrical rainbow angle this dependence is such that it can be used to determine these two parameters. This determination is done with the help of the Airy theory for the rainbow to avoid an extensive calibration of the an...
The development and testing of a holographic technique capable of measuring the three velocity components in selected regions of the flow field are described. Several techniques, including laser Doppler velocimetry, hot wire and particle image velocimetry (PIV) are commonly used to measure a flow field. The advantage of the PIV technique is that it...
A laminar approach of the melt-spinning process is presented, using nondimensionalized momentum and thermal boundary-layer equations. The momentum boundary layer along a yarn of circular cross section in axial flow is investigated for two types of boundary conditions; the quasi-similar solution is computed for both a semi-infinite body and a contin...
A nonintrusive laser technique, based on the detection of a rainbow, is presented that permits one to determine simultaneously the temperature and size of droplets. Therefore the Airy theory for a rainbow and a calibration rainbow pattern at isothermal conditions are applied. Rainbow patterns coming from droplets in the millimeter range have been r...
In order to study the correlation between valvular regurgitation flows and the power spectrum (PS) of Doppler recordings, the authors have developed an in-vitro model of a regurgitation based on a stationary turbulent free jet. Flows up to 4 l/min through orifices ranging from 2 to 4.5 mm in diameter are available. The authors' model has been valid...
The basic principle of the technique of Particle Image Velocimetry is
presented. The different methods available are discussed and advantages
of each of them are exposed. The latest fully optical processing methods
are compared to recent video based techniques. The extension of the
measurements technique to 3D and the suppression of the directional...
The effect of the length scale on wind-tunnel simulation is evaluated by comparing the results obtained from similar experiments performed in two differently sized wind tunnels. One experiment was carried out in the EPA (U.S. Environmental Protection Agency) meteorological wind tunnel (3.7 m wide, 2.1 m high and 18.3 m long). A similar study at a g...
A new technique for simultaneous three-dimensional velocity measurements in a flowfield is presented in this paper. The technique
uses double exposure holographic recording of a seeded flow and nonlinear optical processing of the holographically recorded
information, to produce interference fringes representing the 3-D velocity vector at a selected...
A laser velocimetry technique developed to measure low level turbulence is described. The ultimate objective of the research is to detect the surface layer limit on a model in a transonic air flow. The use of laser velocimetry in the study of turbulence should allow turbulence of a few thousands in size to be detected. The detectors used in the stu...
The uncertainty in particle image displacement velocimetry measurements is described with regard to application of the methodology to the flow in a centrifugal pump. Attention is given to the sources of inaccuracy, to the reduction or control of their effects, and to the evaluation of the magnitude of the overall uncertainty achieved. It is shown t...
The aim of this contribution is to describe a study of pulmonary flows performed using both experimental and computational methods.
The lung consists of a network of bifurcating tubes through which air flows from the trachea through 17 generations of airways where convective processes dominate to the 6 further generations (alveolar zone) where gas...
