Vortex Structure in the Wall Region of an Impinging Plane Jet

The work presented here comes within a research program dealing with vortex detection in the impingement region of a planar jet. In this study, experiments have been performed for a submerged turbulent water slot jet impinging normally on a flat plate, and an emphasis was put on the flow field characteristics. For this purpose, particle image velocimetry (PIV) have been employed. A comprehensive fluid mechanical data includes instantaneous and mean flow field, variance of normal and cross velocity fluctuations have been presented. The present work is also concerned with the flow structure in the impingement region where the transfers (heat/mass) occur. An attempt has been made to understand the flow structure by employing the vortex detection criteria on the instantaneous velocity vector field. Accordingly, the PIV measurements were carried out for four different Reynolds numbers: 3000, 6000, 11000 and 16000, and at three different planes: a plane parallel to the impingement plate, transverse plane of the jet and a plane perpendicular to the jet. A method of filtration, based on proper orthogonal decomposition (POD) technique was applied first to the instantaneous velocity and filtered velocity database is then used for vortex detection. Further, the results about the size, shape, spatial distribution and energy content of the detected vortices have been provided

Vortex structure in the wall region of an impinging plane jet

La publication est référencée chez l'éditeur dans le volume 4, n°3, pp. 61-69.Issu de : CICME 10 - 2th International conference on energy conversion and conservation, Hammamet, TUNISIA, April 22-25, 2010International audienceThe work presented here comes within a research program dealing with vortex detection in the impingement region of a planar jet. In this study, experiments have been performed for a submerged turbulent water slot jet impinging normally on a flat plate, and an emphasis was put on the flow field characteristics. For this purpose, particle image velocimetry (PIV) have been employed. A comprehensive fluid mechanical data includes instantaneous and mean flow field, variance of normal and cross velocity fluctuations have been presented. The present work is also concerned with the flow structure in the impingement region where the transfers (heat/mass) occur. An attempt has been made to understand the flow structure by employing the vortex detection criteria on the instantaneous velocity vector field. Accordingly, the PIV measurements were carried out for four different Reynolds numbers: 3000, 6000, 11000 and 16000, and at three different planes: a plane parallel to the impingement plate, transverse plane of the jet and a plane perpendicular to the jet. A method of filtration, based on proper orthogonal decomposition (POD) technique was applied first to the instantaneous velocity and filtered velocity database is then used for vortex detection. Further, the results about the size, shape, spatial distribution and energy content of the detected vortices have been provided

Analyse expérimentale multi-échelles des interactions entre un écoulement et une paroi par PIV et polarographie (application à un jet plan immergé et confiné en impact )

Ce travail consiste en l étude expérimentale des mécanismes de transferts à l impact d un jet plan d eau immergé, vertical, confiné et turbulent. Ces mécanismes se présentent sous forme de rouleaux tourbillonnaires contrarotatifs évoluant transversalement au plan du jet. Deux techniques de mesures expérimentales ont été utilisées : la PIV, et la polarographie. Dans une première étape, pour bien extraire les structures tourbillonnaires, différents critères de détection de tourbillons ont été testés sur un champ tourbillonnaire analytique étalon. Le critère 2 a été retenu vu son efficacité. La seconde étape a été consacrée aux mesures expérimentales par PIV et polarographie. Les bruits de mesures sur les champs de vitesse obtenus par PIV ont été filtrés par la technique de POD. La PIV classique a servi à caractériser l écoulement, en analysant les composantes moyennes et fluctuantes de la vitesse. Ceci a permis, d une part, de délimiter les différentes régions du jet, et en particulier la zone d impact, et d autre part, de caractériser les tourbillons présents dans cette zone (tailles, formes, intensités tourbillonnaires, etc.). Par la suite, l étude a été focalisée sur la zone d impact du jet en utilisant la PIV rapide et l électrochimie. Les vitesses mesurées par PIV rapide en proche paroi ont permis de caractériser les échelles de turbulence et de se situer par rapport aux lois de paroi. A partir des mesures de vitesse, l analyse des modes spatiaux POD les plus énergétiques a contribué à localiser les zones les plus sollicitées par les structures tourbillonnaires à l impact du jet, et où les sondes électrochimiques ont été implantées. En utilisant, la technique électrochimique, nous avons déterminé le gradient pariétal de vitesse dans ces zones. Une synchronisation temporelles entre les techniques de PIV rapide et d électrochimie a permis de monter la bonne concordance entre les gradients pariétaux et instantanés de vitesse déterminés par ces deux méthodes.This work is an experimental study of transfer mechanisms at the impingement of a plane water submerged vertical confined turbulent jet. Transfers are enhanced at the impingement due to the presence of large-scale turbulent structures appearing in the form of elongated cell rolls, whose main axis is perpendicular to the midplane of the jet. Two experimental measurement techniques were used in this study: PIV (low and high-speed) and electrochemical method (polarography). In the first part of this study, we tested and calibrated different vortex detection criteria on a standard analytical velocity field. Among these criteria, the function 2 was found to correctly detect the centre core of vortices. The second part of this work was devoted to experimental measurements by PIV and polarography. Noise measurements on the velocity fields obtained by PIV were filtered by the POD technique. Standard PIV technique was used to characterize the flow by analyzing the mean and turbulent components of velocity. This allowed, firstly, delineating the different regions of the jet, particularly the impingement region, and secondly, characterizing the vortices in this region (size, shape, vortical intensity, etc.). Subsequently, the study was focused on the impingement region of the jet using high-speed PIV and electrochemical method. The velocity field in the vicinity of the impingement surface was examined. The applicability of the wall laws on the target surface was checked. The analysis of the most energetic spatial modes issued from velocity field decomposition by POD, showed the most sheared positions at the impingement plate. Shear wall stress was evaluated at these positions using polarography technique. Subsequently, synchronized measurements show a good agreement between high-speed PIV and electrochemical techniques for the evaluation of the wall shear stresses.NANTES-BU Sciences (441092104) / SudocSudocFranceF

Vortex structure in the wall region of an impinging plane jet

La publication est référencée chez l'éditeur dans le volume 4, n°3, pp. 61-69.Issu de : CICME 10 - 2th International conference on energy conversion and conservation, Hammamet, TUNISIA, April 22-25, 2010International audienceThe work presented here comes within a research program dealing with vortex detection in the impingement region of a planar jet. In this study, experiments have been performed for a submerged turbulent water slot jet impinging normally on a flat plate, and an emphasis was put on the flow field characteristics. For this purpose, particle image velocimetry (PIV) have been employed. A comprehensive fluid mechanical data includes instantaneous and mean flow field, variance of normal and cross velocity fluctuations have been presented. The present work is also concerned with the flow structure in the impingement region where the transfers (heat/mass) occur. An attempt has been made to understand the flow structure by employing the vortex detection criteria on the instantaneous velocity vector field. Accordingly, the PIV measurements were carried out for four different Reynolds numbers: 3000, 6000, 11000 and 16000, and at three different planes: a plane parallel to the impingement plate, transverse plane of the jet and a plane perpendicular to the jet. A method of filtration, based on proper orthogonal decomposition (POD) technique was applied first to the instantaneous velocity and filtered velocity database is then used for vortex detection. Further, the results about the size, shape, spatial distribution and energy content of the detected vortices have been provided

Détection expérimentale de structures tourbillonnaires au sein d’un jet plan confiné en impact

Nous présentons les résultats de mesures PIV résolues en temps réalisées sur un double jet plan frappant une plaque plane en préalable à l’analyse de la dynamique de la zone d’impact de ce type d’écoulements. Les structures de sillage et de couche de mélange présentes sur les clichés ont été détectées à partir du critère gamma2 proposé par Graftieaux (2001) puis caractérisées. Les résultats sont comparés à ceux de la littérature. Les limites et les difficultés de la méthode sont discutées

Volumetric velocity measurements (V3V) on turbulent swirling flows

International audienceThis paper presents some results of Volumetric V3V 3D3C velocity measurements on a turbulent flow from a swirl burner. The flow out from the burner used is highly three-dimensional. The study aims at using a system of instantaneous 3D velocity measurements in order to characterize the turbulent swirling flow. The burner used consists of two coaxial tubes with a swirler placed in an annular part supplying the oxidant flow. The central pipe delivers the fuel radially (in the case of reacting flow) through eight holes symmetrically distributed on the periphery of the tube. The burner is placed at the bottom of a combustion chamber and the flow develops vertically along the confinement. The Volumetric 3-component Velocimetry V3V® technique commercialized by TSI is used for 3D velocity measurements in a non reacting flow. The measurement volume above the burner is located at 1.3Db (=49.4 mm) and is 50×50×22 mm3. The operating conditions considered in this study are 4.67 m/s of bulk velocity, Re=7531 of Reynolds number and Sn=1.4 of swirl number. There are very limited works on the application V3V technique on fluid flows. This paper presents the first results concerning an isothermal non-reacting gas flow. Instantaneous and mean velocity 3D3C volumes are measured and shown. Streamlines and velocity iso-surfaces are also analyzed together with different velocity profiles. The results are compared to previous SPIV (Stereoscopic Particle Image Velocimetry) measurements performed by the authors. A good agreement is found between the results of both techniques; the discrepancy did not exceed 10%. V3V results allowed a fine description of 3D aspects of the flow including the recirculation zone and the annular zone with swirling jet effects. The swirling part of the flow and the central recirculation zone are clearly identified by 3D fields of velocities and streamlines. Velocity volume indicates the presence of a central zone with a negative longitudinal velocity, which can reach −1 m/s at the burner center. Under the swirl effect, the tangential velocity is relatively high, particularly in the annular zone of the burner. Indeed, this velocity is varied between 3 and −3 m/s for a bulk velocity of 4.7 m/s