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This study aims to investigate the effect of streamwise length on the wake characteristics of submerged sharp-edged bluff bodies in the presence of an underbody gap using large eddy simulation. To this end, three bodies with identical width (W) and height (h), but varying only in their streamwise lengths (L) were employed resulting in streamwise elongation ratios of L/h = 1, 2, and 3, respectively. The underbody gap between the bottom face of the body and the wall was fixed at 0.14 h for all cases. A fully developed turbulent boundary layer with a thickness of 3.6 h was used as the approaching flow. It was noted that the mean flow and turbulent stresses were significantly affected by the streamwise length. Premultiplied frequency spectra of the velocity fluctuations were utilized to examine the fluctuating properties of the wake. A single dominant vortex shedding frequency was observed for L/h = 1 and 3, whereas dual mode vortex shedding was noted for L/h = 2. The latter case exhibited an intermittent reattachment on the top surface of the body. The fluid structures evaluated using the λ 2 criterion, indicated that they were strongly influenced by L/h. Interestingly, even with the presence of a gap, a weak horseshoe vortex which occurred intermittently was captured close to the bed for the three cases. [ABSTRACT FROM AUTHOR]

The purpose of the present study is to investigate the influence of aspect ratio on the higher- order statistics of velocity fluctuations, conditional statistics, turbulent kinetic energy (TKE) fluxes, TKE budget, and Reynolds stress anisotropy in hydraulically rough narrow open channel flow (OCF). In the experiments, the aspect ratios were maintained low and varied between 2.5 and 4. The velocities were measured with an acoustic Doppler velocimeter (ADV). The higher-order moments, quadrant analysis, and TKE budget from the present experiments were compared with available literature data in wide and narrow OCFs to elucidate the effect of the aspect ratio. In this analysis, the third-order moments of velocity fluctuations were found to be sensitive to the aspect ratio in the outer region. The fractional contributions of all quadrant events are approximately equal in magnitude in lower aspect ratio flows, whereas ejections and sweeps are the dominant events as the aspect ratio increases. The upward transfer of TKE flux increases in the outer layer with increase in aspect ratio. In the inner layer, the TKE production and rate of dissipation are found to be increasing with decreasing aspect ratio. Therefore, the production and dissipation of TKE are dependent on the aspect ratio of the flow. The analysis of Reynolds stress AIM reveals that for low aspect ratio flows turbulence tends to attain rod-like axisymmetric turbulence only in the intermediate layer whereas for higher aspect ratio, turbulence attains rod-like axisymmetric turbulence throughout the depth. Key words: aspect ratio, turbulence, narrow open channel flow, quadrant analysis, higher-order moments, turbulent kinetic energy budget, anisotropy invariant map. Le but de la presente etude est d'examiner les effets du rapport de forme sur les statistiques d'ordre superieur des fluctuations de vitesse, les statistiques conditionnelles, les flux d'energie cinetique turbulente (ECT), le bilan de l'ECT et l'anisotropie de contrainte de Reynolds dans un ecoulement dans un etroit canal a surface libre (ECSL) hydrauliquement rugueux. Dans les experiences, les rapports de forme ont ete maintenus bas et variaient entre 2,5 et 4. Les vitesses ont ete mesurees avec un velocimetre Doppler acoustique (VDA). Les moments d'ordre superieur, l'analyse des quadrants et le bilan de l'ECT des experiences actuelles ont ete compares aux donnees disponibles de la litterature au sujet des ecoulements dans des canaux larges et etroits a surface libre pour elucider l'effet du rapport de forme. Dans cette analyse, les moments de fluctuations de vitesse du troisieme ordre se sont reveles sensibles au rapport de forme dans la region exterieure. Les contributions fractionnelles de tous les evenements quadrants sont approximativement egales en magnitude dans les ecoulements de rapport de forme inferieur, tandis que les ejections et les balayages sont les evenements dominants a mesure que le rapport de forme augmente. Le transfert vers le haut du flux d'ECT augmente dans la couche externe avec l'augmentation du rapport de forme. Par consequent, la production et la dissipation de l'ECT dependent du rapport de forme de l'ecoulement. L'analyse des contraintes de Reynolds de la carte anisotropie invariante (<< AIM >>) revele que pour les ecoulements a faible rapport de forme, la turbulence tend a atteindre la turbulence axisymetrique de tige seulement dans la couche intermediaire, tandis que pour un rapport de forme plus eleve, la turbulence atteint une turbulence axisymetrique de tige dans toute la profondeur. Mots-cles : rapport de forme, turbulence, ecoulement dans un etroit canal a surface libre (ECSL), analyse des quadrants, moments d'ordre superieur, bilan d'energie cinetique turbulente, carte anisotropie invariante (<< anistropy invariant map, AIM >>)., Introduction Open channel flow (OCF) can be classified as either narrow or wide based on the ratio of the width of the channel to the depth of the flow (Nezu [...]

Confined jets occur in many engineering applications including combustion chambers, jet pumps, and chemical reactors. The effects of axisymmetric confinement on the vortical structures identified in a turbulent jet are investigated using large eddy simulation at a Reynolds number of 30 000 (based on nozzle exit conditions) and expansion ratio (chamber-to-nozzle diameter ratio) of five. The results obtained from the confined jet are compared with those of a free jet under the same nozzle exit flow conditions. A prominent recirculation zone forms between the expanding jet and the confining wall, resulting in early shear layer distortion and a shorter interaction length in the confined jet (0.85 jet diameters) compared to the free jet (1.15 jet diameters). Using the λ2 criterion for vortex identification, two dominant structural modes are identified in the near-exit region of the free jet: ring and helical modes. However, in the confined jet, the helical mode is absent, and the turbulent confined fluid accelerates the breakup of the ring vortices. The interaction of the secondary line vortices with the breaking structures leads to the formation of new hairpin-like vortices, which also contribute to further vortex breakup. These results explain the enhanced mixing performance of confined jets as the mixing is directly tied to the breakup of large vortical structures. Proper orthogonal decomposition modes are also presented to identify the structures/events with the highest contribution to the total turbulent kinetic energy in both flow fields. [ABSTRACT FROM AUTHOR]

Three-dimensional Reynolds-Averaged Navier-Stokes simulations have been carried out to evaluate the flow past ground-mounted solar panels at different flow configurations. Initially, the flow past a stand-alone solar panel consisting of four individual sub-panels in a 2x2 arrangement is considered. The effects of the lateral gap spacing between sub-panels, the ground clearance, and the wind direction on the wind loading of the full panel have been analyzed. Simulations of the flow past solar panels in an arrayed configuration are also conducted to investigate the effect of longitudinal spacing between the panels on the wind loading. Results from the flow past the stand-alone panel reveal that the structure experiences maximum values of wind loading at two azimuthal wind directions of θ = 0° and 180°. The results also show that the two bottom panels experience larger mean wind loading compared to the top panels. The introduction of gap spacing between the panels changes the flow structure in the wake region, contributing to the formation and shedding of additional vortices, which increase in size with increased gap spacing. Although the introduction of gap spacing results in reduced mean wind forces, it produces regions that experience large wind loading. Increase of the ground clearance also causes larger mean wind loading on the panels. A proper choice of longitudinal spacing between the panels forming the array can significantly reduce the lift by taking advantage of the sheltering effect. Key words: CFD, solar panel, wind loading, gap spacing, ground clearance, array. Des simulations tridimensionnelles d'equation de Navier-Stokes a moyenne de Reynolds ont ete realisees afin d'evaluer le mouvement de l'air passant pres de panneaux solaires installes sur le sol pour differentes configurations d'ecoulement. Au depart, le debit d'air circulant pres d'un panneau solaire autonome comportant quatre sous-panneaux individuels selon une configuration de 2 sur 2 a ete considere. Les effets de l'espacement lateral entre les sous- panneaux, la distance au sol et la direction des vents sur la charge exercee par le vent sur le panneau complet ont ete analyses. Des simulations des debits d'air passant autour des panneaux solaires dans une configuration en reseau ont egalement ete realisees pour examiner l'effet de l'espacement longitudinal entre les panneaux sur la charge exercee par le vent. Les resultats pour le debit d'air circulant pres du panneau solaire autonome montrent que la structure subit des valeurs maximales de charge exercee par le vent pour deux directions de vent azimutales de θ = 0° and 180°. Les resultats montrent aussi que les deux panneaux du bas subissent une plus forte charge exercee par le vent par rapport aux panneaux du haut. L'introduction d'un espacement entre les panneaux change la structure du debit d'air dans le sillage, contribuant a la formation et a la perte de vortex additionnels dont les dimensions augmentent en fonction de l'espacement. Bien que l'introduction d'un espacement reduise les forces moyennes de vent, elle produit des regions qui connaissent de fortes charges exercee par le vent. L'augmentation de la distance du sol cause aussi une charge exercee par le vent superieure sur les panneaux. Un bon choix de l'espacement longitudinal entre les panneaux formant le reseau peut reduire significativement le soulevement exerce en prenant avantage de l'effet d'abri de protection. [Traduit par la Redaction] Mots-cles : mecanique des fluides numerique, panneau solaire, charge exercee par le vent, espacement, distance au sol, reseau., 1. Introduction The use of solar collectors to deliver an economically feasible green energy resource has increased in recent years. To facilitate ease of maintenance and enhance air ventilation, solar [...]

The flow recovery in the wake of a surface-mounted flat plate is investigated in an open channel. The plate with a thickness-to-chord ratio (t/c) of 0.12 is placed with the chord parallel to the flow. The characteristics of the mean velocity and higher-order statistics obtained along the wake axis upstream and downstream of the plate are discussed in the presence of bed roughness. Inner scaling of the mean velocity profile shows a depression in the outer region of the flow. The near-wall portion of the velocity profile in the plate wake region was found to recover faster to the upstream state. The profiles of the turbulent intensity in the plate wake deviate from the upstream profiles and recover gradually with downstream distance. The upstream turbulent intensities for the wire-mesh rough surface peak at farther wall normal locations compared to those of the sand grain and smooth surfaces. A similar roughness effect was observed at the downstream locations amidst the distorted flow, especially, in the intermediate and far wake regions. In the near- and intermediate-wake regions, both the velocity skewness and flatness factors data for the rough walls were higher compared to the data for the smooth surface. For all surfaces, even at the last measuring station (x = 200t) considered in the study, the skewness and flatness factors were found to be still recovering to the upstream condition. Key words: open channel flow, rough wall boundary layer flow, flow recovery, flat plate, wake flow. Le retablissement du debit dans le sillage d'une plaque plane installee en surface est examine dans un canal a surface libre. La plaque, dont le rapport de l'epaisseur a la corde est de 0,12, est installee avec la corde parallele a l'ecoulement. Les caracteristiques de la vitesse moyenne et les statistiques de niveau superieur obtenues le long de l'axe de sillage en amont et en aval de la plaque sont abordees en rapport avec la rugosite du lit. La mise a echelle du profil de vitesse moyenne interne montre une depression dans la region externe de l'ecoulement. La portion du profil de vitesse pres de la paroi dans la region du sillage de la plaque revient plus vite a l'etat present en amont. Les profils de l'intensite de la turbulence dans le sillage de la plaque s'eloignent des profils en amont et reprennent graduellement plus loin en aval. Les intensites turbulentes en amont de la surface rugueuse du grillage metallique atteignent une intensite maximale plus loin aux emplacements normaux sur le mur par rapport a celles observees pour les surfaces en sable et lisses. Un effet de rugosite similaire a ete remarque aux endroits en aval dans l'ecoulement deforme, plus particulierement dans les regions intermediaires et eloignees du sillage. Dans les regions intermediaries et rapprochees du sillage, les donnees des facteurs d'asymetrie de la vitesse et de planeite des murs rugueux etaient plus elevees que les donnees pour une surface lisse. Il a ete revele que les facteurs d'asymetrie et de planeite de toutes les surfaces, meme a la derniere station de mesure (x = 200t)del'etude, etaient toujours en recuperation des conditions en amont. Mots-cles : ecoulement en canal a surface libre, ecoulement de la couche limite a une paroi rugueuse, retablissement du debit, plaque plane, sillage. [Traduit par la Redaction], 1. Introduction The flow field behind surface mounted objects has been studied extensively. Examples of such flows are many and include the fluid-structure interaction involving flow past buildings, mixing of [...]

This paper investigates an isothermal free water jet discharging horizontally from a circular nozzle (9 mm) into a stationary body of water. The jet exit velocity was 2.5 m/s and the exit Reynolds number was 22,500. The large-scale structures in the far field were investigated by performing a proper orthogonal decomposition (POD) analysis of the velocity field obtained using a particle image velocimetry system. The number of modes used for the POD reconstruction of the velocity fields was selected to recover 40% of the turbulent kinetic energy. A vortex identification algorithm was then employed to quantify the size, circulation, and direction of rotation of the exposed vortices. A statistical analysis of the distribution of number, size, and strength of the identified vortices was carried out to explore the characteristics of the coherent structures. The results clearly reveal that a substantial number of vortical structures of both rotational directions exist in the far-field region of the jet. The number of vortices decreases in the axial direction, while their size increases. The mean circulation magnitude is preserved in the axial direction. The results also indicate that the circulation magnitude is directly proportional to the square of the vortex radius and the constant of proportionality is a function of the axial location. [DOI: 10.1115/1.2813137] Keywords: axisymmetric turbulent free jet, coherent structures, PIV, POD