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Characteristics of a jet in the vicinity of a free surface / Jiahao Tian in Transactions of the ASME . Journal of fluids engineering, Vol. 134 N° 3 (Mars 2012) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 134 N° 3 (Mars 2012) . - 12 p. Titre : Characteristics of a jet in the vicinity of a free surface Type de document : texte imprimé Auteurs : Jiahao Tian, Auteur ; Roussinova Vesselina, Auteur ; Ram Balachandar, Auteur Année de publication : 2012 Article en page(s) : 12 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Round  turbulent  jet;  free  surface;  velocity Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : In this study, the characteristics of a round turbulent jet in the vicinity of a free surface are investigated. The jet issued from a nozzle located at a depth five times the nozzle diameter (d = 10 mm) below and parallel to the free surface. The jet exit velocity was 2.8 m/s and the resulting Reynolds number was 28,000. Instantaneous two-dimensional PIV measurements were obtained in the vertical central plane and in several horizontal planes at various distances (y/d = 0,±1,±2,±3± 4) from the axis of the nozzle. All fields-of-view were positioned at streamwise locations in the range of 28 < x/d < 62, where the jet interacts significantly with the free surface. The results reveal that the behavior of the surface jet is very similar to that of the free jet before it interacts with the free surface which occurs at about x/d = 30. Beyond this, the velocity normal to the free surface is diminished and those parallel to the free surface are enhanced in the region near the free surface. In the horizontal plane near the free surface (y/d = +4), the spreading of the surface jet is significantly greater than that of the free jet. The mean lateral flow in this region tends to be outward everywhere for the surface jet, while the opposite trend occurs in the free jet. Turbulence intensities in all three directions are reduced by the effect of the free surface confinement. Near the free surface, at y/d = +4, unlike the single peak streamwise turbulence intensity profile noticed in the case of the free jet, the off-axis double peaks reappear in the case of the surface jet. The magnitude of shear stress in the vertical central plane of the surface jet is smaller than that noticed in the free jet near the free surface. In identical horizontal planes, the shear stress (-[overline uw]) profiles are similar in both free jets and surface jets in regions where the interaction with the free surface is not significant (x/d [approximate] 30). As the downstream distance increases near the free surface, the magnitudes of the shear stress profiles are larger compared to that of the free jet. An increase in the normal component of vorticity is observed in the horizontal planes near the free surface. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JFEGA4000134000003 [...] [article] Characteristics of a jet in the vicinity of a free surface [texte imprimé] / Jiahao Tian, Auteur ; Roussinova Vesselina, Auteur ; Ram Balachandar, Auteur . - 2012 . - 12 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 134 N° 3 (Mars 2012) . - 12 p. Mots-clés : Round  turbulent  jet;  free  surface;  velocity Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : In this study, the characteristics of a round turbulent jet in the vicinity of a free surface are investigated. The jet issued from a nozzle located at a depth five times the nozzle diameter (d = 10 mm) below and parallel to the free surface. The jet exit velocity was 2.8 m/s and the resulting Reynolds number was 28,000. Instantaneous two-dimensional PIV measurements were obtained in the vertical central plane and in several horizontal planes at various distances (y/d = 0,±1,±2,±3± 4) from the axis of the nozzle. All fields-of-view were positioned at streamwise locations in the range of 28 < x/d < 62, where the jet interacts significantly with the free surface. The results reveal that the behavior of the surface jet is very similar to that of the free jet before it interacts with the free surface which occurs at about x/d = 30. Beyond this, the velocity normal to the free surface is diminished and those parallel to the free surface are enhanced in the region near the free surface. In the horizontal plane near the free surface (y/d = +4), the spreading of the surface jet is significantly greater than that of the free jet. The mean lateral flow in this region tends to be outward everywhere for the surface jet, while the opposite trend occurs in the free jet. Turbulence intensities in all three directions are reduced by the effect of the free surface confinement. Near the free surface, at y/d = +4, unlike the single peak streamwise turbulence intensity profile noticed in the case of the free jet, the off-axis double peaks reappear in the case of the surface jet. The magnitude of shear stress in the vertical central plane of the surface jet is smaller than that noticed in the free jet near the free surface. In identical horizontal planes, the shear stress (-[overline uw]) profiles are similar in both free jets and surface jets in regions where the interaction with the free surface is not significant (x/d [approximate] 30). As the downstream distance increases near the free surface, the magnitudes of the shear stress profiles are larger compared to that of the free jet. An increase in the normal component of vorticity is observed in the horizontal planes near the free surface. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JFEGA4000134000003 [...]

Revisiting turbulence in smooth uniform open channel flow / Roussinova Vesselina in Journal of hydraulic research, Vol. 46 extra issue (2008) 

Public ISBD [article]  in Journal of hydraulic research > Vol. 46 extra issue (2008) . - p. 36-48 Titre : Revisiting turbulence in smooth uniform open channel flow Titre original : Révision de la tubulence dans un écoulement uniforme en canal ouvert lisse Type de document : texte imprimé Auteurs : Roussinova Vesselina, Auteur ; Nihar Biswas, Auteur ; Ram Balachandar, Auteur Article en page(s) : p. 36-48 Note générale : Hydraulique Résumé en Français Langues : Anglais (eng) Mots-clés : Open  channel  flow  Turbulence  Quadrant  analysis  Channel  aspect  ratio Index. décimale : 627 Ingénierie des cours d'eau naturels, des ports, des rades et des cotes. Installations de navigation, de dragage, de récupération et de sauvetage. Barrages et centrales électriques hydrauliques Résumé : This study reexamines the mean velocity scaling as well as higher order turbulent moments in a uniform smooth open channel flow with three different aspect ratios. In the overlap region, the velocity profiles follow the classical logarithmic law. In the outer region, the mean velocity data at various aspect ratios collapse on to each other only when the length scale is suitably modified. This length scale is defined on the basis of a region of constant turbulence intensity close to the free surface and is equal to the depth of flow at large aspect ratios. The proposed new length scaling also provides for a positive value of the wake parameter. Furthermore, turbulence distributions including that of the Reynolds shear stress, and triple correlations ( and ) collapse onto a single line making them nearly independent of aspect ratio. Quadrant decomposition of the velocity data was used to quantify the differences in the turbulence structure at the three channel aspect ratios. The quadrant analysis shows that the turbulence in open channel is similar to that in both turbulent boundary layers and flow in two-dimensional channels when all turbulent events are included. When only the extreme events are considered, differences between open channel flow and turbulent boundary layers become significant. The conditional quadrant analysis reveals that the violent ejections do penetrate into the flow and they are responsible for producing large portion of the Reynolds shear stress. Some effects of aspect ratio are revealed when the ratio of the ejection to sweep events are calculated. The turbulent events with the higher aspect ratios tend to be closer to the two-dimensional channel data. DEWEY : 627 ISSN : 0022-1686 RAMEAU : Turbulence En ligne : http://www.journalhydraulicresearch.com/ [article] Revisiting turbulence in smooth uniform open channel flow = Révision de la tubulence dans un écoulement uniforme en canal ouvert lisse [texte imprimé] / Roussinova Vesselina, Auteur ; Nihar Biswas, Auteur ; Ram Balachandar, Auteur . - p. 36-48. Hydraulique Résumé en Français Langues : Anglais (eng) in Journal of hydraulic research > Vol. 46 extra issue (2008) . - p. 36-48 Mots-clés : Open  channel  flow  Turbulence  Quadrant  analysis  Channel  aspect  ratio Index. décimale : 627 Ingénierie des cours d'eau naturels, des ports, des rades et des cotes. Installations de navigation, de dragage, de récupération et de sauvetage. Barrages et centrales électriques hydrauliques Résumé : This study reexamines the mean velocity scaling as well as higher order turbulent moments in a uniform smooth open channel flow with three different aspect ratios. In the overlap region, the velocity profiles follow the classical logarithmic law. In the outer region, the mean velocity data at various aspect ratios collapse on to each other only when the length scale is suitably modified. This length scale is defined on the basis of a region of constant turbulence intensity close to the free surface and is equal to the depth of flow at large aspect ratios. The proposed new length scaling also provides for a positive value of the wake parameter. Furthermore, turbulence distributions including that of the Reynolds shear stress, and triple correlations ( and ) collapse onto a single line making them nearly independent of aspect ratio. Quadrant decomposition of the velocity data was used to quantify the differences in the turbulence structure at the three channel aspect ratios. The quadrant analysis shows that the turbulence in open channel is similar to that in both turbulent boundary layers and flow in two-dimensional channels when all turbulent events are included. When only the extreme events are considered, differences between open channel flow and turbulent boundary layers become significant. The conditional quadrant analysis reveals that the violent ejections do penetrate into the flow and they are responsible for producing large portion of the Reynolds shear stress. Some effects of aspect ratio are revealed when the ratio of the ejection to sweep events are calculated. The turbulent events with the higher aspect ratios tend to be closer to the two-dimensional channel data. DEWEY : 627 ISSN : 0022-1686 RAMEAU : Turbulence En ligne : http://www.journalhydraulicresearch.com/