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Buoyancy dominated He–O2 separated jet mixing in a tubular reactor / Ankur Deep Bordoloi in Transactions of the ASME . Journal of fluids engineering, Vol. 130 N° 9 (Septembre 2008) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 9 (Septembre 2008) . - 13 p. Titre : Buoyancy dominated He–O2 separated jet mixing in a tubular reactor Type de document : texte imprimé Auteurs : Ankur Deep Bordoloi, Auteur ; P. K. Panigrahi, Auteur Année de publication : 2009 Article en page(s) : 13 p. Note générale : Fluids engineering Langues : Anglais (eng) Mots-clés : Two  variable-density  jets;  digital  particle  image  velocimetry  technique;  separated  jet Résumé : Mixing of two variable-density jets, one of which is essentially a negatively buoyant jet (He) and the other a nonbuoyant jet (O2) is studied experimentally using digital particle image velocimetry technique for separated nozzle geometry. Two jets are separated from each other, i.e., He jet exit plane is located upstream of the O2 jet exit plane. Experiments were carried out keeping the nonbuoyant O2 jet at constant Reynolds number (Re2=245) and varying the Richardson number (Ri1=1.8,4.7,16.4) of the buoyant He jet. The interaction between two jets as a function of buoyancy strength of helium jet is investigated. The flow visualization images clearly demonstrate the growth and shape of buoyant jet as a function of Richardson number. Mean velocity and vorticity field results provide quantitative picture about the mixing and interaction between the two jets. The stream trace results show the flow structures, i.e., recirculation zone and foci of vortex structures as a function of Richardson number. The mixing between two jets takes place at far downstream region for low Richardson number (Ri1=1.8). At high Richardson number (Ri1=16.4), the buoyant He jet is located near its exit plane without any direct interaction with the O2 jet. At the intermediate Richardson number (Ri1=4.7), the buoyant jet encroaches the nonbuoyant O2 jet at a favorable penetration distance and a good amount of mixing between the two jets take place. The jet growth results based on the y0.5-location development in the streamwise direction clearly demonstrate the interaction between the He and O2 jets in the interjet region. The entrainment coefficient, vorticity magnitude, and turbulent kinetic energy magnitude are maximum at the intermediate Richardson number (Ri1=4.7) demonstrating direct relationship among each other. The mixing between buoyant He jet and nonbuoyant O2 jet is a function of both shear between the two jets and the strength of buoyant plume. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27337 [...] [article] Buoyancy dominated He–O2 separated jet mixing in a tubular reactor [texte imprimé] / Ankur Deep Bordoloi, Auteur ; P. K. Panigrahi, Auteur . - 2009 . - 13 p. Fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 130 N° 9 (Septembre 2008) . - 13 p. Mots-clés : Two  variable-density  jets;  digital  particle  image  velocimetry  technique;  separated  jet Résumé : Mixing of two variable-density jets, one of which is essentially a negatively buoyant jet (He) and the other a nonbuoyant jet (O2) is studied experimentally using digital particle image velocimetry technique for separated nozzle geometry. Two jets are separated from each other, i.e., He jet exit plane is located upstream of the O2 jet exit plane. Experiments were carried out keeping the nonbuoyant O2 jet at constant Reynolds number (Re2=245) and varying the Richardson number (Ri1=1.8,4.7,16.4) of the buoyant He jet. The interaction between two jets as a function of buoyancy strength of helium jet is investigated. The flow visualization images clearly demonstrate the growth and shape of buoyant jet as a function of Richardson number. Mean velocity and vorticity field results provide quantitative picture about the mixing and interaction between the two jets. The stream trace results show the flow structures, i.e., recirculation zone and foci of vortex structures as a function of Richardson number. The mixing between two jets takes place at far downstream region for low Richardson number (Ri1=1.8). At high Richardson number (Ri1=16.4), the buoyant He jet is located near its exit plane without any direct interaction with the O2 jet. At the intermediate Richardson number (Ri1=4.7), the buoyant jet encroaches the nonbuoyant O2 jet at a favorable penetration distance and a good amount of mixing between the two jets take place. The jet growth results based on the y0.5-location development in the streamwise direction clearly demonstrate the interaction between the He and O2 jets in the interjet region. The entrainment coefficient, vorticity magnitude, and turbulent kinetic energy magnitude are maximum at the intermediate Richardson number (Ri1=4.7) demonstrating direct relationship among each other. The mixing between buoyant He jet and nonbuoyant O2 jet is a function of both shear between the two jets and the strength of buoyant plume. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/Issue.aspx?issueID=27337 [...]

Experimental investigation of flow past a square cylinder at an angle of incidence / Sushanta Dutta in Journal of engineering mechanics, Vol. 134 n°9 (Septembre 2008) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 134 n°9 (Septembre 2008) . - pp.788–803. Titre : Experimental investigation of flow past a square cylinder at an angle of incidence Type de document : texte imprimé Auteurs : Sushanta Dutta, Auteur ; P. K. Panigrahi, Auteur ; K. Muralidhar, Auteur Année de publication : 2008 Article en page(s) : pp.788–803. Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Cylinders  Drag  Coefficients  Experimentation Résumé : Flow past a square cylinder placed at an angle to the incoming flow is experimentally investigated using particle image velocimetry, hot wire anemometry, and flow visualization. The Reynolds number based on cylinder size and the average incoming velocity is set equal to 410. Data for four cylinder orientations ( θ=0 , 22.5, 30, and 45°) and two aspect ratios [ AR=16 and 28] are reported. Results are presented in terms of drag coefficient, Strouhal number, time averaged velocity, stream traces, turbulence intensity, power spectra, and vorticity field. In addition, flow visualization images in the near wake of the cylinder are discussed. The shape and size of the recirculation bubble downstream of the cylinder are strong functions of orientation. A minimum in drag coefficient and maximum in Strouhal number is observed at a cylinder orientation of 22.5°. The v -velocity profile and time-average stream traces show that the wake and the separation process are asymmetric at orientations of 22.5 and 30°. The corresponding power spectra show additional peaks related to secondary vortical structures that arise from nonlinear interaction between the Karman vortices. The flow visualization images show the streamwise separation distance between the alternating vortices to be a function of cylinder orientation. Further, the flow approaches three dimensionality early, i.e., closer to the cylinder surface for the 22.5° orientation. The drag coefficient decreases with an increase in aspect ratio, while the Strouhal number is seen to increase with aspect ratio. The turbulence intensity is higher for the large aspect ratio cylinder and the maximum turbulence intensity appears at an earlier streamwise location. The overall dependence of drag coefficient and Strouhal number on orientation is preserved for the two aspect ratios studied. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282008%29134%3A9%2878 [...] [article] Experimental investigation of flow past a square cylinder at an angle of incidence [texte imprimé] / Sushanta Dutta, Auteur ; P. K. Panigrahi, Auteur ; K. Muralidhar, Auteur . - 2008 . - pp.788–803. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 134 n°9 (Septembre 2008) . - pp.788–803. Mots-clés : Cylinders  Drag  Coefficients  Experimentation Résumé : Flow past a square cylinder placed at an angle to the incoming flow is experimentally investigated using particle image velocimetry, hot wire anemometry, and flow visualization. The Reynolds number based on cylinder size and the average incoming velocity is set equal to 410. Data for four cylinder orientations ( θ=0 , 22.5, 30, and 45°) and two aspect ratios [ AR=16 and 28] are reported. Results are presented in terms of drag coefficient, Strouhal number, time averaged velocity, stream traces, turbulence intensity, power spectra, and vorticity field. In addition, flow visualization images in the near wake of the cylinder are discussed. The shape and size of the recirculation bubble downstream of the cylinder are strong functions of orientation. A minimum in drag coefficient and maximum in Strouhal number is observed at a cylinder orientation of 22.5°. The v -velocity profile and time-average stream traces show that the wake and the separation process are asymmetric at orientations of 22.5 and 30°. The corresponding power spectra show additional peaks related to secondary vortical structures that arise from nonlinear interaction between the Karman vortices. The flow visualization images show the streamwise separation distance between the alternating vortices to be a function of cylinder orientation. Further, the flow approaches three dimensionality early, i.e., closer to the cylinder surface for the 22.5° orientation. The drag coefficient decreases with an increase in aspect ratio, while the Strouhal number is seen to increase with aspect ratio. The turbulence intensity is higher for the large aspect ratio cylinder and the maximum turbulence intensity appears at an earlier streamwise location. The overall dependence of drag coefficient and Strouhal number on orientation is preserved for the two aspect ratios studied. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282008%29134%3A9%2878 [...]

PIV investigation of flow behind surface mounted detached square cylinder / P. K. Panigrahi in Transactions of the ASME . Journal of fluids engineering, Vol. 131 N° 1 (Janvier 2009) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 1 (Janvier 2009) . - 16 p. Titre : PIV investigation of flow behind surface mounted detached square cylinder Type de document : texte imprimé Auteurs : P. K. Panigrahi, Auteur Année de publication : 2009 Article en page(s) : 16 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : field  behind  surface;  particle  image  velocimetry;  square  cylinder Résumé : The flow field behind surface mounted detached square ribs under the approaching flat plate turbulent boundary layer has been experimentally studied using the particle image velocimetry (PIV) (two-component and stereo) technique in both streamwise and cross stream measurement planes. An oil film visualization study has been carried out for correlating the surface flow patterns to the flow structures. The Reynolds number based on the rib height is equal to 11,075. The ratio of the gap height to the square rib size is set equal to 0.2, 0.37, 0.57, and 1.0. The ratio of approaching boundary layer thickness to rib height is equal to 0.2. The mean and rms velocity fields, streamwise and spanwise vorticity fields, velocity gradient and velocity vector fields, turbulent kinetic energy budgets, and stream trace results are reported. The second invariant of the velocity gradient tensor results are presented to distinguish between the rotational and shear contribution of the vorticity field. The recirculation bubbles with a focilike structure are observed behind the detached ribs. These structures are displaced upward, i.e., away from the wall surface with an increase in gap size of the detached cylinder. The size of the recirculation bubble also drops with an increase in the gap size. The stream traces in the cross stream plane show node-saddle patterns, whose near wall concentration is high for a lower gap size detached cylinder. The oil film visualization images show saddle patterns at the meeting point between the flow through the gap and the reattaching shear layer for the lower gap size detached cylinder. The v-velocity magnitude distribution shows greater wall-normal motion across the wake for the detached cylinder of lower gap size. There is a significant near wall velocity fluctuation for the lower gap size detached cylinder. The higher velocity fluctuation due to the near wall flow structures contributes toward an increase in the near wall mixing of a detached cylinder geometry. Overall, the present study clearly demonstrates the flow structures behind detached ribs, which are responsible for effective near wall mixing. The results from this study provide useful understanding for the design of turbulators in various practical applications. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] PIV investigation of flow behind surface mounted detached square cylinder [texte imprimé] / P. K. Panigrahi, Auteur . - 2009 . - 16 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 1 (Janvier 2009) . - 16 p. Mots-clés : field  behind  surface;  particle  image  velocimetry;  square  cylinder Résumé : The flow field behind surface mounted detached square ribs under the approaching flat plate turbulent boundary layer has been experimentally studied using the particle image velocimetry (PIV) (two-component and stereo) technique in both streamwise and cross stream measurement planes. An oil film visualization study has been carried out for correlating the surface flow patterns to the flow structures. The Reynolds number based on the rib height is equal to 11,075. The ratio of the gap height to the square rib size is set equal to 0.2, 0.37, 0.57, and 1.0. The ratio of approaching boundary layer thickness to rib height is equal to 0.2. The mean and rms velocity fields, streamwise and spanwise vorticity fields, velocity gradient and velocity vector fields, turbulent kinetic energy budgets, and stream trace results are reported. The second invariant of the velocity gradient tensor results are presented to distinguish between the rotational and shear contribution of the vorticity field. The recirculation bubbles with a focilike structure are observed behind the detached ribs. These structures are displaced upward, i.e., away from the wall surface with an increase in gap size of the detached cylinder. The size of the recirculation bubble also drops with an increase in the gap size. The stream traces in the cross stream plane show node-saddle patterns, whose near wall concentration is high for a lower gap size detached cylinder. The oil film visualization images show saddle patterns at the meeting point between the flow through the gap and the reattaching shear layer for the lower gap size detached cylinder. The v-velocity magnitude distribution shows greater wall-normal motion across the wake for the detached cylinder of lower gap size. There is a significant near wall velocity fluctuation for the lower gap size detached cylinder. The higher velocity fluctuation due to the near wall flow structures contributes toward an increase in the near wall mixing of a detached cylinder geometry. Overall, the present study clearly demonstrates the flow structures behind detached ribs, which are responsible for effective near wall mixing. The results from this study provide useful understanding for the design of turbulators in various practical applications. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]