Documents disponibles écrits par cet auteur

Efficiency improvement of centrifugal reverse pumps / Shahram Derakhshan in Transactions of the ASME . Journal of fluids engineering, Vol. 131 N° 2 (Fevrier 2009) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 2 (Fevrier 2009) . - 09 p. Titre : Efficiency improvement of centrifugal reverse pumps Type de document : texte imprimé Auteurs : Shahram Derakhshan, Auteur ; Bijan Mohammadi, Auteur ; Ahmad Nourbakhsh, Auteur Année de publication : 2009 Article en page(s) : 09 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : reverse  pumps;  turbines;  Navier–Stokes  flow  solver Résumé : Pumps as turbines have been successfully applied in a wide range of small hydrosites in the world. Since the overall efficiency of these machines is lower than the overall efficiency of conventional turbines, their application in larger hydrosites is not economical. Therefore, the efficiency improvement of reverse pumps is essential. In this study, by focusing on a pump impeller, the shape of blades was redesigned to reach a higher efficiency in turbine mode using a gradient based optimization algorithm coupled by a 3D Navier–Stokes flow solver. Also, another modification was done by rounding the blades’ leading edges and hub/shroud interface in turbine mode. After each modification, a new impeller was manufactured and tested in the test rig. The efficiency was improved in all measured points by the optimal design of the blade and additional modification as the rounding of the blade’s profile in the impeller inlet and hub/shroud inlet edges in turbine mode. Experimental results confirmed the numerical efficiency improvement in all measured points. This study illustrated that the efficiency of the pump in reverse operation can be improved just by impeller modification. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Efficiency improvement of centrifugal reverse pumps [texte imprimé] / Shahram Derakhshan, Auteur ; Bijan Mohammadi, Auteur ; Ahmad Nourbakhsh, Auteur . - 2009 . - 09 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 2 (Fevrier 2009) . - 09 p. Mots-clés : reverse  pumps;  turbines;  Navier–Stokes  flow  solver Résumé : Pumps as turbines have been successfully applied in a wide range of small hydrosites in the world. Since the overall efficiency of these machines is lower than the overall efficiency of conventional turbines, their application in larger hydrosites is not economical. Therefore, the efficiency improvement of reverse pumps is essential. In this study, by focusing on a pump impeller, the shape of blades was redesigned to reach a higher efficiency in turbine mode using a gradient based optimization algorithm coupled by a 3D Navier–Stokes flow solver. Also, another modification was done by rounding the blades’ leading edges and hub/shroud interface in turbine mode. After each modification, a new impeller was manufactured and tested in the test rig. The efficiency was improved in all measured points by the optimal design of the blade and additional modification as the rounding of the blade’s profile in the impeller inlet and hub/shroud inlet edges in turbine mode. Experimental results confirmed the numerical efficiency improvement in all measured points. This study illustrated that the efficiency of the pump in reverse operation can be improved just by impeller modification. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]

Unsteady turbulent pipe flow due to water hammer using k-ω turbulence model / Alireza Riasi in Journal of hydraulic research, Vol. 47 N° 4 (2009) 

Public ISBD [article]  in Journal of hydraulic research > Vol. 47 N° 4 (2009) . - pp. 429-437 Titre : Unsteady turbulent pipe flow due to water hammer using k-ω turbulence model Titre original : Calcul de l'écoulement instationnaire en conduite dû à un coup de bélier avec le modèle de turbulence k-ω Type de document : texte imprimé Auteurs : Alireza Riasi, Auteur ; Ahmad Nourbakhsh, Auteur ; Mehrdad Raisee, Auteur Article en page(s) : pp. 429-437 Note générale : Hydraulique Langues : Anglais (eng) Mots-clés : Re-laminarization  Runge  scheme  Turbulence  Unsteady  pipe  flow  Water  hammer 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 : The behaviour of unsteady turbulent pipe flow resulting from water hammer is herein numerically studied. An accurate k-ω turbulence model for two-dimensional boundary layers under adverse and favorable pressure gradients (Wilcox 1994) was applied. The results of the numerical method are in good agreement with test data obtained from both steady and unsteady turbulent pipe flows. Also, the behaviour and the structure of turbulence in unsteady turbulent pipe flows caused by water hammer were investigated. A non-dimensional parameter P as the time scale ratio of turbulence diffusion in the radial direction to the pressure wave speed introduced by Ghidaoui et al. (2002) was used. The results show that for P≈1, the turbulence structure is significantly changed in the first cycle of water hammer, which is important for water quality modeling, whereas these variations are small for P>>1. Le comportement de l'écoulement turbulent instationnaire en conduite résultant d'un coup de bélier est étudié ici numériquement. Un modèle précis de turbulence k-ω pour les couches limites bidimensionnelles sous des gradients de pression contraires et favorables (Wilcox 1994) a été appliqué. Les résultats de la méthode numérique sont en bon accord avec les données expérimentales obtenues dans des écoulements turbulents stationnaires et instationnaires en conduite. On a étudié en outre, le comportement et la structure de la turbulence dans le cas où les écoulements turbulents instationnaires en conduite sont provoqués par un coup de bélier. On utilise un paramètre adimensionnel P introduit par Ghidaoui et al. (2002), rapport de l'échelle de temps de la diffusion radiale de la turbulence à la vitesse de l'onde de pression. Les résultats montrent que pour P ≈ 1, la structure de la turbulence est nettement modifiée dans le premier cycle du coup de bélier, ce qui est important pour les modèles de qualité de l'eau, tandis que ces variations sont faibles pour P » 1. DEWEY : 627 ISSN : 0022-1686 En ligne : http://www.journalhydraulicresearch.com [article] Unsteady turbulent pipe flow due to water hammer using k-ω turbulence model = Calcul de l'écoulement instationnaire en conduite dû à un coup de bélier avec le modèle de turbulence k-ω [texte imprimé] / Alireza Riasi, Auteur ; Ahmad Nourbakhsh, Auteur ; Mehrdad Raisee, Auteur . - pp. 429-437. Hydraulique Langues : Anglais (eng) in Journal of hydraulic research > Vol. 47 N° 4 (2009) . - pp. 429-437 Mots-clés : Re-laminarization  Runge  scheme  Turbulence  Unsteady  pipe  flow  Water  hammer 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 : The behaviour of unsteady turbulent pipe flow resulting from water hammer is herein numerically studied. An accurate k-ω turbulence model for two-dimensional boundary layers under adverse and favorable pressure gradients (Wilcox 1994) was applied. The results of the numerical method are in good agreement with test data obtained from both steady and unsteady turbulent pipe flows. Also, the behaviour and the structure of turbulence in unsteady turbulent pipe flows caused by water hammer were investigated. A non-dimensional parameter P as the time scale ratio of turbulence diffusion in the radial direction to the pressure wave speed introduced by Ghidaoui et al. (2002) was used. The results show that for P≈1, the turbulence structure is significantly changed in the first cycle of water hammer, which is important for water quality modeling, whereas these variations are small for P>>1. Le comportement de l'écoulement turbulent instationnaire en conduite résultant d'un coup de bélier est étudié ici numériquement. Un modèle précis de turbulence k-ω pour les couches limites bidimensionnelles sous des gradients de pression contraires et favorables (Wilcox 1994) a été appliqué. Les résultats de la méthode numérique sont en bon accord avec les données expérimentales obtenues dans des écoulements turbulents stationnaires et instationnaires en conduite. On a étudié en outre, le comportement et la structure de la turbulence dans le cas où les écoulements turbulents instationnaires en conduite sont provoqués par un coup de bélier. On utilise un paramètre adimensionnel P introduit par Ghidaoui et al. (2002), rapport de l'échelle de temps de la diffusion radiale de la turbulence à la vitesse de l'onde de pression. Les résultats montrent que pour P ≈ 1, la structure de la turbulence est nettement modifiée dans le premier cycle du coup de bélier, ce qui est important pour les modèles de qualité de l'eau, tandis que ces variations sont faibles pour P » 1. DEWEY : 627 ISSN : 0022-1686 En ligne : http://www.journalhydraulicresearch.com

Unsteady velocity profiles in laminar and turbulent water hammer flows / Alireza Riasi in Transactions of the ASME . Journal of fluids engineering, Vol. 131 N° 12 (Décembre 2009) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 12 (Décembre 2009) . - 08 p. Titre : Unsteady velocity profiles in laminar and turbulent water hammer flows Type de document : texte imprimé Auteurs : Alireza Riasi, Auteur ; Ahmad Nourbakhsh, Auteur ; Mehrdad Raisee, Auteur Année de publication : 2010 Article en page(s) : 08 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : flow  (dynamics);  turbulence;  water  hammer;  pipes;  waves;  shear  (mechanics);  equations;  pressure  gradient;  stress Résumé : The behavior of unsteady velocity profiles in laminar and turbulent water hammer flows is numerically investigated. In this way, the governing equations for the quasitwo-dimensional equations of transient flow in pipe are solved by using the modified implicit characteristics method. A k-ω turbulence model which is accurate for two-dimensional boundary layers under adverse and favorable pressure gradients is applied. The numerical results for both steady and unsteady turbulent pipe flows are in good agreement with the experimental data. The results indicate that both decelerating and accelerating flows are produced in a wave cycle of water hammer. During deceleration of the flow, a region of reverse flows and also strong gradients is formed near to the pipe wall. In case of the turbulent water hammer, this region is very close to the pipe wall compared with the laminar water hammer. Moreover, point of inflection and also point of zero velocity are formed in the unsteady velocity profile due to the water hammer problem. The results show that the point of zero velocity does not move very far from its initial location, while the point of inflection moves rapidly from the wall. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Unsteady velocity profiles in laminar and turbulent water hammer flows [texte imprimé] / Alireza Riasi, Auteur ; Ahmad Nourbakhsh, Auteur ; Mehrdad Raisee, Auteur . - 2010 . - 08 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 12 (Décembre 2009) . - 08 p. Mots-clés : flow  (dynamics);  turbulence;  water  hammer;  pipes;  waves;  shear  (mechanics);  equations;  pressure  gradient;  stress Résumé : The behavior of unsteady velocity profiles in laminar and turbulent water hammer flows is numerically investigated. In this way, the governing equations for the quasitwo-dimensional equations of transient flow in pipe are solved by using the modified implicit characteristics method. A k-ω turbulence model which is accurate for two-dimensional boundary layers under adverse and favorable pressure gradients is applied. The numerical results for both steady and unsteady turbulent pipe flows are in good agreement with the experimental data. The results indicate that both decelerating and accelerating flows are produced in a wave cycle of water hammer. During deceleration of the flow, a region of reverse flows and also strong gradients is formed near to the pipe wall. In case of the turbulent water hammer, this region is very close to the pipe wall compared with the laminar water hammer. Moreover, point of inflection and also point of zero velocity are formed in the unsteady velocity profile due to the water hammer problem. The results show that the point of zero velocity does not move very far from its initial location, while the point of inflection moves rapidly from the wall. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]