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Experimental and computational investigations to evaluate the effects of fluid viscosity and particle size on erosion damage / Risa Okita in Transactions of the ASME . Journal of fluids engineering, Vol. 134 N° 6 (Juin 2012) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 134 N° 6 (Juin 2012) . - 13 p. Titre : Experimental and computational investigations to evaluate the effects of fluid viscosity and particle size on erosion damage Type de document : texte imprimé Auteurs : Risa Okita, Auteur ; Yongli Zhang, Auteur ; Brenton S. McLaury, Auteur Année de publication : 2012 Article en page(s) : 13 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : erosion  modeling;  CFD;  viscosity;  prticle  size Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Zhang et al. (2006) utilized computational fluid dynamics (CFD) to examine the validity of erosion models that have been implemented into CFD codes to predict solid-particle erosion in air and water for inconel 625. This work is an extension of Zhang's work and is presented as a step toward obtaining a better understanding of the effects of fluid viscosity and sand-particle size on measured and calculated erosion ratios, where erosion ratio is defined as the ratio of mass loss of material to mass of solid particles. The erosion ratios of aluminum 6061-T6 were measured for direct impingement conditions of a submerged jet. Fluid viscosities of 1, 10, 25, and 50 cP and sand-particle sizes of 20, 150, and 300 µm were tested. The average fluid speed of the jet was maintained at 10 m/s. Erosion data show that erosion ratios for the 20- and 150-µm particles are reduced as the viscosity is increased, whereas, surprisingly, the erosion ratios for the 300-µm particles do not seem to change much for the higher viscosities. For all viscosities considered, larger particles produced higher erosion ratios, for the same mass of sand, than smaller particles. Concurrently, an erosion equation has been generated based on erosion testing of the same material in air. The new erosion model has been compared to available models and has been implemented into a commercially available CFD code to predict erosion ratios for a variety of flow conditions, flow geometries, and particle sizes. Because particle speed and impact angle greatly influence erosion ratios of the material, calculated particle speeds were compared with measurements. Comparisons reveal that, as the particles penetrate the near wall shear layer, particles in the higher viscosity liquids tend to slow down more rapidly than particles in the lower viscosity liquids. In addition, CFD predictions and particle-speed measurements are used to explain why the erosion data for larger particles is less sensitive to the increased viscosities. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JFEGA4000134000006 [...] [article] Experimental and computational investigations to evaluate the effects of fluid viscosity and particle size on erosion damage [texte imprimé] / Risa Okita, Auteur ; Yongli Zhang, Auteur ; Brenton S. McLaury, Auteur . - 2012 . - 13 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 134 N° 6 (Juin 2012) . - 13 p. Mots-clés : erosion  modeling;  CFD;  viscosity;  prticle  size Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : Zhang et al. (2006) utilized computational fluid dynamics (CFD) to examine the validity of erosion models that have been implemented into CFD codes to predict solid-particle erosion in air and water for inconel 625. This work is an extension of Zhang's work and is presented as a step toward obtaining a better understanding of the effects of fluid viscosity and sand-particle size on measured and calculated erosion ratios, where erosion ratio is defined as the ratio of mass loss of material to mass of solid particles. The erosion ratios of aluminum 6061-T6 were measured for direct impingement conditions of a submerged jet. Fluid viscosities of 1, 10, 25, and 50 cP and sand-particle sizes of 20, 150, and 300 µm were tested. The average fluid speed of the jet was maintained at 10 m/s. Erosion data show that erosion ratios for the 20- and 150-µm particles are reduced as the viscosity is increased, whereas, surprisingly, the erosion ratios for the 300-µm particles do not seem to change much for the higher viscosities. For all viscosities considered, larger particles produced higher erosion ratios, for the same mass of sand, than smaller particles. Concurrently, an erosion equation has been generated based on erosion testing of the same material in air. The new erosion model has been compared to available models and has been implemented into a commercially available CFD code to predict erosion ratios for a variety of flow conditions, flow geometries, and particle sizes. Because particle speed and impact angle greatly influence erosion ratios of the material, calculated particle speeds were compared with measurements. Comparisons reveal that, as the particles penetrate the near wall shear layer, particles in the higher viscosity liquids tend to slow down more rapidly than particles in the lower viscosity liquids. In addition, CFD predictions and particle-speed measurements are used to explain why the erosion data for larger particles is less sensitive to the increased viscosities. DEWEY : 620.1 ISSN : 0098-2202 En ligne : http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JFEGA4000134000006 [...]

Improvements of particle near-wall velocity and erosion predictions using a commercial CFD code / Yongli Zhang in Transactions of the ASME . Journal of fluids engineering, Vol. 131 N° 3 (Mars 2009) 

Public ISBD [article]  in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 3 (Mars 2009) . - 09 p. Titre : Improvements of particle near-wall velocity and erosion predictions using a commercial CFD code Type de document : texte imprimé Auteurs : Yongli Zhang, Auteur ; Brenton S. McLaury, Auteur ; Siamack A. Shirazi, Auteur Année de publication : 2009 Article en page(s) : 09 p. Note générale : fluids engineering Langues : Anglais (eng) Mots-clés : CFD  codes;  pipe  walls;  velocity;  near-wall  modifications Résumé : The determination of a representative particle impacting velocity is an important component in calculating solid particle erosion inside pipe geometry. Currently, most commercial computational fluid dynamics (CFD) codes allow the user to calculate particle trajectories using a Lagrangian approach. Additionally, the CFD codes calculate particle impact velocities with the pipe walls. However, these commercial CFD codes normally use a wall function to simulate the turbulent velocity field in the near-wall region. This wall-function velocity field near the wall can affect the small particle motion in the near-wall region. Furthermore, the CFD codes assume that particles have zero volume when particle impact information is being calculated. In this investigation, particle motions that are simulated using a commercially available CFD code are examined in the near-wall region. Calculated solid particle erosion patterns are compared with experimental data to investigate the accuracy of the models that are being used to calculate particle impacting velocities. While not considered in particle tracking routines in most CFD codes, the turbulent velocity profile in the near-wall region is taken into account in this investigation, and the effect on particle impact velocity is investigated. The simulation results show that the particle impact velocity is affected significantly when near-wall velocity profile is implemented. In addition, the effects of particle size are investigated in the near-wall region of a turbulent flow in a 90 deg sharp bend. A CFD code is modified to account for particle size effects in the near-wall region before and after the particle impact. It is found from the simulations that accounting for the rebound at the particle radius helps avoid nonphysical impacts and reduces the number of impacts by more than one order-of-magnitude for small particles (25 μm) due to turbulent velocity fluctuations. For large particles (256 μm), however, nonphysical impacts are not observed in the simulations. Solid particle erosion is predicted before and after introducing these modifications, and the results are compared with experimental data. It is shown that the near-wall modification and turbulent particle interactions significantly affect the simulation results. Modifications can significantly improve the current CFD-based solid particle erosion modeling. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...] [article] Improvements of particle near-wall velocity and erosion predictions using a commercial CFD code [texte imprimé] / Yongli Zhang, Auteur ; Brenton S. McLaury, Auteur ; Siamack A. Shirazi, Auteur . - 2009 . - 09 p. fluids engineering Langues : Anglais (eng) in Transactions of the ASME . Journal of fluids engineering > Vol. 131 N° 3 (Mars 2009) . - 09 p. Mots-clés : CFD  codes;  pipe  walls;  velocity;  near-wall  modifications Résumé : The determination of a representative particle impacting velocity is an important component in calculating solid particle erosion inside pipe geometry. Currently, most commercial computational fluid dynamics (CFD) codes allow the user to calculate particle trajectories using a Lagrangian approach. Additionally, the CFD codes calculate particle impact velocities with the pipe walls. However, these commercial CFD codes normally use a wall function to simulate the turbulent velocity field in the near-wall region. This wall-function velocity field near the wall can affect the small particle motion in the near-wall region. Furthermore, the CFD codes assume that particles have zero volume when particle impact information is being calculated. In this investigation, particle motions that are simulated using a commercially available CFD code are examined in the near-wall region. Calculated solid particle erosion patterns are compared with experimental data to investigate the accuracy of the models that are being used to calculate particle impacting velocities. While not considered in particle tracking routines in most CFD codes, the turbulent velocity profile in the near-wall region is taken into account in this investigation, and the effect on particle impact velocity is investigated. The simulation results show that the particle impact velocity is affected significantly when near-wall velocity profile is implemented. In addition, the effects of particle size are investigated in the near-wall region of a turbulent flow in a 90 deg sharp bend. A CFD code is modified to account for particle size effects in the near-wall region before and after the particle impact. It is found from the simulations that accounting for the rebound at the particle radius helps avoid nonphysical impacts and reduces the number of impacts by more than one order-of-magnitude for small particles (25 μm) due to turbulent velocity fluctuations. For large particles (256 μm), however, nonphysical impacts are not observed in the simulations. Solid particle erosion is predicted before and after introducing these modifications, and the results are compared with experimental data. It is shown that the near-wall modification and turbulent particle interactions significantly affect the simulation results. Modifications can significantly improve the current CFD-based solid particle erosion modeling. En ligne : http://fluidsengineering.asmedigitalcollection.asme.org/issue.aspx?journalid=122 [...]