The Experts below are selected from a list of 327 Experts worldwide ranked by ideXlab platform
Philippe R. Spalart - One of the best experts on this subject based on the ideXlab platform.
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extensions of the spalart allmaras turbulence model to account for wall roughness
International Journal of Heat and Fluid Flow, 2003Co-Authors: B. Aupoix, Philippe R. SpalartAbstract:Abstract This paper describes extensions of the Spalart–Allmaras model to surface roughness, developed independently by Boeing and ONERA. They are rather simple and numerically benign, yield similar predictions, and are in fair agreement with experiments. They do not provide a description of the flow near the roughness elements, but rely instead on the “equivalent Sand Grain” approach. In that sense, they are not self-contained. The uncertain accuracy of the separate correlations, such as Dirling’s, needed to determine the Sand Grain size presents a challenge, as always. The roughness height must be much smaller than the boundary layer thickness, but the full range of roughness Reynolds number is covered. Some test cases reveal an incompatibility between the predicted effect of roughness on heat transfer and on skin friction. i.e. if the Sand Grain size is adjusted for skin friction, the heat transfer is too high.
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EXTENSIONS OF THE SPALART–ALLMARAS TURBULENCE MODEL TO ACCOUNT FOR WALL ROUGHNESS
Engineering Turbulence Modelling and Experiments 5, 2002Co-Authors: B. Aupoix, Philippe R. SpalartAbstract:This paper describes extensions of the Spalart–Allmaras model to surface roughness, developed independently by Boeing and ONERA. They are rather simple and numerically benign, yield similar predictions, and are in fair agreement with experiments. They do not provide a description of the flow near the roughness elements, but rely instead on the “equivalent Sand Grain” approach. In that sense, they are not self-contained. The uncertain accuracy of the separate correlations, such as Dirling’s, needed to determine the Sand Grain size presents a challenge, as always. The roughness height must be much smaller than the boundary layer thickness, but the full range of roughness Reynolds number is covered. Some test cases reveal an incompatibility between the predicted effect of roughness on heat transfer and on skin friction. i.e. if the Sand Grain size is adjusted for skin friction, the heat transfer is too high.
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extensions of the spalart allmaras turbulence model to account for wall roughness
Engineering Turbulence Modelling and Experiments 5#R##N#Proceedings of the 5th International Symposium on Engineering Turbulence Modelling and Measure, 2002Co-Authors: B. Aupoix, Philippe R. SpalartAbstract:Extensions of the Spalart–Allmaras turbulence model to account for wall roughness were developed independently by Boeing and ONERA. They are rather simple, yield similar predictions, and are in fair agreement with experiments. Tests confirm the weakness of the “equivalent Sand Grain” approach, i.e. the uncertain accuracy of correlations to determine the Sand-Grain size. Some test cases reveal an incompatibility between the predicted effect of roughness on heat transfer and on skin friction, i.e., if the Sand-Grain size is adjusted for skin friction, the heat transfer will be too high.
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EXTENSIONS OF THE SPALART–ALLMARAS TURBULENCE MODEL TO ACCOUNT FOR WALL ROUGHNESS
Engineering Turbulence Modelling and Experiments 5, 2002Co-Authors: B. Aupoix, Philippe R. SpalartAbstract:Extensions of the Spalart–Allmaras turbulence model to account for wall roughness were developed independently by Boeing and ONERA. They are rather simple, yield similar predictions, and are in fair agreement with experiments. Tests confirm the weakness of the “equivalent Sand Grain” approach, i.e. the uncertain accuracy of correlations to determine the Sand-Grain size. Some test cases reveal an incompatibility between the predicted effect of roughness on heat transfer and on skin friction, i.e., if the Sand-Grain size is adjusted for skin friction, the heat transfer will be too high.
B. Aupoix - One of the best experts on this subject based on the ideXlab platform.
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Improved heat transfer predictions on rough surfaces
International Journal of Heat and Fluid Flow, 2015Co-Authors: B. AupoixAbstract:Abstract The equivalent Sand Grain approach is the only approach to account for wall roughness in industrial CFD. As roughness effects are reproduced via a modification of the turbulence model in the wall region, the roughness correction preserves the Reynolds analogy. However, wall roughness increases much more the drag than the wall heat flux, so that the wall heat flux is overestimated with the equivalent Sand Grain approach. Due to the relative lack of detailed experimental data, the discrete element approach, which accounts for the different dynamical and thermal behaviours of wall roughness, was used to generate a large database to investigate thermal roughness effects. It turns out that, besides the equivalent Sand Grain height, another parameter has to be introduced to characterize roughness thermal effects. A correction of the turbulent Prandtl number was derived from the database and can be coupled to any roughness correction developed using ONERA’s technique. The thermal correction was validated for a wide range of roughness geometries, including academic roughness, in-service turbine blades and vanes and different ice shapes, for reduced equivalent Sand Grain heights k s + ranging from 10 to 6000, and for flows with pressure gradient. Heat transfer predictions are significantly improved, although heat transfer is generally still slightly overpredicted.
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extensions of the spalart allmaras turbulence model to account for wall roughness
International Journal of Heat and Fluid Flow, 2003Co-Authors: B. Aupoix, Philippe R. SpalartAbstract:Abstract This paper describes extensions of the Spalart–Allmaras model to surface roughness, developed independently by Boeing and ONERA. They are rather simple and numerically benign, yield similar predictions, and are in fair agreement with experiments. They do not provide a description of the flow near the roughness elements, but rely instead on the “equivalent Sand Grain” approach. In that sense, they are not self-contained. The uncertain accuracy of the separate correlations, such as Dirling’s, needed to determine the Sand Grain size presents a challenge, as always. The roughness height must be much smaller than the boundary layer thickness, but the full range of roughness Reynolds number is covered. Some test cases reveal an incompatibility between the predicted effect of roughness on heat transfer and on skin friction. i.e. if the Sand Grain size is adjusted for skin friction, the heat transfer is too high.
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EXTENSIONS OF THE SPALART–ALLMARAS TURBULENCE MODEL TO ACCOUNT FOR WALL ROUGHNESS
Engineering Turbulence Modelling and Experiments 5, 2002Co-Authors: B. Aupoix, Philippe R. SpalartAbstract:This paper describes extensions of the Spalart–Allmaras model to surface roughness, developed independently by Boeing and ONERA. They are rather simple and numerically benign, yield similar predictions, and are in fair agreement with experiments. They do not provide a description of the flow near the roughness elements, but rely instead on the “equivalent Sand Grain” approach. In that sense, they are not self-contained. The uncertain accuracy of the separate correlations, such as Dirling’s, needed to determine the Sand Grain size presents a challenge, as always. The roughness height must be much smaller than the boundary layer thickness, but the full range of roughness Reynolds number is covered. Some test cases reveal an incompatibility between the predicted effect of roughness on heat transfer and on skin friction. i.e. if the Sand Grain size is adjusted for skin friction, the heat transfer is too high.
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extensions of the spalart allmaras turbulence model to account for wall roughness
Engineering Turbulence Modelling and Experiments 5#R##N#Proceedings of the 5th International Symposium on Engineering Turbulence Modelling and Measure, 2002Co-Authors: B. Aupoix, Philippe R. SpalartAbstract:Extensions of the Spalart–Allmaras turbulence model to account for wall roughness were developed independently by Boeing and ONERA. They are rather simple, yield similar predictions, and are in fair agreement with experiments. Tests confirm the weakness of the “equivalent Sand Grain” approach, i.e. the uncertain accuracy of correlations to determine the Sand-Grain size. Some test cases reveal an incompatibility between the predicted effect of roughness on heat transfer and on skin friction, i.e., if the Sand-Grain size is adjusted for skin friction, the heat transfer will be too high.
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EXTENSIONS OF THE SPALART–ALLMARAS TURBULENCE MODEL TO ACCOUNT FOR WALL ROUGHNESS
Engineering Turbulence Modelling and Experiments 5, 2002Co-Authors: B. Aupoix, Philippe R. SpalartAbstract:Extensions of the Spalart–Allmaras turbulence model to account for wall roughness were developed independently by Boeing and ONERA. They are rather simple, yield similar predictions, and are in fair agreement with experiments. Tests confirm the weakness of the “equivalent Sand Grain” approach, i.e. the uncertain accuracy of correlations to determine the Sand-Grain size. Some test cases reveal an incompatibility between the predicted effect of roughness on heat transfer and on skin friction, i.e., if the Sand-Grain size is adjusted for skin friction, the heat transfer will be too high.
Jonathan Simm - One of the best experts on this subject based on the ideXlab platform.
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ICCS - Multiscale modelling in real-time flood forecasting systems: From Sand Grain to dike failure and inundation
Procedia Computer Science, 2010Co-Authors: Ben Gouldby, Valeria V. Krzhizhanovskaya, Jonathan SimmAbstract:Abstract Severe events around the globe have highlighted the threat to life, infrastructure and the environment posed by flooding. Flood forecasting systems are a vital component of broader flood risk management activities. These systems are becoming increasingly more sophisticated as their importance in reducing life loss and economic damages is realized. Part of this increase in complexity is focused on the ability to predict and warn of failures in dykes, levees and embankments. A new European ICT project, UrbanFlood for Environmental Services and Climate Change Adaptation, has recently been commissioned and is introduced in this presentation. The primary objective of the Urban Flood project is to develop early warning systems that will monitor flood protection systems in real-time, identify vulnerable locations, model the failure and predict dike collapse and subsequent inundation. In combination with the damage assessment, Urban Flood will serve as an advanced decision support system, mitigating the impact of seasonal and catastrophic floods. Modeling is one of the key tasks in the project. The models will be required to simulate the behavior of the material properties of the layered dikes (Sand, clay, peat, grass or concrete cover, metal frame, dam gates, etc.), during extreme hydraulic loading events. In earthen dikes, extra challenge is posed by the non-linear elastic plastic properties of the deformable clay. A realistic simulation of the dike will model the free-surface water dynamics; convective and diffusive transfer of water inside the porous materials; dynamic response of clay to the water pressure; structural mechanics, deformation and actual dike breakdown and flood. The models shall cover a wide range of scales from a Sand Grain to a flooded city. The time scales will range from seconds (for water penetrating the soil) to hours (for dike collapse dynamics and ocean tides). Eventually, the models will predict the influence of seasonal and global changes on the stability of flood defense systems. Full 3D transient simulation of dike failure with subsequent inundation will require significant computing resources. The project started three months ago, and we will present the plan for developing the modeling cascade for the system. This work is supported by the UrbanFlood European Union project N 248767, theme ICT-2009.6.4
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multiscale modelling in real time flood forecasting systems from Sand Grain to dike failure and inundation
International Conference on Conceptual Structures, 2010Co-Authors: Ben Gouldby, Valeria V. Krzhizhanovskaya, Jonathan SimmAbstract:Abstract Severe events around the globe have highlighted the threat to life, infrastructure and the environment posed by flooding. Flood forecasting systems are a vital component of broader flood risk management activities. These systems are becoming increasingly more sophisticated as their importance in reducing life loss and economic damages is realized. Part of this increase in complexity is focused on the ability to predict and warn of failures in dykes, levees and embankments. A new European ICT project, UrbanFlood for Environmental Services and Climate Change Adaptation, has recently been commissioned and is introduced in this presentation. The primary objective of the Urban Flood project is to develop early warning systems that will monitor flood protection systems in real-time, identify vulnerable locations, model the failure and predict dike collapse and subsequent inundation. In combination with the damage assessment, Urban Flood will serve as an advanced decision support system, mitigating the impact of seasonal and catastrophic floods. Modeling is one of the key tasks in the project. The models will be required to simulate the behavior of the material properties of the layered dikes (Sand, clay, peat, grass or concrete cover, metal frame, dam gates, etc.), during extreme hydraulic loading events. In earthen dikes, extra challenge is posed by the non-linear elastic plastic properties of the deformable clay. A realistic simulation of the dike will model the free-surface water dynamics; convective and diffusive transfer of water inside the porous materials; dynamic response of clay to the water pressure; structural mechanics, deformation and actual dike breakdown and flood. The models shall cover a wide range of scales from a Sand Grain to a flooded city. The time scales will range from seconds (for water penetrating the soil) to hours (for dike collapse dynamics and ocean tides). Eventually, the models will predict the influence of seasonal and global changes on the stability of flood defense systems. Full 3D transient simulation of dike failure with subsequent inundation will require significant computing resources. The project started three months ago, and we will present the plan for developing the modeling cascade for the system. This work is supported by the UrbanFlood European Union project N 248767, theme ICT-2009.6.4
Xiaojing Zheng - One of the best experts on this subject based on the ideXlab platform.
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The influence of wind velocity and Sand Grain diameter on the falling velocities of Sand particles
Powder Technology, 2013Co-Authors: Xiaojing Zheng, Shao-zhen Duan, Yi-rui LiangAbstract:Abstract In this paper, Sand velocities near the Sand bed in aeolian Sand transport were measured in a wind tunnel through an improved experimental scheme of the Particle Image Velocimetry (PIV) system and a data processing method. The influences of wind velocity and Sand Grain diameter on the probability distribution of the falling velocities of Sand particles were investigated. Results demonstrate that wind velocity and Sand Grain diameter have no obvious influence on the distribution pattern of the falling velocities of Sand particles, i.e., the probability distributions of the horizontal and vertical falling velocities of Sand particles follow a Gaussian distribution and a negative exponential distribution respectively, but wind velocity has an influence on the center, width and amplitude of the probability distribution of the horizontal falling velocities of Sand particles, as well as the decay constant and amplitude of the probability distribution of the vertical falling velocities of Sand particles. Eventually, we presented formulas to describe the probability distribution of the falling velocities of Sand particles with regard to the influence of wind velocity.
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A three‐dimensional analysis on lift‐off velocities of Sand Grains in wind‐blown Sand flux
Earth Surface Processes and Landforms, 2008Co-Authors: Xiaojing Zheng, Ning Cheng, Li XieAbstract:This paper focuses on a key problem in wind-blown Sand transport research, the lift-off velocities of Sand Grains. A three-dimensional Grain-bed collision model comprising an impact Sand Grain, a creeping Sand Grain and a sustaining Grain is presented. Based on this model, the analytical formulae of Sand Grains' linear and angular velocities are derived. The rebound/ejected coefficient (ratio of rebound/ejected velocity to impact velocity) and angle are numerically calculated using the analytical formulae and they agree well with the experiment results, which indicates that the three-dimensional model is credible and necessary. Comparisons of our results with the results gained by a two-dimensional Grain-bed collision model show that all components of both rebound and ejected velocities gained by the three-dimensional model are lower than the corresponding ones done by two-dimensional model apart from the horizontal rebound velocity. It also shows the lateral velocity and the lateral angular velocity, as well as the upward angular velocity, cannot be obtained by a two-dimensional model, and cannot be ignored when the impact velocity is high. Copyright © 2008 John Wiley & Sons, Ltd.
Valeria V. Krzhizhanovskaya - One of the best experts on this subject based on the ideXlab platform.
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ICCS - Multiscale modelling in real-time flood forecasting systems: From Sand Grain to dike failure and inundation
Procedia Computer Science, 2010Co-Authors: Ben Gouldby, Valeria V. Krzhizhanovskaya, Jonathan SimmAbstract:Abstract Severe events around the globe have highlighted the threat to life, infrastructure and the environment posed by flooding. Flood forecasting systems are a vital component of broader flood risk management activities. These systems are becoming increasingly more sophisticated as their importance in reducing life loss and economic damages is realized. Part of this increase in complexity is focused on the ability to predict and warn of failures in dykes, levees and embankments. A new European ICT project, UrbanFlood for Environmental Services and Climate Change Adaptation, has recently been commissioned and is introduced in this presentation. The primary objective of the Urban Flood project is to develop early warning systems that will monitor flood protection systems in real-time, identify vulnerable locations, model the failure and predict dike collapse and subsequent inundation. In combination with the damage assessment, Urban Flood will serve as an advanced decision support system, mitigating the impact of seasonal and catastrophic floods. Modeling is one of the key tasks in the project. The models will be required to simulate the behavior of the material properties of the layered dikes (Sand, clay, peat, grass or concrete cover, metal frame, dam gates, etc.), during extreme hydraulic loading events. In earthen dikes, extra challenge is posed by the non-linear elastic plastic properties of the deformable clay. A realistic simulation of the dike will model the free-surface water dynamics; convective and diffusive transfer of water inside the porous materials; dynamic response of clay to the water pressure; structural mechanics, deformation and actual dike breakdown and flood. The models shall cover a wide range of scales from a Sand Grain to a flooded city. The time scales will range from seconds (for water penetrating the soil) to hours (for dike collapse dynamics and ocean tides). Eventually, the models will predict the influence of seasonal and global changes on the stability of flood defense systems. Full 3D transient simulation of dike failure with subsequent inundation will require significant computing resources. The project started three months ago, and we will present the plan for developing the modeling cascade for the system. This work is supported by the UrbanFlood European Union project N 248767, theme ICT-2009.6.4
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multiscale modelling in real time flood forecasting systems from Sand Grain to dike failure and inundation
International Conference on Conceptual Structures, 2010Co-Authors: Ben Gouldby, Valeria V. Krzhizhanovskaya, Jonathan SimmAbstract:Abstract Severe events around the globe have highlighted the threat to life, infrastructure and the environment posed by flooding. Flood forecasting systems are a vital component of broader flood risk management activities. These systems are becoming increasingly more sophisticated as their importance in reducing life loss and economic damages is realized. Part of this increase in complexity is focused on the ability to predict and warn of failures in dykes, levees and embankments. A new European ICT project, UrbanFlood for Environmental Services and Climate Change Adaptation, has recently been commissioned and is introduced in this presentation. The primary objective of the Urban Flood project is to develop early warning systems that will monitor flood protection systems in real-time, identify vulnerable locations, model the failure and predict dike collapse and subsequent inundation. In combination with the damage assessment, Urban Flood will serve as an advanced decision support system, mitigating the impact of seasonal and catastrophic floods. Modeling is one of the key tasks in the project. The models will be required to simulate the behavior of the material properties of the layered dikes (Sand, clay, peat, grass or concrete cover, metal frame, dam gates, etc.), during extreme hydraulic loading events. In earthen dikes, extra challenge is posed by the non-linear elastic plastic properties of the deformable clay. A realistic simulation of the dike will model the free-surface water dynamics; convective and diffusive transfer of water inside the porous materials; dynamic response of clay to the water pressure; structural mechanics, deformation and actual dike breakdown and flood. The models shall cover a wide range of scales from a Sand Grain to a flooded city. The time scales will range from seconds (for water penetrating the soil) to hours (for dike collapse dynamics and ocean tides). Eventually, the models will predict the influence of seasonal and global changes on the stability of flood defense systems. Full 3D transient simulation of dike failure with subsequent inundation will require significant computing resources. The project started three months ago, and we will present the plan for developing the modeling cascade for the system. This work is supported by the UrbanFlood European Union project N 248767, theme ICT-2009.6.4
