Increasing velocity combined with decreasing mass of modern highspeed trains poses a question about the influence of strong crosswinds on its aerodynamics. Strong crosswinds may affect the running stability of high sp...Increasing velocity combined with decreasing mass of modern highspeed trains poses a question about the influence of strong crosswinds on its aerodynamics. Strong crosswinds may affect the running stability of high speed trains via the amplified aerodynamic forces and moments. In this study, a simulation of turbulent crosswind flows over the leading and end cars of ICE2 highspeed train was performed at different yaw angles in static and moving ground case scenarios. Since the train aerodynamic problems are closely associated with the flows occurring around train, the flow around the train was considered as incompressible and was obtained by solving the incom pressible form of the unsteady Reynoldsaveraged Navier Stokes （RANS） equations combined with the realizable kepsilon turbulence model. Important aerodynamic coef ficients such as the side force and rolling moment coeffi cients were calculated for yaw angles ranging from 30° to 60° and compared with the results obtained from wind tunnel test. The dependence of the flow structure on yaw angle was also presented. The nature of the flow field and its structure depicted by contours of velocity magnitude and streamline patterns along the train＇s crosssection were presented for different yaw angles. In addition, the pressure coefficient around the circumference of the train at dif ferent locations along its length was computed for yaw angles of 30° and 60°, The computed aerodynamic coef ficient outcomes using the realizable kepsilon turbulencemodel were in good agreement with the wind tunnel data. Both the side force coefficient and rolling moment coeffi cients increase steadily with yaw angle till about 50° before starting to exhibit an asymptotic behavior. Contours of velocity magnitude were also computed at different cross sections of the train along its length for different yaw angles. The result showed that magnitude of rotating vortex in the lee ward side increased with increasing yaw angle, which leads to the creation of a lowpressure region in the lee ward side of the train causing high side force and roll moment. Generally, this study shows that unsteady CFD RANS methods combined with an appropriate turbulence model can present an important means of assessing the crucial aerodynamic forces and moments of a highspeed train under strong crosswind conditions.展开更多
The rheological behavior of xanthan gum solutions is characterized using the HerschelBulkley model.Numerical simulations based on a laminar flow framework are conducted to investigate cavern evolution in non-Newtonian...The rheological behavior of xanthan gum solutions is characterized using the HerschelBulkley model.Numerical simulations based on a laminar flow framework are conducted to investigate cavern evolution in non-Newtonian fluids stirred by dual impellers under various operating conditions.The results indicate that fluid rheology has a limited influence on cavern shape and evolution.With increasing impeller speed,the flow field transitions from separated upper and lower caverns to a unified continuous structure.In the separated state,the heightto-diameter ratios of the caverns vary.Upon merging,the cavern initially extends axially toward the liquid surface and subsequently expands radially.When the cavern volume exceeds 90%of the tank volume,the system can be considered fully mobilized,effectively eliminating the cavern phenomenon.展开更多
文摘Increasing velocity combined with decreasing mass of modern highspeed trains poses a question about the influence of strong crosswinds on its aerodynamics. Strong crosswinds may affect the running stability of high speed trains via the amplified aerodynamic forces and moments. In this study, a simulation of turbulent crosswind flows over the leading and end cars of ICE2 highspeed train was performed at different yaw angles in static and moving ground case scenarios. Since the train aerodynamic problems are closely associated with the flows occurring around train, the flow around the train was considered as incompressible and was obtained by solving the incom pressible form of the unsteady Reynoldsaveraged Navier Stokes （RANS） equations combined with the realizable kepsilon turbulence model. Important aerodynamic coef ficients such as the side force and rolling moment coeffi cients were calculated for yaw angles ranging from 30° to 60° and compared with the results obtained from wind tunnel test. The dependence of the flow structure on yaw angle was also presented. The nature of the flow field and its structure depicted by contours of velocity magnitude and streamline patterns along the train＇s crosssection were presented for different yaw angles. In addition, the pressure coefficient around the circumference of the train at dif ferent locations along its length was computed for yaw angles of 30° and 60°, The computed aerodynamic coef ficient outcomes using the realizable kepsilon turbulencemodel were in good agreement with the wind tunnel data. Both the side force coefficient and rolling moment coeffi cients increase steadily with yaw angle till about 50° before starting to exhibit an asymptotic behavior. Contours of velocity magnitude were also computed at different cross sections of the train along its length for different yaw angles. The result showed that magnitude of rotating vortex in the lee ward side increased with increasing yaw angle, which leads to the creation of a lowpressure region in the lee ward side of the train causing high side force and roll moment. Generally, this study shows that unsteady CFD RANS methods combined with an appropriate turbulence model can present an important means of assessing the crucial aerodynamic forces and moments of a highspeed train under strong crosswind conditions.
基金supported by the National Natural Science Foundation of China(Grant No.52176040)the Natural Science Foundation of Shandong Province(Grant No.ZR2021ME161)the Science and Technology SMES Innovation Ability Improvement of Shandong Province(Grant No.2023TSGC0290).
文摘The rheological behavior of xanthan gum solutions is characterized using the HerschelBulkley model.Numerical simulations based on a laminar flow framework are conducted to investigate cavern evolution in non-Newtonian fluids stirred by dual impellers under various operating conditions.The results indicate that fluid rheology has a limited influence on cavern shape and evolution.With increasing impeller speed,the flow field transitions from separated upper and lower caverns to a unified continuous structure.In the separated state,the heightto-diameter ratios of the caverns vary.Upon merging,the cavern initially extends axially toward the liquid surface and subsequently expands radially.When the cavern volume exceeds 90%of the tank volume,the system can be considered fully mobilized,effectively eliminating the cavern phenomenon.
