An unsteady numerical simulation is conducted to examine the dynamic runback characteristics of a water film flow driven by a boundary layer airflow over a solid surface pertinent to the dynamic glaze ice accretion pr...An unsteady numerical simulation is conducted to examine the dynamic runback characteristics of a water film flow driven by a boundary layer airflow over a solid surface pertinent to the dynamic glaze ice accretion process over aircraft wing surfaces.The multiphase flow simulation results of the wind-driven water runback(WDWR)flow are compared quantitatively with the experimental results in terms of the time-dependent variations of the water film thickness profiles and evolution of the front contact point of the runback water film flow.The underlying mechanism of the intermittent water runback behavior is elucidated by analyzing the time evolution of the airflow velocity and vorticity fields above the runback water film flow over the solid surface.To the best knowledge of the authors,the work presented here is the first successful attempt to numerically examine the transient runback characteristics of WDWR flows.It serves as an excellent benchmark case for the development of best practices to model the important micro-physical processes responsible for the transient water transport over aircraft wing surfaces.展开更多
The metallurgical phenomena occurring in the continuous casting mold have a significant influence on the performance and the quality of steel product.The multiphase flow phenomena of molten steel,steel/slag interface ...The metallurgical phenomena occurring in the continuous casting mold have a significant influence on the performance and the quality of steel product.The multiphase flow phenomena of molten steel,steel/slag interface and gas bubbles in the slab continuous casting mold were described by numerical simulation,and the effect of electromagnetic brake（EMBR） and argon gas blowing on the process were investigated.The relationship between wavy fluctuation height near meniscus and the level fluctuation index F,which reflects the situation of mold flux entrapment,was clarified.Moreover,based on a microsegregation model of solute elements in mushy zone with δ/γ transformation and a thermo-mechanical coupling finite element model of shell solidification,the thermal and mechanical behaviors of solidifying shell including the dynamic distribution laws of air gap and mold flux,temperature and stress of shell in slab continuous casting mold were described.展开更多
Water-rich cracks represent common tunnel defects.Intense pressure waves generated by trains traveling through tunnels may undergo enhancement within water-rich cracks.Using the re-normalization group(RNG)k-εturbulen...Water-rich cracks represent common tunnel defects.Intense pressure waves generated by trains traveling through tunnels may undergo enhancement within water-rich cracks.Using the re-normalization group(RNG)k-εturbulence model and volume of fluid(VOF)method,this study analyzes the spatiotemporal distribution,spectral features,and influencing factors of pressure wave propagation in water-rich cracks when two high-speed trains intersect in a tunnel.The flow mechanisms underlying the pressure enhancement within water-rich cracks are also revealed.The main conclusions are as follows:1)The positive and negative peak pressure coefficients in water-rich cracks are 1.34 and-2.36,with corresponding pressure gradient peaks of 31.41 kPa/s and-34.01 kPa/s.Compared to the tunnel wall,the peak pressure coefficients and gradients exhibit increases of 34.41%/44.63%and 31.61%/60.46%,respectively.2)The dominant frequency of the pressure wave power spectral density(PSD)at the crack tip is 26.97%higher than that in the tunnel.The PSD peak value continuously increases with depth and is the largest at the crack tip,representing an increase of 9.36%compared to the tunnel.3)An increase in crack width reduces the peaks of pressure waves,pressure gradients,and PSD,while increases in vertical and transverse depths amplify these peaks.Crack width has the most significant impact on pressure waves and pressure gradients,while transverse depth has the most significant effect on PSD peak values.4)Driven by inertia and pressure differences,the water body oscillates variably,enhancing pressure fluctuation amplitude at the crack tip.The higher the water body's movement velocity,the greater the pressure gradient at the crack tip.The above research results may provide a reference for crack harnessing in high-speed railway tunnels.展开更多
A fluid dynamic model for a gas-solid circulating fluidized bed （CFB） designed using two coupled riser reactors is developed and implemented numerically with code programmed in Matlab. The fluid dynamic model contai...A fluid dynamic model for a gas-solid circulating fluidized bed （CFB） designed using two coupled riser reactors is developed and implemented numerically with code programmed in Matlab. The fluid dynamic model contains heat and species mass balances to calculate temperatures and compositions for a carbonation/calcination loop process. Because of the high computational costs required to resolve the three-dimensional phenomena, a model representing a trade-offbetween computational time requirements and accuracy is developed. For dynamic processes with a solid flux between the two reactor units that depends on the fluid dynamics of both risers, a dynamic one-dimensional two-fluid model is sufficient. A two-fluid model using the constant particle viscosity closure for the stress term is used for the solid phase, and an algebraic turbulence model is applied to the gas phase. The numerical model implementa- tion is based on the finite volume method with a staggered grid scheme. The exchange of solids between the reactor units constituting the circulating fluidized bed （solid flux） is implemented through additional mass source/sink terms in the continuity equations of the two phases, For model validation, a relevant experimental analysis provided in the literature is reproduced by the numerical simulations, The numerical analysis indicates that sufficient heat integration between the two reactor units is important for the performance of the circulating fluidized bed system, The two-fluid model performs fairly well for this chemical process operated in a CFB designed as two coupled riser reactors. Further analysis and optimization of the solution algorithms and the reactor coupling strategy is warranted.展开更多
基金supported by the National Science Foundation(NSF)of the USA(Grant Nos.TIP-2140489,CBET-2313310,and CBET-2415347).
文摘An unsteady numerical simulation is conducted to examine the dynamic runback characteristics of a water film flow driven by a boundary layer airflow over a solid surface pertinent to the dynamic glaze ice accretion process over aircraft wing surfaces.The multiphase flow simulation results of the wind-driven water runback(WDWR)flow are compared quantitatively with the experimental results in terms of the time-dependent variations of the water film thickness profiles and evolution of the front contact point of the runback water film flow.The underlying mechanism of the intermittent water runback behavior is elucidated by analyzing the time evolution of the airflow velocity and vorticity fields above the runback water film flow over the solid surface.To the best knowledge of the authors,the work presented here is the first successful attempt to numerically examine the transient runback characteristics of WDWR flows.It serves as an excellent benchmark case for the development of best practices to model the important micro-physical processes responsible for the transient water transport over aircraft wing surfaces.
基金Item Sponsored by National Outstanding Young Scientist Foundation of China(50925415)Fundamental Research Funds for Central Universities of China(N100102001)
文摘The metallurgical phenomena occurring in the continuous casting mold have a significant influence on the performance and the quality of steel product.The multiphase flow phenomena of molten steel,steel/slag interface and gas bubbles in the slab continuous casting mold were described by numerical simulation,and the effect of electromagnetic brake（EMBR） and argon gas blowing on the process were investigated.The relationship between wavy fluctuation height near meniscus and the level fluctuation index F,which reflects the situation of mold flux entrapment,was clarified.Moreover,based on a microsegregation model of solute elements in mushy zone with δ/γ transformation and a thermo-mechanical coupling finite element model of shell solidification,the thermal and mechanical behaviors of solidifying shell including the dynamic distribution laws of air gap and mold flux,temperature and stress of shell in slab continuous casting mold were described.
基金Project(51978670)supported by the National Natural Science Foundation of ChinaProject(N2024G018)supported by the Science and Technology Research and Development Program Project of China Railway+1 种基金Projects(Major Project:2021-Major-01 and 2023-Major-12Major Special Project:2021-Special-04-2)supported by the Science and Technology Research and Development Program Project of China Railway Group Limited。
文摘Water-rich cracks represent common tunnel defects.Intense pressure waves generated by trains traveling through tunnels may undergo enhancement within water-rich cracks.Using the re-normalization group(RNG)k-εturbulence model and volume of fluid(VOF)method,this study analyzes the spatiotemporal distribution,spectral features,and influencing factors of pressure wave propagation in water-rich cracks when two high-speed trains intersect in a tunnel.The flow mechanisms underlying the pressure enhancement within water-rich cracks are also revealed.The main conclusions are as follows:1)The positive and negative peak pressure coefficients in water-rich cracks are 1.34 and-2.36,with corresponding pressure gradient peaks of 31.41 kPa/s and-34.01 kPa/s.Compared to the tunnel wall,the peak pressure coefficients and gradients exhibit increases of 34.41%/44.63%and 31.61%/60.46%,respectively.2)The dominant frequency of the pressure wave power spectral density(PSD)at the crack tip is 26.97%higher than that in the tunnel.The PSD peak value continuously increases with depth and is the largest at the crack tip,representing an increase of 9.36%compared to the tunnel.3)An increase in crack width reduces the peaks of pressure waves,pressure gradients,and PSD,while increases in vertical and transverse depths amplify these peaks.Crack width has the most significant impact on pressure waves and pressure gradients,while transverse depth has the most significant effect on PSD peak values.4)Driven by inertia and pressure differences,the water body oscillates variably,enhancing pressure fluctuation amplitude at the crack tip.The higher the water body's movement velocity,the greater the pressure gradient at the crack tip.The above research results may provide a reference for crack harnessing in high-speed railway tunnels.
基金support from the BIGCCS Centre,performed under the Norwegian Research Program Centers for Environment-Friendly Energy Research(FME)
文摘A fluid dynamic model for a gas-solid circulating fluidized bed （CFB） designed using two coupled riser reactors is developed and implemented numerically with code programmed in Matlab. The fluid dynamic model contains heat and species mass balances to calculate temperatures and compositions for a carbonation/calcination loop process. Because of the high computational costs required to resolve the three-dimensional phenomena, a model representing a trade-offbetween computational time requirements and accuracy is developed. For dynamic processes with a solid flux between the two reactor units that depends on the fluid dynamics of both risers, a dynamic one-dimensional two-fluid model is sufficient. A two-fluid model using the constant particle viscosity closure for the stress term is used for the solid phase, and an algebraic turbulence model is applied to the gas phase. The numerical model implementa- tion is based on the finite volume method with a staggered grid scheme. The exchange of solids between the reactor units constituting the circulating fluidized bed （solid flux） is implemented through additional mass source/sink terms in the continuity equations of the two phases, For model validation, a relevant experimental analysis provided in the literature is reproduced by the numerical simulations, The numerical analysis indicates that sufficient heat integration between the two reactor units is important for the performance of the circulating fluidized bed system, The two-fluid model performs fairly well for this chemical process operated in a CFB designed as two coupled riser reactors. Further analysis and optimization of the solution algorithms and the reactor coupling strategy is warranted.
