Swirling addition to the stream is beneficial for the fluid mixing.This work aims to study the mixing process intensification in a conventional T-jets mixer by the swirling addition.After experimental verification by ...Swirling addition to the stream is beneficial for the fluid mixing.This work aims to study the mixing process intensification in a conventional T-jets mixer by the swirling addition.After experimental verification by the planar laser-induced fluorescence technique,large eddy simulation with the dynamic kinetic energy sub-grid stress model is used to predict how the swirling strength(in terms of swirling number,S_(w))and swirling directions affect the mixing performance,e.g.the tracer concentration distribution,mixing time,and turbulent characteristics in the T-jets mixers,Predictions show that the swirling strength is the key factor affecting the mixing efficiency of the process.The overall mixing time,τ_(90),can be significantly reduced by increasing S_(w).Vortex analysis shows that more turbulent eddies appear in the collision zone and the turbulent kinetic energy dissipation rate increases obviously with the swirling addition.When S_(w) is kept constant,the mixing process can be accelerated and intensified by adding swirling to only one stream,to both streams with the opposite swirling directions,or to both streams with the same swirling directions.Amplification of the mixing process by enlarging the mixer size or increasing the flow rates is also optimized.Thus,this work provides a new strategy to improve the mixing performance of the traditional T-jets mixers by the swirling addition.展开更多
Jet characteristics of air supply opening in a ventilating or anair-conditioning system is primarily decided by the folw state in the duct connected to the opening.It is valuable to study the opening jet characteristi...Jet characteristics of air supply opening in a ventilating or anair-conditioning system is primarily decided by the folw state in the duct connected to the opening.It is valuable to study the opening jet characteristics and the flow state in a duct. In thisstudy, the Large Eddy Simulation (LES) technique combined with the Tarlor-Galerkin Finite ElementMethod (FEM) in Computational Fluid Dynamics (CFD) was applied to the problem. The 3-D flow fieldsin ducts around air supply opening under typical conditions were investigated by numericalsimulation as well as experimental measurements. Numerical results agree well with the availableexperimental data. It indicates that the LES method is available under the conditions withcomplicated boundaries and inner accompanied by anisotropic large-scale eddies, and it is credibleto predict the jet deflection characteristics around an opening.展开更多
A nonqinear eddy viscosity model （NLEVM） and a scalable hybrid Reynolds averaged Navier-Stokes/large eddy simula- tion （RANS/LES） strategy are developed to improve the capability of the eddy viscosity model （EVM...A nonqinear eddy viscosity model （NLEVM） and a scalable hybrid Reynolds averaged Navier-Stokes/large eddy simula- tion （RANS/LES） strategy are developed to improve the capability of the eddy viscosity model （EVM） to simulate complex flows featuring separations and unsteady motions. To study the performance of the NLEVM, numerical simulations around S809 airfoil are carried out and the results show that the NLEVM performs much better when a large separation occurs. Calculated results of the flow around a triangular cylinder show that the NLEVM can improve the precision of the flow fields to some extents, but the error is still considerable, and the small turbulence structures can not be clearly captured as the EVM. Whereas the scalable hybrid RANS/LES model based on the NLEVM is fairy effective on resolving the turbulent structures and can give more satisfactory predictions of the flow fields.展开更多
基金the financial support from the National Natural Science Foundation of China(22078058)。
文摘Swirling addition to the stream is beneficial for the fluid mixing.This work aims to study the mixing process intensification in a conventional T-jets mixer by the swirling addition.After experimental verification by the planar laser-induced fluorescence technique,large eddy simulation with the dynamic kinetic energy sub-grid stress model is used to predict how the swirling strength(in terms of swirling number,S_(w))and swirling directions affect the mixing performance,e.g.the tracer concentration distribution,mixing time,and turbulent characteristics in the T-jets mixers,Predictions show that the swirling strength is the key factor affecting the mixing efficiency of the process.The overall mixing time,τ_(90),can be significantly reduced by increasing S_(w).Vortex analysis shows that more turbulent eddies appear in the collision zone and the turbulent kinetic energy dissipation rate increases obviously with the swirling addition.When S_(w) is kept constant,the mixing process can be accelerated and intensified by adding swirling to only one stream,to both streams with the opposite swirling directions,or to both streams with the same swirling directions.Amplification of the mixing process by enlarging the mixer size or increasing the flow rates is also optimized.Thus,this work provides a new strategy to improve the mixing performance of the traditional T-jets mixers by the swirling addition.
文摘Jet characteristics of air supply opening in a ventilating or anair-conditioning system is primarily decided by the folw state in the duct connected to the opening.It is valuable to study the opening jet characteristics and the flow state in a duct. In thisstudy, the Large Eddy Simulation (LES) technique combined with the Tarlor-Galerkin Finite ElementMethod (FEM) in Computational Fluid Dynamics (CFD) was applied to the problem. The 3-D flow fieldsin ducts around air supply opening under typical conditions were investigated by numericalsimulation as well as experimental measurements. Numerical results agree well with the availableexperimental data. It indicates that the LES method is available under the conditions withcomplicated boundaries and inner accompanied by anisotropic large-scale eddies, and it is credibleto predict the jet deflection characteristics around an opening.
基金Project supported by the National Natural Science Foun-dation of China(Grant Nos.51179100,51279184)
文摘A nonqinear eddy viscosity model （NLEVM） and a scalable hybrid Reynolds averaged Navier-Stokes/large eddy simula- tion （RANS/LES） strategy are developed to improve the capability of the eddy viscosity model （EVM） to simulate complex flows featuring separations and unsteady motions. To study the performance of the NLEVM, numerical simulations around S809 airfoil are carried out and the results show that the NLEVM performs much better when a large separation occurs. Calculated results of the flow around a triangular cylinder show that the NLEVM can improve the precision of the flow fields to some extents, but the error is still considerable, and the small turbulence structures can not be clearly captured as the EVM. Whereas the scalable hybrid RANS/LES model based on the NLEVM is fairy effective on resolving the turbulent structures and can give more satisfactory predictions of the flow fields.
