Modelling and simulations are conducted on velocity slip and interfacial momentum transfer for supersonic two-pha.se (gas-droplet) flow in the transient section inside and outside a Laval jet(LJ). The initial velocity...Modelling and simulations are conducted on velocity slip and interfacial momentum transfer for supersonic two-pha.se (gas-droplet) flow in the transient section inside and outside a Laval jet(LJ). The initial velocity slip between gas and droplets causes an interfacial momentum transfer flux as high as (2.0-5.0) x 104 Pa. The relaxation time corresponding to this transient process is in the range of 0.015-0.090ms for the two-phase flow formed inside the LJ and less than 0.5ms outside the LJ. It demonstrates the unique performance of this system for application to fast chemical reactions using electrically active media with a lifetime in the order of 1 ms. Through the simulations of the transient processes with initial Mach number Mg from 2.783 to 4.194 at different axial positions inside the LJ, it is found that Mg has the strongest effect on the process. The momentum flux increases as the Mach number decreases. Due to compression by the shock wave at the end of the LJ, the flow pattern becomes two dimensional and viscous outside the LJ. Laser Doppler velocirneter (LDV) measurements of droplet velocities outside the LJ are in reasonably good agreement with the results of the simulation.展开更多
The two-dimensional turbulent evaporating gas-droplet two-phase flows in an afterburner diffusor of turbo-fan jet engines are simulated by the k-ε turbulence model and the particle trajectory model. Comparison of pre...The two-dimensional turbulent evaporating gas-droplet two-phase flows in an afterburner diffusor of turbo-fan jet engines are simulated by the k-ε turbulence model and the particle trajectory model. Comparison of predicted gas velocity and temperature distributions with experimental results for the cases without liquid spray shows pretty good agreement. Gas-droplet two-phase flow predictions give plausible droplet trajectories, fuel-vapor concentration distribution, gas-phase velocity and temperature field in presence of liquid droplets. One run of computation with this method is made for a particular afterburner. The results indicate that the location of the atomizers is not favorable to flame stabilization and combustion efficiency. The proposed numerical modeling can also be adopted for optimization design and performance evaluation of afterburner combustors of turbo-fan jet engines.展开更多
Spray evaporation of liquid fuels in a turbulent flow is a common process in various engineering applications such as combustion.Interactions between fuel droplets(discrete phase)and fluid flow(continuous phase)have a...Spray evaporation of liquid fuels in a turbulent flow is a common process in various engineering applications such as combustion.Interactions between fuel droplets(discrete phase)and fluid flow(continuous phase)have a considerable effect on liquid fuel evaporation.In this paper,both the single-and two-phase modeling of liquid fuel injection into a model evaporating chamber are presented.The influences of important issues such as turbulence models,coupling between gas phase and droplets,secondary break-up and air swirling on the current spray simulation are investigated.Accordingly,the shear stress transport turbulence model,Taylor analogy break-up and two-way coupling models are applied to simulate the two-phase flow.Atomization and spray of fuel droplets in hot air are modeled employing an Eulerian-Lagrangian approach.The current results show an acceptable agreement with the experiments.Adjacent the fuel atomizer,bigger droplets are detected near the spray edge and minor droplets are situated in the middle.With increasing the droplets axial position,the droplets diameter decreases with a finite slope.The smaller droplets have a deeper penetration,but their lifetime is smaller and they evaporate sooner.A linear relation between penetration and lifetime of smaller droplets is detected.Maximum droplet penetration and mean axial velocity of gas phase are observed for no air swirling case.The effect of variation of swirl number on the lifetime of droplets is almost negligible.By enhancing the swirl number,the uniformity of droplet size distribution is reduced and some large droplets are formed up in the domain.展开更多
基金Supported by the National Natural Science Foundation of China (No. 29876022) and Grant of State Key Laboratory of High Speed Hydrodynamics (No. 2007).
文摘Modelling and simulations are conducted on velocity slip and interfacial momentum transfer for supersonic two-pha.se (gas-droplet) flow in the transient section inside and outside a Laval jet(LJ). The initial velocity slip between gas and droplets causes an interfacial momentum transfer flux as high as (2.0-5.0) x 104 Pa. The relaxation time corresponding to this transient process is in the range of 0.015-0.090ms for the two-phase flow formed inside the LJ and less than 0.5ms outside the LJ. It demonstrates the unique performance of this system for application to fast chemical reactions using electrically active media with a lifetime in the order of 1 ms. Through the simulations of the transient processes with initial Mach number Mg from 2.783 to 4.194 at different axial positions inside the LJ, it is found that Mg has the strongest effect on the process. The momentum flux increases as the Mach number decreases. Due to compression by the shock wave at the end of the LJ, the flow pattern becomes two dimensional and viscous outside the LJ. Laser Doppler velocirneter (LDV) measurements of droplet velocities outside the LJ are in reasonably good agreement with the results of the simulation.
文摘The two-dimensional turbulent evaporating gas-droplet two-phase flows in an afterburner diffusor of turbo-fan jet engines are simulated by the k-ε turbulence model and the particle trajectory model. Comparison of predicted gas velocity and temperature distributions with experimental results for the cases without liquid spray shows pretty good agreement. Gas-droplet two-phase flow predictions give plausible droplet trajectories, fuel-vapor concentration distribution, gas-phase velocity and temperature field in presence of liquid droplets. One run of computation with this method is made for a particular afterburner. The results indicate that the location of the atomizers is not favorable to flame stabilization and combustion efficiency. The proposed numerical modeling can also be adopted for optimization design and performance evaluation of afterburner combustors of turbo-fan jet engines.
文摘Spray evaporation of liquid fuels in a turbulent flow is a common process in various engineering applications such as combustion.Interactions between fuel droplets(discrete phase)and fluid flow(continuous phase)have a considerable effect on liquid fuel evaporation.In this paper,both the single-and two-phase modeling of liquid fuel injection into a model evaporating chamber are presented.The influences of important issues such as turbulence models,coupling between gas phase and droplets,secondary break-up and air swirling on the current spray simulation are investigated.Accordingly,the shear stress transport turbulence model,Taylor analogy break-up and two-way coupling models are applied to simulate the two-phase flow.Atomization and spray of fuel droplets in hot air are modeled employing an Eulerian-Lagrangian approach.The current results show an acceptable agreement with the experiments.Adjacent the fuel atomizer,bigger droplets are detected near the spray edge and minor droplets are situated in the middle.With increasing the droplets axial position,the droplets diameter decreases with a finite slope.The smaller droplets have a deeper penetration,but their lifetime is smaller and they evaporate sooner.A linear relation between penetration and lifetime of smaller droplets is detected.Maximum droplet penetration and mean axial velocity of gas phase are observed for no air swirling case.The effect of variation of swirl number on the lifetime of droplets is almost negligible.By enhancing the swirl number,the uniformity of droplet size distribution is reduced and some large droplets are formed up in the domain.
