This research aims to simulate a gravity flow fractionation—the process to fractionate erythrocytes through gravitational field using ANSYS simulation software. A particular microfluidic channel was designed as a sep...This research aims to simulate a gravity flow fractionation—the process to fractionate erythrocytes through gravitational field using ANSYS simulation software. A particular microfluidic channel was designed as a separation device. The gravitational equilibrium conditions of the erythrocytes and gravitational field as the parameters were chosen, then deriving the erythrocytes’ path through numerical simulations. After the actual analog measurements, there is no big difference between the flow velocity and the pressure under +/–10% atmosphere condition. According to the simulation results, the particle with the size 8 μm (similar to the erythrocyte size) can be separated to the outside channel and discharged from the collecting area, other particles with the size 9 μm will stay in the fluid motion and can be collected in the final collection area for preservation. Through the analog analysis by using the software-ANSYS-Fluent, the complete flowing path of the particles and the feasibility of the Gravity-Flow Fractionation can be directly proven.展开更多
Gaseous detonation propagating in a toroidal chamber was numerically studied for hydrogen/oxygen/nitrogen mixtures. The numerical method used is based on the three-dimensional Euler equations with detailed finiterate ...Gaseous detonation propagating in a toroidal chamber was numerically studied for hydrogen/oxygen/nitrogen mixtures. The numerical method used is based on the three-dimensional Euler equations with detailed finiterate chemistry. The results show that the calculated streak picture is in qualitative agreement with the picture recorded by a high speed streak camera from published literature. The three-dimensional flow field induced by a continuously rotating detonation was visualized and distinctive features of the rotating detonations were clearly depicted. Owing to the unconfined character of detonation wavelet, a deficit of detonation parameters was observed. Due to the effects of wall geometries, the strength of the outside detonation front is stronger than that of the inside portion. The detonation thus propagates with a constant circular velocity. Numerical simulation also shows three-dimensional rotating detonation structures, which display specific feature of the detonation- shock combined wave. Discrete burning gas pockets are formed due to instability of the discontinuity. It is believed that the present study could give an insight into the interest- ing properties of the continuously rotating detonation, and is thus beneficial to the design of continuous detonation propulsion systems.展开更多
This paper presents an analytical solution to periodical streaming potential, flow-induced electric field and velocity of periodical pressure-driven flows in twodimensional uniform microchannel based on the Poisson-Bo...This paper presents an analytical solution to periodical streaming potential, flow-induced electric field and velocity of periodical pressure-driven flows in twodimensional uniform microchannel based on the Poisson-Boltzmann equations for electric double layer and Navier-Stokes equation for liquid flow. Dimensional analysis indicates that electric-viscous force depends on three factors： （1） Electric-viscous number representing a ratio between maximum of electric-viscous force and pressure gradient in a steady state, （2） profile function describing the distribution profile of electro-viscous force in channel section, and （3） coupling coefficient reflecting behavior of arnplitude damping and phase offset of electro-viscous force. Analytical results indicate that flow-induced electric field and flow velocity depend on frequency Reynolds number （Re = wh^2/v）. Flow-induced electric field varies very slowly with Re when Re 〈 1, and rapidly decreases when Re 〉 1. Electro-viscous effect on flow-induced electric field and flow velocity are very significant when the rate of the channel width to the thickness of electric double layer is small.展开更多
The effects of out-of-plane shear flows on fast magnetic reconnection are numerically investigated by a two- dimensional （2D） hybrid model in an initial Harris sheet equilibrium with flows. The equilibrium and drive...The effects of out-of-plane shear flows on fast magnetic reconnection are numerically investigated by a two- dimensional （2D） hybrid model in an initial Harris sheet equilibrium with flows. The equilibrium and driven shear flows out of the 2D reconnection plane with symmetric and antisymmetric profiles respectively are used in the simulation. It is found that the out-of-plane flows with shears in-plane can change the quadrupolar structure of the out-of-plane magnetic field and, therefore, modify the growth rate of magnetic reconnection. Furthermore, the driven flow varying along the anti-parallel magnetic field can either enhance or reduce the reconnection rate as the direction of flow changes. Secondary islands are also generated in the process with converting the initial X-point into an O-point.展开更多
文摘This research aims to simulate a gravity flow fractionation—the process to fractionate erythrocytes through gravitational field using ANSYS simulation software. A particular microfluidic channel was designed as a separation device. The gravitational equilibrium conditions of the erythrocytes and gravitational field as the parameters were chosen, then deriving the erythrocytes’ path through numerical simulations. After the actual analog measurements, there is no big difference between the flow velocity and the pressure under +/–10% atmosphere condition. According to the simulation results, the particle with the size 8 μm (similar to the erythrocyte size) can be separated to the outside channel and discharged from the collecting area, other particles with the size 9 μm will stay in the fluid motion and can be collected in the final collection area for preservation. Through the analog analysis by using the software-ANSYS-Fluent, the complete flowing path of the particles and the feasibility of the Gravity-Flow Fractionation can be directly proven.
基金supported by the National Natural Science Foundation of China (10872096)the Open Fund of State Key Laboratory of Explosion Science and Technology, Beijing University of Science and Technology (KFJJ09-13)
文摘Gaseous detonation propagating in a toroidal chamber was numerically studied for hydrogen/oxygen/nitrogen mixtures. The numerical method used is based on the three-dimensional Euler equations with detailed finiterate chemistry. The results show that the calculated streak picture is in qualitative agreement with the picture recorded by a high speed streak camera from published literature. The three-dimensional flow field induced by a continuously rotating detonation was visualized and distinctive features of the rotating detonations were clearly depicted. Owing to the unconfined character of detonation wavelet, a deficit of detonation parameters was observed. Due to the effects of wall geometries, the strength of the outside detonation front is stronger than that of the inside portion. The detonation thus propagates with a constant circular velocity. Numerical simulation also shows three-dimensional rotating detonation structures, which display specific feature of the detonation- shock combined wave. Discrete burning gas pockets are formed due to instability of the discontinuity. It is believed that the present study could give an insight into the interest- ing properties of the continuously rotating detonation, and is thus beneficial to the design of continuous detonation propulsion systems.
基金Project supported by the National Natural Science Foundation of China (No.10472036)
文摘This paper presents an analytical solution to periodical streaming potential, flow-induced electric field and velocity of periodical pressure-driven flows in twodimensional uniform microchannel based on the Poisson-Boltzmann equations for electric double layer and Navier-Stokes equation for liquid flow. Dimensional analysis indicates that electric-viscous force depends on three factors： （1） Electric-viscous number representing a ratio between maximum of electric-viscous force and pressure gradient in a steady state, （2） profile function describing the distribution profile of electro-viscous force in channel section, and （3） coupling coefficient reflecting behavior of arnplitude damping and phase offset of electro-viscous force. Analytical results indicate that flow-induced electric field and flow velocity depend on frequency Reynolds number （Re = wh^2/v）. Flow-induced electric field varies very slowly with Re when Re 〈 1, and rapidly decreases when Re 〉 1. Electro-viscous effect on flow-induced electric field and flow velocity are very significant when the rate of the channel width to the thickness of electric double layer is small.
基金Project supported by the National Natural Science Foundation of China (Grant Nos.10935004,1126114032,10778613,10575018,40731056,10975012,and 11261140326)
文摘The effects of out-of-plane shear flows on fast magnetic reconnection are numerically investigated by a two- dimensional （2D） hybrid model in an initial Harris sheet equilibrium with flows. The equilibrium and driven shear flows out of the 2D reconnection plane with symmetric and antisymmetric profiles respectively are used in the simulation. It is found that the out-of-plane flows with shears in-plane can change the quadrupolar structure of the out-of-plane magnetic field and, therefore, modify the growth rate of magnetic reconnection. Furthermore, the driven flow varying along the anti-parallel magnetic field can either enhance or reduce the reconnection rate as the direction of flow changes. Secondary islands are also generated in the process with converting the initial X-point into an O-point.
