This paper, using the dataset of BBFs （bursty bulk flows） observed by two Cluster satellites C1 and C4, studies the difference between onset times of BBFs observed by C1 and C4. It is found that the onset time diffe...This paper, using the dataset of BBFs （bursty bulk flows） observed by two Cluster satellites C1 and C4, studies the difference between onset times of BBFs observed by C1 and C4. It is found that the onset time differences of most of BBFs observed by Cl and C4 are smaller than 60 s. The average onset time difference of BBFs of CI and C4 is 68.5 s. The probabilities of onset time difference of BBFs of C1 and C4 larger than 30, 60, 90 and 120 s are respectively 55%, 35%, 27% and 23%. The largest onset time difference of BBFs of C1 and C4 decreases with the increase of earthward component of maximum velocities of BBFs. The onset time difference of BBFs of C1 and C4 results from the velocity inhomogeneity inside the flow channel of BBF, which may be produced in propagation path and/or in source region of BBFs. Such a wide range of onset time difference of BBFs suggests that the velocity inhomogeneity inside the flow channel of BBF is various. These results are very important to the current study of substorm research based on THEMIS data because they indicate that it is impossible to determine the onset time of BBF with a single satellite.展开更多
Experimental and numerical studies were carried out to evaluate the effect of vortex generator on a small cylindrical protrusion at Mach number 2.0. The experiments were performed using the supersonic blow down wind t...Experimental and numerical studies were carried out to evaluate the effect of vortex generator on a small cylindrical protrusion at Mach number 2.0. The experiments were performed using the supersonic blow down wind tunnel on different heights of cylindrical protrusion with vortex generator placed ahead of them. The upstream and downstream flow around the cylindrical protrusion is influenced by vortex generator as is observed using both visualization and pressure measurement techniques. Numerical studies using three dimensional steady implicit formulations with standard k-ω turbulence model was performed. Results obtained through the present computation are compared with the experimental results at Mach 2.0. Good agreements between computation and experimental results have been achieved. The results indicate that the aerodynamic drag acting on cylindrical protrusion can be reduced by adopting vortex generator.展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos. 40931054 and 41174141)National Basic Research Program of China ("973" Program) (Grant No. 2011CB811404)
文摘This paper, using the dataset of BBFs （bursty bulk flows） observed by two Cluster satellites C1 and C4, studies the difference between onset times of BBFs observed by C1 and C4. It is found that the onset time differences of most of BBFs observed by Cl and C4 are smaller than 60 s. The average onset time difference of BBFs of CI and C4 is 68.5 s. The probabilities of onset time difference of BBFs of C1 and C4 larger than 30, 60, 90 and 120 s are respectively 55%, 35%, 27% and 23%. The largest onset time difference of BBFs of C1 and C4 decreases with the increase of earthward component of maximum velocities of BBFs. The onset time difference of BBFs of C1 and C4 results from the velocity inhomogeneity inside the flow channel of BBF, which may be produced in propagation path and/or in source region of BBFs. Such a wide range of onset time difference of BBFs suggests that the velocity inhomogeneity inside the flow channel of BBF is various. These results are very important to the current study of substorm research based on THEMIS data because they indicate that it is impossible to determine the onset time of BBF with a single satellite.
基金supported by Advanced Research Center Program(NRF-2013R1A5A1073861) through the National Research Foundation of Korea(NRF) grant funded by the Korea government(MSIP) contracted through Advanced Space Propulsion Research Center at Seoul National University.(Project Number: 0659-20140012)
文摘Experimental and numerical studies were carried out to evaluate the effect of vortex generator on a small cylindrical protrusion at Mach number 2.0. The experiments were performed using the supersonic blow down wind tunnel on different heights of cylindrical protrusion with vortex generator placed ahead of them. The upstream and downstream flow around the cylindrical protrusion is influenced by vortex generator as is observed using both visualization and pressure measurement techniques. Numerical studies using three dimensional steady implicit formulations with standard k-ω turbulence model was performed. Results obtained through the present computation are compared with the experimental results at Mach 2.0. Good agreements between computation and experimental results have been achieved. The results indicate that the aerodynamic drag acting on cylindrical protrusion can be reduced by adopting vortex generator.
