A bionic experimental platform was designed for the purpose of investigating time accurate three-dimensional flow field, using digital particle image velocimetry （DSPIV）. The wake behind the flapping trail of a robo...A bionic experimental platform was designed for the purpose of investigating time accurate three-dimensional flow field, using digital particle image velocimetry （DSPIV）. The wake behind the flapping trail of a robotic fish model was studied at high spatial resolution. The study was performed in a water channel. A robot fish model was designed and built. The model was fixed onto a rigid support frame- work using a cable-supporting method, with twelve stretched wires. The entire tail of the model can perform prescribed motions in two degrees of freedom, mainly in carangiform mode, by driving its afterbody and lunate caudal fin respectively. The DSPIV system was set up to operate in a trans- lational manner, measuring velocity field in a series of parallel slices. Phase locked measurements were repeated for a number of runs, allowing reconstruction of phase average flow field. Vortex structures with phase history of the wake were obtained. The study reveals some new and complex three-dimensional flow structures in the wake of the fish, including ＂reverse hairpin vortex＂ and ＂reverse Karman S-H vortex rings＂, allowing insight into physics of this complex flow.展开更多
Viscous heating has a substantial influence on the extrusion forming process and product quality of powder materials.This study selected the MUZL420 ring die pellet mill as the research object,from which a 3D flow phy...Viscous heating has a substantial influence on the extrusion forming process and product quality of powder materials.This study selected the MUZL420 ring die pellet mill as the research object,from which a 3D flow physical model was established.The numerical simulation of 3D nonisothermal flow in the extrusion pelletizing process of granulated alfalfa was performed with POLYFLOW.The distribution laws of pressure,velocity,shear rate,viscosity,viscous heating and temperature in the flow field were revealed to thoroughly investigate the pelletizing process and provide a reference for structural optimization and process control.The results showed that two extrusion zones in the pelleting chamber were symmetrical with respect to the center,and the significant pressure gradient along the rotating direction of the ring die and the roller caused the material to flow back in the opposite direction.There were larger velocity gradients,shear rates and viscous heating levels in the deformation and compaction zone,the negative pressure zone behind the extrusion zone and the die holes.The distribution of viscosity was opposite to that of the shear rate.The temperature increase area caused by viscous heating gradually expanded from the material inlet to the bottom of the extrusion chamber along the Z-axis direction,and the temperature increased accordingly.The extrusion force and the forming temperature in the extrusion forming zone were captured in the numerical simulation.The extrusion forming density was calculated with the regression prediction model established through the simulation experiment of pelletizing with a ring die.Through a comparison with the results of mean alfalfa pellet density from the ring die pellet mill experiment,the relative error was less than 5%,which indicated that the numerical simulation method was reliable.展开更多
基金supported by the National Natural Science Foundation of China (10772017 and 10472011)BUAA-985 Foundation
文摘A bionic experimental platform was designed for the purpose of investigating time accurate three-dimensional flow field, using digital particle image velocimetry （DSPIV）. The wake behind the flapping trail of a robotic fish model was studied at high spatial resolution. The study was performed in a water channel. A robot fish model was designed and built. The model was fixed onto a rigid support frame- work using a cable-supporting method, with twelve stretched wires. The entire tail of the model can perform prescribed motions in two degrees of freedom, mainly in carangiform mode, by driving its afterbody and lunate caudal fin respectively. The DSPIV system was set up to operate in a trans- lational manner, measuring velocity field in a series of parallel slices. Phase locked measurements were repeated for a number of runs, allowing reconstruction of phase average flow field. Vortex structures with phase history of the wake were obtained. The study reveals some new and complex three-dimensional flow structures in the wake of the fish, including ＂reverse hairpin vortex＂ and ＂reverse Karman S-H vortex rings＂, allowing insight into physics of this complex flow.
基金funded by the National Natural Science Foundation of China(NSFC)(51365002)the Gansu Agricultural University Youth Tutor Foundation(GAUQNDS-201204).
文摘Viscous heating has a substantial influence on the extrusion forming process and product quality of powder materials.This study selected the MUZL420 ring die pellet mill as the research object,from which a 3D flow physical model was established.The numerical simulation of 3D nonisothermal flow in the extrusion pelletizing process of granulated alfalfa was performed with POLYFLOW.The distribution laws of pressure,velocity,shear rate,viscosity,viscous heating and temperature in the flow field were revealed to thoroughly investigate the pelletizing process and provide a reference for structural optimization and process control.The results showed that two extrusion zones in the pelleting chamber were symmetrical with respect to the center,and the significant pressure gradient along the rotating direction of the ring die and the roller caused the material to flow back in the opposite direction.There were larger velocity gradients,shear rates and viscous heating levels in the deformation and compaction zone,the negative pressure zone behind the extrusion zone and the die holes.The distribution of viscosity was opposite to that of the shear rate.The temperature increase area caused by viscous heating gradually expanded from the material inlet to the bottom of the extrusion chamber along the Z-axis direction,and the temperature increased accordingly.The extrusion force and the forming temperature in the extrusion forming zone were captured in the numerical simulation.The extrusion forming density was calculated with the regression prediction model established through the simulation experiment of pelletizing with a ring die.Through a comparison with the results of mean alfalfa pellet density from the ring die pellet mill experiment,the relative error was less than 5%,which indicated that the numerical simulation method was reliable.
