Multistage centrifugal impellers with four different skew angles were investigated by using computational fluid dynamics.The purpose of this work is to investigate the influences of lean angle at the blade tip of the ...Multistage centrifugal impellers with four different skew angles were investigated by using computational fluid dynamics.The purpose of this work is to investigate the influences of lean angle at the blade tip of the impeller inlet.Four variations of lean angles,that is,8°,10°,15° and 20°,were made at first stage impeller.Reynolds Average Navier Stokes equation was used in simulation together with a shear?stress transport(SST) k-w turbulence model and mixing-plane approach,respectively.Three dimensional fluid flows were simplified using periodic model to reduce the computational cost and time required.A good performance was expected that the secondary flow can be effectively reduced in the flow passage of the impeller without excessive increase in manufacturing cost caused by the secondary flow.The results show that secondary flow affects the main flow intricately to form vortices or having non-uniform velocity in the flow passage,which in turn results in substantial fluid energy loss not only in the impeller but also in the guide vane downstream of impeller.The numerical solutions were performed and allowed the optimum design and operating conditions to be obtained.展开更多
Deformation behaviors of bicrystalline and nano-polycrystalline structures of various tilt angles and inclination angles in two dimensions are investigated in detail using a two-mode phase field crystal model.The inte...Deformation behaviors of bicrystalline and nano-polycrystalline structures of various tilt angles and inclination angles in two dimensions are investigated in detail using a two-mode phase field crystal model.The interaction between grain boundary(GB)and dislocation is also examined in bicrystals and nano-polycrystals that both contain asymmetric and symmetric tilt GBs,with energy analysis being carried out to analyze these processes.During deformation simulations,we assume the volume of each simulation cell at every time step is coincident with that of the initial state just before deformation.Our simulation results show that the behaviors of symmetric and asymmetric GBs in bicrystals and nano-polycrystals differ from each other depending on tilt angle and inclination angle.A new dislocation emission mechanism of interest is observed in bicrystals which contain low angle symmetric tilt GBs.Low angle GB has a higher mobility relative to high angle GB in both bicrystalline and nano-polycrystalline structures,as does asymmetric GB to symmetric GB.The generation,motion,pileup and annihilation of dislocations,grain rotation and grain coalescence are observed,which is consistent with the simulation results obtained by molecular dynamics.These simulation results can provide strong guidelines for experimentation.展开更多
基金Project(NRF-2010-013-D00007) supported by the National Research Foundation of KoreaWork finacially supported by the 2010 Research Professor Fund of Gyeongsang National University,Korea
文摘Multistage centrifugal impellers with four different skew angles were investigated by using computational fluid dynamics.The purpose of this work is to investigate the influences of lean angle at the blade tip of the impeller inlet.Four variations of lean angles,that is,8°,10°,15° and 20°,were made at first stage impeller.Reynolds Average Navier Stokes equation was used in simulation together with a shear?stress transport(SST) k-w turbulence model and mixing-plane approach,respectively.Three dimensional fluid flows were simplified using periodic model to reduce the computational cost and time required.A good performance was expected that the secondary flow can be effectively reduced in the flow passage of the impeller without excessive increase in manufacturing cost caused by the secondary flow.The results show that secondary flow affects the main flow intricately to form vortices or having non-uniform velocity in the flow passage,which in turn results in substantial fluid energy loss not only in the impeller but also in the guide vane downstream of impeller.The numerical solutions were performed and allowed the optimum design and operating conditions to be obtained.
基金supported by the National Natural Science Foundation of China(Grant Nos.51274167 and 51174168)the Northwestern Polytechnical University Foundation for the Fundamental Research(Grant No.JC20120222)
文摘Deformation behaviors of bicrystalline and nano-polycrystalline structures of various tilt angles and inclination angles in two dimensions are investigated in detail using a two-mode phase field crystal model.The interaction between grain boundary(GB)and dislocation is also examined in bicrystals and nano-polycrystals that both contain asymmetric and symmetric tilt GBs,with energy analysis being carried out to analyze these processes.During deformation simulations,we assume the volume of each simulation cell at every time step is coincident with that of the initial state just before deformation.Our simulation results show that the behaviors of symmetric and asymmetric GBs in bicrystals and nano-polycrystals differ from each other depending on tilt angle and inclination angle.A new dislocation emission mechanism of interest is observed in bicrystals which contain low angle symmetric tilt GBs.Low angle GB has a higher mobility relative to high angle GB in both bicrystalline and nano-polycrystalline structures,as does asymmetric GB to symmetric GB.The generation,motion,pileup and annihilation of dislocations,grain rotation and grain coalescence are observed,which is consistent with the simulation results obtained by molecular dynamics.These simulation results can provide strong guidelines for experimentation.
