The aim of this work is to investigate the flow instabilities in a baffled, stirred tank generated by a single Rushton turbine by means of large eddy simulation （LES）. The sliding mesh method was used for the coupli...The aim of this work is to investigate the flow instabilities in a baffled, stirred tank generated by a single Rushton turbine by means of large eddy simulation （LES）. The sliding mesh method was used for the coupling between the rotating and the stationary frame of references. The calculations were carried out on the ＂Shengcao-21C＂ supercomputer using a computational fluid dynamics （CFD） code CFX5. The flow fields predicted by the LES simulation and the simulation using standard κ-ε model were compared to the results from particle image velocimetry （PIV） measurements. It is shown that the CFD simulations using the LES approach and the standard κ-ε model agree well with the PIV measurements. Fluctuations of the radial and axial velocity are predicted at different frequencies by the LES simulation. Velocity fluctuations of high frequencies are seen in the impeller region, while low frequencies velocity fluctuations are observed in the bulk flow. A low frequency velocity fluctuation with a nondimensional frequency of 0.027Hz is predicted by the LES simulation, which agrees with experimental investigations in the literature. Flow circulation patterns predicted by the LES simulation are asymmetric, stochastic and complex, spanning a large portion of the tanks and varying with time, while circulation patterns calculated by the simulation using the standard κ-ε model are symmetric. The results of the present work give better understanding to the flow instabilities in the mechanically agitated tank. However, further analysis of the LES calculated velocity series by means of fast Fourier transform （FFT） and/or spectra analysis are recommended in future work in order to gain more knowledge of the complicated flow phenomena.展开更多
Single-phase flow patterns generated by axial impeller are investigated by 3D Particle Dynamic Analyzer. Mean flow and turbulence intensities are measured for the impeller zone and the bulk regions. The effect of D/T ...Single-phase flow patterns generated by axial impeller are investigated by 3D Particle Dynamic Analyzer. Mean flow and turbulence intensities are measured for the impeller zone and the bulk regions. The effect of D/T and blade tip angle on flow pattern is studied as well. The measured results show that the flow in impeller zone oscillates periodically at the frequency of blade sweep. The flow patterns generated by different ratios of impeller diameter to tank diameter impeller are approximately the same below impellers,but a small second recirculation loop is formed in the upper part of vessel at the ratio of impeller diameter to tank diameter D/T=0.35.展开更多
The mean and r.m.s velocities of solid-liquid flow system were measured by Particle Dynamic Analyzer in a fully baffled tank agitated by axial impellers.The effect of particle volumetric concentration was investigated...The mean and r.m.s velocities of solid-liquid flow system were measured by Particle Dynamic Analyzer in a fully baffled tank agitated by axial impellers.The effect of particle volumetric concentration was investigated as well.The results showed that the velocity profiles for two-phase flow were similar with those of the single-phase flow in the impeller region.The axial velocities for two-phase flow were higher than corresponding velocities of single-phase,and the maximum relative velocity occurred at the blade tip with 0.03 U tip in value.The turbulence levels were in general lower,about 50% reduction,than those of single-phase flow in the impeller region.Tangential velocities of two-phase flow decreased with increasing particle concentration while the axial velocities remained the same.Due to the presence of the particles,the discharge jet width became narrow.展开更多
文摘The aim of this work is to investigate the flow instabilities in a baffled, stirred tank generated by a single Rushton turbine by means of large eddy simulation （LES）. The sliding mesh method was used for the coupling between the rotating and the stationary frame of references. The calculations were carried out on the ＂Shengcao-21C＂ supercomputer using a computational fluid dynamics （CFD） code CFX5. The flow fields predicted by the LES simulation and the simulation using standard κ-ε model were compared to the results from particle image velocimetry （PIV） measurements. It is shown that the CFD simulations using the LES approach and the standard κ-ε model agree well with the PIV measurements. Fluctuations of the radial and axial velocity are predicted at different frequencies by the LES simulation. Velocity fluctuations of high frequencies are seen in the impeller region, while low frequencies velocity fluctuations are observed in the bulk flow. A low frequency velocity fluctuation with a nondimensional frequency of 0.027Hz is predicted by the LES simulation, which agrees with experimental investigations in the literature. Flow circulation patterns predicted by the LES simulation are asymmetric, stochastic and complex, spanning a large portion of the tanks and varying with time, while circulation patterns calculated by the simulation using the standard κ-ε model are symmetric. The results of the present work give better understanding to the flow instabilities in the mechanically agitated tank. However, further analysis of the LES calculated velocity series by means of fast Fourier transform （FFT） and/or spectra analysis are recommended in future work in order to gain more knowledge of the complicated flow phenomena.
文摘Single-phase flow patterns generated by axial impeller are investigated by 3D Particle Dynamic Analyzer. Mean flow and turbulence intensities are measured for the impeller zone and the bulk regions. The effect of D/T and blade tip angle on flow pattern is studied as well. The measured results show that the flow in impeller zone oscillates periodically at the frequency of blade sweep. The flow patterns generated by different ratios of impeller diameter to tank diameter impeller are approximately the same below impellers,but a small second recirculation loop is formed in the upper part of vessel at the ratio of impeller diameter to tank diameter D/T=0.35.
文摘The mean and r.m.s velocities of solid-liquid flow system were measured by Particle Dynamic Analyzer in a fully baffled tank agitated by axial impellers.The effect of particle volumetric concentration was investigated as well.The results showed that the velocity profiles for two-phase flow were similar with those of the single-phase flow in the impeller region.The axial velocities for two-phase flow were higher than corresponding velocities of single-phase,and the maximum relative velocity occurred at the blade tip with 0.03 U tip in value.The turbulence levels were in general lower,about 50% reduction,than those of single-phase flow in the impeller region.Tangential velocities of two-phase flow decreased with increasing particle concentration while the axial velocities remained the same.Due to the presence of the particles,the discharge jet width became narrow.
