The flow fields in a dual Rushton impeller stirred tank with diameter of 0.48 m (T) were measured by using Particle Image Velocimetry (PIV). Three different size impellers were used in the experiments with diamete...The flow fields in a dual Rushton impeller stirred tank with diameter of 0.48 m (T) were measured by using Particle Image Velocimetry (PIV). Three different size impellers were used in the experiments with diameters of D = 0.33T, 0.40T and 0.50T, respectively. The multi-block and 360° ensemble-averaged approaches were used to measure the radial and axial angle-resolved velocity distributions. Three typical flow patterns, named, merging flow, parallel flow and diverging flow, were obtained by changing the clearance of the bottom impeller above the tank base (C1) and the spacing between the two impellers (C2). The results show that while C1 is equal to D, the parallel flow occurs as C2≥0.40T, C2≥0.38T and C2≥0.32T and the merging flow occurs as C2≤0.38T, C2≤0.36T and C2≤0.27T for the impellers with diameter of D=0.33T, 0.40T and 0.50T, respectively. When C2 is equal to D, the diverging flow occurs in the value of C1≤0.15T for all three impellers. The flow numbers of these impellers were calculated for the parallel flow. Trailing vortices generated by the lower impeller for the diverging flow were shown by the 10° angle-resolved velocity measurements. The peak value of turbulence kinetic energy ( k/V^2tip = 0.12-0.15 or above) appears along the center of the impeller discharging stream.展开更多
Complex segregation occurs in a binary particle system with differing particle sizes and densities,particularly when the larger particles are heavier(S–D system,i.e.,size minus density system).Predicting the segregat...Complex segregation occurs in a binary particle system with differing particle sizes and densities,particularly when the larger particles are heavier(S–D system,i.e.,size minus density system).Predicting the segregation pattern driven by multiple mechanisms simultaneously is often challenging.This study explores the segregation mechanisms in a quasi-2D circular drum containing a S–D system,realizing a transition between the S-core and Core-and-band patterns by adjusting the drum rotation speed.During the transition of the segregation pattern,only the S-core pattern chiefly driven by the percolation mechanism is initially observed.As the rotation speed increases,the buoyancy mechanism and particle diffusion gradually strengthen,jointly driving the formation of the Core-and-band pattern.A dimensionless strength ratio,λ=H/h,where H and h respectively represent the diffusion and buoyancy strengths at length scales,is introduced to elucidate this transition.The Core-and-band pattern emerges whenλreached 1.4.展开更多
As an integral part of the internal air system of aero-engines,the axial throughflow of the cooling air can interact with the cavity flow between the rotating compressor disks,forming a threedimensional,unsteady,and u...As an integral part of the internal air system of aero-engines,the axial throughflow of the cooling air can interact with the cavity flow between the rotating compressor disks,forming a threedimensional,unsteady,and unstable flow field.The flow characteristics in an engine-like rotating multi-stage cavity with throughflow were investigated using particle image velocimetry,flow visualization technology and three-dimensional unsteady Reynolds-Averaged Navier-Stokes (RANS)simulations.The focus of current research was to understand the distribution of the mean swirl ratio and its variation with a wide range of non-dimensional parameters in the co-rotating cavity with high inlet pre-swirl axial throughflow.The maximum axial Reynolds number and rotational Reynolds numbers could reach 4.41×10^(4)and 1.24×10^(6),respectively.The velocity measurement results indicate that the mean swirl ratio is greater than 1 and decreases with an increase in the radial position.The flow structure is dominated by the Rossby number,and two different flow patterns (flow penetration and flow stratification) are identified and confirmed by flow visualization images.In the absence of buoyancy,the flow penetration caused by the precession of the throughflow makes it easier for the throughflow to reach a high radius region.Satisfactory consistency of results between measurements and numerical calculations is obtained.This study provides a theoretical basis and data support for toroidal vortex breakdown,which is of practical significance for the design of high-pressure compressor cavities.展开更多
To explore the effects of freeze‒thaw cycles on the mechanical properties and crack evolution of fissured sandstone,biaxial compression experiments were carried out on sandstone subjected to freeze‒thaw cycles to char...To explore the effects of freeze‒thaw cycles on the mechanical properties and crack evolution of fissured sandstone,biaxial compression experiments were carried out on sandstone subjected to freeze‒thaw cycles to characterize the changes in the physical and mechanical properties of fissured sandstone caused by freeze‒thaw cycles.The crack evolution and crack change process on the surface of the fissured sandstone were recorded and analysed in detail via digital image technology(DIC).Numerical simulation was used to reveal the expansion process and damage mode of fine-scale cracks under the action of freeze‒thaw cycles,and the simulation results were compared and analysed with the experimental data to verify the reliability of the numerical model.The results show that the mass loss,porosity,peak stress and elastic modulus all increase with increasing number of freeze‒thaw cycles.With an increase in the number of freeze‒thaw cycles,a substantial change in displacement occurs around the prefabricated cracks,and a stress concentration appears at the crack tip.As new cracks continue to sprout at the tips of the prefabricated cracks until the microcracks gradually penetrate into the main cracks,the displacement cloud becomes obviously discontinuous,and the contours of the displacement field in the crack fracture damage area simply intersect with the prefabricated cracks to form an obvious fracture.The damage patterns of the fractured sandstone after freeze‒thaw cycles clearly differ,forming a symmetrical"L"-shaped damage pattern at zero freeze‒thaw cycles,a symmetrical"V"-shaped damage pattern at 10 freeze‒thaw cycles,and a"V"-shaped damage pattern at 20 freeze‒thaw cycles.After 20 freeze‒thaw cycles,a"V"-shaped destruction pattern and"L"-shaped destruction pattern are formed;after 30 freeze‒thaw cycles,an"N"-shaped destruction pattern is formed.This shows that the failure mode of fractured sandstone gradually becomes more complicated with an increasing number of freeze‒thaw cycles.The effects展开更多
Organic matter is crucial in aerosol-climate interactions,yet the physicochemical properties and origins of organic aerosols remain poorly understood.Here we show the seasonal characteristics of submicron organic aero...Organic matter is crucial in aerosol-climate interactions,yet the physicochemical properties and origins of organic aerosols remain poorly understood.Here we show the seasonal characteristics of submicron organic aerosols in Arctic Svalbard during spring and summer,emphasizing their connection to transport patterns and particle size distribution.Microbial-derived organic matter(MOM)and terrestrial-derived organic matter(TOM)accounted for over 90%of the total organic mass in Arctic aerosols during these seasons,comprising carbohydrate/protein-like and lignin/tannin-like compounds,respectively.In spring,aerosols showed high TOM and low MOM intensities due to biomass-burning influx in the central Arctic.In contrast,summer exhibited elevated MOM intensity,attributed to the shift in predominant atmospheric transport from the central Arctic to the biologically active Greenland Sea.MOM and TOM were associated with Aitken mode particles(<100 nm diameter)and accumulation mode particles(>100 nm diameter),respectively.This association is linked to the molecular size of biomolecules,impacting the number concentrations of corresponding aerosol classes.These findings highlight the importance of considering seasonal atmospheric transport patterns and organic source-dependent particle size distributions in assessing aerosol properties in the changing Arctic.展开更多
基金Supported by the National Natural Science Foundation of China (20776008)and the National Basic Research Program of China (2007CB714300).
文摘The flow fields in a dual Rushton impeller stirred tank with diameter of 0.48 m (T) were measured by using Particle Image Velocimetry (PIV). Three different size impellers were used in the experiments with diameters of D = 0.33T, 0.40T and 0.50T, respectively. The multi-block and 360° ensemble-averaged approaches were used to measure the radial and axial angle-resolved velocity distributions. Three typical flow patterns, named, merging flow, parallel flow and diverging flow, were obtained by changing the clearance of the bottom impeller above the tank base (C1) and the spacing between the two impellers (C2). The results show that while C1 is equal to D, the parallel flow occurs as C2≥0.40T, C2≥0.38T and C2≥0.32T and the merging flow occurs as C2≤0.38T, C2≤0.36T and C2≤0.27T for the impellers with diameter of D=0.33T, 0.40T and 0.50T, respectively. When C2 is equal to D, the diverging flow occurs in the value of C1≤0.15T for all three impellers. The flow numbers of these impellers were calculated for the parallel flow. Trailing vortices generated by the lower impeller for the diverging flow were shown by the 10° angle-resolved velocity measurements. The peak value of turbulence kinetic energy ( k/V^2tip = 0.12-0.15 or above) appears along the center of the impeller discharging stream.
基金supported by Qingdao National Laboratory for Marine Science and Technology(grant No.2015ASKJ01)National Natural Science Foundation of China(grant Nos.12072200,12372384)Program of Shanghai Academic Research Leader(grant No.23XD1421400).
文摘Complex segregation occurs in a binary particle system with differing particle sizes and densities,particularly when the larger particles are heavier(S–D system,i.e.,size minus density system).Predicting the segregation pattern driven by multiple mechanisms simultaneously is often challenging.This study explores the segregation mechanisms in a quasi-2D circular drum containing a S–D system,realizing a transition between the S-core and Core-and-band patterns by adjusting the drum rotation speed.During the transition of the segregation pattern,only the S-core pattern chiefly driven by the percolation mechanism is initially observed.As the rotation speed increases,the buoyancy mechanism and particle diffusion gradually strengthen,jointly driving the formation of the Core-and-band pattern.A dimensionless strength ratio,λ=H/h,where H and h respectively represent the diffusion and buoyancy strengths at length scales,is introduced to elucidate this transition.The Core-and-band pattern emerges whenλreached 1.4.
文摘As an integral part of the internal air system of aero-engines,the axial throughflow of the cooling air can interact with the cavity flow between the rotating compressor disks,forming a threedimensional,unsteady,and unstable flow field.The flow characteristics in an engine-like rotating multi-stage cavity with throughflow were investigated using particle image velocimetry,flow visualization technology and three-dimensional unsteady Reynolds-Averaged Navier-Stokes (RANS)simulations.The focus of current research was to understand the distribution of the mean swirl ratio and its variation with a wide range of non-dimensional parameters in the co-rotating cavity with high inlet pre-swirl axial throughflow.The maximum axial Reynolds number and rotational Reynolds numbers could reach 4.41×10^(4)and 1.24×10^(6),respectively.The velocity measurement results indicate that the mean swirl ratio is greater than 1 and decreases with an increase in the radial position.The flow structure is dominated by the Rossby number,and two different flow patterns (flow penetration and flow stratification) are identified and confirmed by flow visualization images.In the absence of buoyancy,the flow penetration caused by the precession of the throughflow makes it easier for the throughflow to reach a high radius region.Satisfactory consistency of results between measurements and numerical calculations is obtained.This study provides a theoretical basis and data support for toroidal vortex breakdown,which is of practical significance for the design of high-pressure compressor cavities.
基金supported by the National Natural Science Foundation of China(Project No.52074123).
文摘To explore the effects of freeze‒thaw cycles on the mechanical properties and crack evolution of fissured sandstone,biaxial compression experiments were carried out on sandstone subjected to freeze‒thaw cycles to characterize the changes in the physical and mechanical properties of fissured sandstone caused by freeze‒thaw cycles.The crack evolution and crack change process on the surface of the fissured sandstone were recorded and analysed in detail via digital image technology(DIC).Numerical simulation was used to reveal the expansion process and damage mode of fine-scale cracks under the action of freeze‒thaw cycles,and the simulation results were compared and analysed with the experimental data to verify the reliability of the numerical model.The results show that the mass loss,porosity,peak stress and elastic modulus all increase with increasing number of freeze‒thaw cycles.With an increase in the number of freeze‒thaw cycles,a substantial change in displacement occurs around the prefabricated cracks,and a stress concentration appears at the crack tip.As new cracks continue to sprout at the tips of the prefabricated cracks until the microcracks gradually penetrate into the main cracks,the displacement cloud becomes obviously discontinuous,and the contours of the displacement field in the crack fracture damage area simply intersect with the prefabricated cracks to form an obvious fracture.The damage patterns of the fractured sandstone after freeze‒thaw cycles clearly differ,forming a symmetrical"L"-shaped damage pattern at zero freeze‒thaw cycles,a symmetrical"V"-shaped damage pattern at 10 freeze‒thaw cycles,and a"V"-shaped damage pattern at 20 freeze‒thaw cycles.After 20 freeze‒thaw cycles,a"V"-shaped destruction pattern and"L"-shaped destruction pattern are formed;after 30 freeze‒thaw cycles,an"N"-shaped destruction pattern is formed.This shows that the failure mode of fractured sandstone gradually becomes more complicated with an increasing number of freeze‒thaw cycles.The effects
基金National Research Foundation(NRF)of Korea NRF-2021M1A5A1065425(KOPRI-PN24011)The FT-ICR MS analysis was supported by the Korea Basic Science Institute under the R&D program(Project No.C330430)supervised by the Ministry of Science and ICT.
文摘Organic matter is crucial in aerosol-climate interactions,yet the physicochemical properties and origins of organic aerosols remain poorly understood.Here we show the seasonal characteristics of submicron organic aerosols in Arctic Svalbard during spring and summer,emphasizing their connection to transport patterns and particle size distribution.Microbial-derived organic matter(MOM)and terrestrial-derived organic matter(TOM)accounted for over 90%of the total organic mass in Arctic aerosols during these seasons,comprising carbohydrate/protein-like and lignin/tannin-like compounds,respectively.In spring,aerosols showed high TOM and low MOM intensities due to biomass-burning influx in the central Arctic.In contrast,summer exhibited elevated MOM intensity,attributed to the shift in predominant atmospheric transport from the central Arctic to the biologically active Greenland Sea.MOM and TOM were associated with Aitken mode particles(<100 nm diameter)and accumulation mode particles(>100 nm diameter),respectively.This association is linked to the molecular size of biomolecules,impacting the number concentrations of corresponding aerosol classes.These findings highlight the importance of considering seasonal atmospheric transport patterns and organic source-dependent particle size distributions in assessing aerosol properties in the changing Arctic.