The three-dimensional unsteady turbulent flow in axial-flow pumps was simulated based on Navier-Stoke solver embedded with k - ε RNG turbulence model and SIMPLEC algorithm. Numerical results show that the unsteady pr...The three-dimensional unsteady turbulent flow in axial-flow pumps was simulated based on Navier-Stoke solver embedded with k - ε RNG turbulence model and SIMPLEC algorithm. Numerical results show that the unsteady prediction results are more accurate than the steady results, and the maximal error of unsteady prediction is only 4.54%. The time-domain spectrums show that the static pressure fluctuation curves at the inlet and outlet of the rotor and the outlet of the stator are periodic, and all have four peaks and four valleys. The pressure fluctuation amplitude increases from the hub to the tip at the inlet and outlet of the rotor, but decreases at the outlet of the stator. The pressure fluctuation amplitude is the greatest at the inlet of the rotor, and the average amplitude decreases sharply from the inlet to the outlet. The frequency spectrums obtained by Fast Fourier Transform （FFT） show that the dominant frequency is approximately equal to the blade passing frequency. The static pressure on the pressure side of hydrofoil on different stream surfaces remains almost consistent, and increases gradually from the blade inlet to the exit on the suction side at different time steps. The axial velocity distribution is periodic and is affected by the stator blade number at the rotor exit. The experimental results show that the flow is almost axial and the pre-rotation is very small at the rotor inlet under the conditions of 0.8 QN -1.2 QN Due to the clearance leakage, the pressure, circulation and meridional velocity at the rotor outlet all decrease near the hub leakage and tip clearance regions.展开更多
The interaction of flow through the inducer and impeller of an axial-flow pump equipped with an inducer has significant effect on its performance. This article presents a recent numerical investigation on this topic. ...The interaction of flow through the inducer and impeller of an axial-flow pump equipped with an inducer has significant effect on its performance. This article presents a recent numerical investigation on this topic. The studied pump has an inducer with 3 blades mounted on a conical hub and a 6-blade impeller. The blade angle of the impeller is adjustable to generate different relative circumferential angles between the inducer blade trailing edge and the impeller blade leading edge. A computational fluid dynamics code was used to investigate the flow characteristics and performance of the axial-flow pump. For turbulence closure, the RNG k-ε model was applied with an unstructured grid system. The rotor-stator interaction was treated with a Multiple Reference Frame （MRF） strategy. Computations were performed in different cases： 7 different relative circumferential angles （ Δθ ） between the inducer blade trailing edge and the impeller blade leading edge, and 3 different axial gaps （G） between the inducer and the impeller. The variation of the hydraulic loss in the rotator was obtained by changing Δθ . The numerical results show that the pressure generated is minimum in the case of （ G = 3%D）, which indicates that the interference between inducer and impeller is strong if the axial gap is small. The pump performances were predicted and compared to the experimental measurements. Recommendations for future modifications and improvements to the pump design were also given.展开更多
The flow with solid-liquid two-phase media inside centrifugal pumps is very complicated and the relevant method for the hydraulic design is still immature so far. There exist two main problems in the operation of the ...The flow with solid-liquid two-phase media inside centrifugal pumps is very complicated and the relevant method for the hydraulic design is still immature so far. There exist two main problems in the operation of the two-phase flow pumps, i.e., low overall efficiency and severe abrasion. In this study, the three-dimensional, steady, incompressible, and turbulent solid-liquid two-phase flows in a low-specific-speed centrifugal pump are numerically simulated and analyzed by using a computational fluid dynamics （CFD） code based on the mixture model of the two-phase flow and the RNG k-~ two-equation turbulence model, in which the influences of rotation and curvature are fully taken into account. The coupling between impeller and volute is implemented by means of the frozen rotor method. The simulation results predicted indicate that the solid phase properties in two-phase flow, especially the concentration, the particle diameter and the density, have strong effects on the hydraulic performance of the pump. Both the pump head and the efficiency are reduced with increasing particle diameter or concentration. However, the effect of particle density on the performance is relatively minor. An obvious jet-wake flow structure is presented near the volute tongue and becomes more remarkable with increasing solid phase concentration. The suction side of the blade is subject to much more severe abrasion than the pressure side. The obtained results preliminarily reveal the characteristics of solid-liquid two-phase flow in the centrifugal pump, and are helpful for improvement and empirical correction in the hydraulic design of centrifugal pumps.展开更多
This paper treats the flow instabilities in a mixed flow pump with a vaned diffuser. Test pump has a positive slope of a head-flow performance curve at 65% flow rate of BEP (Best Efficiency Point) because of a rotatin...This paper treats the flow instabilities in a mixed flow pump with a vaned diffuser. Test pump has a positive slope of a head-flow performance curve at 65% flow rate of BEP (Best Efficiency Point) because of a rotating stall. Dynamic Particle Image Velocimetry (PIV) and pressure fluctuation measurements are used for investigating the propagation mechanism of a rotating stall. It was found that unstable performance was caused by periodical large scale abrupt backflow generated from the vaned diffuser to the outlet of impeller. Further, the relation between the static pressure at the inlet of diffuser vane and the internal flow condition was clarified. From these experimental results, in order to improve the positive slope of a head-flow performance curve, to suppress the growth of strong vortex toward the inlet of diffuser vane was proved to be a key point.展开更多
The experimental investigation of axial-flow pump has been rapidly developed to meet the needs of South-to-North Water Diversion Project of China. Owing to the boundary conditions of hub, blade tip clearance, much of ...The experimental investigation of axial-flow pump has been rapidly developed to meet the needs of South-to-North Water Diversion Project of China. Owing to the boundary conditions of hub, blade tip clearance, much of the physical phenomena and laws involved in this complex flow field can＇t be fully determined. The flow characteristics of the high efficiency axial-flow pump have been simulated by RNG k-e turbulence model and SIMPLEC arithmetic based on FLUENT software. Numerical results indicate that the data from the prediction show agreement with the experimental results, static pressure on pressure side of blades increases slightly at circumferential direction with radius increasing, and keep almost constant at the same radial while increasing gradually from inlet to exit on the suction side along flow direction at design conditions. The static pressure, total pressure and velocity at inlet, impeller outlet and vane outlet were measured by a five-hole probe, and a contrastive experiment was done to investigate the influence of hub leakage. The experimental results show that inlet flow is almost axial and the prerotation is very small at various conditions. The meridional velocity and circulation distribution are almost identical at impeller outlet at design conditions due to steady flow and high efficiency. The residual circulation exits at downstream of the guide vane, and the circumferential velocity component increases linearly from hub to tip at small flow rate conditions. Hub leakage in adjustable blades results in the decrease of the meridional velocity and circulation at blade exit near hub. The results of numerical simulation and experiments supply important flow structure information for the high-efficiency axial-flow pump.展开更多
The pressure fluctuation in the flow passage of both impeller and casing is addressed on design condition. The initial conditions for the unsteady turbulent simulation are resulted from the steady calculations, and th...The pressure fluctuation in the flow passage of both impeller and casing is addressed on design condition. The initial conditions for the unsteady turbulent simulation are resulted from the steady calculations, and the three dimensional unsteady turbulent simulation concerning the rotor-stator interaction is executed by a Navier-Stoke solver embedded with k -ε turbulence model and with appropriate moving interface boundary conditions. Detecting points are distributed in the flow passage in different radial and circumferential positions to capture the static pressure fluctuation character for one cycle of the impeller. The time-domain spectrums show that the static pressure curves are periodic and have five peaks and five valleys. With the radius increasing, the pressure fluctuation peak-to-peak values in the impeller are increasing, and reach the maximum value on the interface. In the casing flow passage, those values are about 7% of local static pressure except some ones near the tongue. The values become decreasingly in the diffuser pipe. The frequency spectrums transformed by fast Fourier transform （FFT） show that the dominant frequency is approximate with the blade passing frequency, and the pressure fluctuations in impeller passage have high frequency content while those in casing ones have no such information.展开更多
One of the most important questions in the science of global change is how to balance the atmospheric CO2 budget. There is a large terrestrial missing carbon sink amounting to about one billion tonnes of carbon per an...One of the most important questions in the science of global change is how to balance the atmospheric CO2 budget. There is a large terrestrial missing carbon sink amounting to about one billion tonnes of carbon per annum. The locations, magnitudes, variations, and mechanisms responsible for this terrestrial missing carbon sink are uncertain and the focus of much continuing debate. Although the positive feedback between global change and silicate chemical weathering is used in geochemical models of atmospheric CO2, this feedback is believed to operate over a long timescale and is therefore generally left out of the current discussion of human impact upon the carbon budget. Here, we show, by synthesizing recent findings in rock weathering research and studies into biological carbon pump effects in surface aquatic ecosystems, that the carbon sink produced by carbonate weathering based on the H2O- carbonate-CO2-aquatic phototroph interaction on land not only totals half a billion tonnes per annum, but also displays a significant increasing trend under the influence of global warming and land use change; thus, it needs to be included in the global carbon budget.展开更多
High-efficiency design of a mixed-flow pump has been carried out based on numerical analysis of a three-dimensional viscous flow.For analysis,the Reynolds-averaged Navier-Stokes equations with a shear stress transport...High-efficiency design of a mixed-flow pump has been carried out based on numerical analysis of a three-dimensional viscous flow.For analysis,the Reynolds-averaged Navier-Stokes equations with a shear stress transport turbulence model were discretized by finite-volume approximations.Structured grid system was constructed in the computational domain,which has O-type grids near the blade surfaces and H/J-type grids in other regions.The numerical results were validated with experimental data for the heads and hydraulic efficiencies at different flow coefficients.The hydraulic efficiency at the design flow coefficient was evaluated with variation of the geometric variables,i.e.,the area of the discharge and length of the vane in the diffuser.The result has shown that the hydraulic efficiency of a mixed-flow pump at the design condition is improved by the modification of the geometry.展开更多
Echocardiography is the most common diagnostic method for assessing atrial function but the technique has some limitations. Traditionally, assessment of left atrial function has been performed by measuring volumes wit...Echocardiography is the most common diagnostic method for assessing atrial function but the technique has some limitations. Traditionally, assessment of left atrial function has been performed by measuring volumes with 2D echocardiography. Additionally, it can be assessed with transmitral Doppler and pulmonary vein Doppler. Recently, an alternative method has been incorporated, namely, measurement of myocardial deformation with color tissue Doppler-derived strain. However, this method has several limitations, such as suboptimal reproducibility, angle-dependence, signal artifacts and the fact that it only measures regional strain and does not obtain information about the curved portion of the atrial roof. To overcome these limitations in the quantification of atrial function, the use of speckle tracking echocardiography (STE) strain has been proposed. This technique is not derived from Doppler but rather from 2D echocardiography; it is angle-independent and allows one to measure global as well as regional atrial strain. In this editorial, we describe the physical and pathophysiological concepts of STE and underline the clinical usefulness of this new technique.展开更多
Numerical simulations of 3D turbulent flow in a large-bore axial-flow pump coupled with half-elbow suction sump were perlbrmed by using CFD approach. The numerical model and velocity and pressure distributions in enti...Numerical simulations of 3D turbulent flow in a large-bore axial-flow pump coupled with half-elbow suction sump were perlbrmed by using CFD approach. The numerical model and velocity and pressure distributions in entire flow passage were presented. The obvious backflow in half-elbow suction sump and strong flow nonuniformity at suction sump outlet were observed, whereas these phenomena were not observed in existing studies performed for a separate suction sump by either experimental or numerical approach. This result indicates that the interaction between half-elbow suction sump and impeller has significant effect on the flow distribution in the pump passage. The change of pump efficiency caused by the interaction was discussed,展开更多
基金Project supported by the National High Technology Research and Development Program of China (863 Program,Grant No.2007AA05Z207)the Graduate Student Innovation Foundation of Jiangsu Province (Grant No.CX08B_064Z)the National Science and Technology Support Program (Grant No.2008BAF34B15)
文摘The three-dimensional unsteady turbulent flow in axial-flow pumps was simulated based on Navier-Stoke solver embedded with k - ε RNG turbulence model and SIMPLEC algorithm. Numerical results show that the unsteady prediction results are more accurate than the steady results, and the maximal error of unsteady prediction is only 4.54%. The time-domain spectrums show that the static pressure fluctuation curves at the inlet and outlet of the rotor and the outlet of the stator are periodic, and all have four peaks and four valleys. The pressure fluctuation amplitude increases from the hub to the tip at the inlet and outlet of the rotor, but decreases at the outlet of the stator. The pressure fluctuation amplitude is the greatest at the inlet of the rotor, and the average amplitude decreases sharply from the inlet to the outlet. The frequency spectrums obtained by Fast Fourier Transform （FFT） show that the dominant frequency is approximately equal to the blade passing frequency. The static pressure on the pressure side of hydrofoil on different stream surfaces remains almost consistent, and increases gradually from the blade inlet to the exit on the suction side at different time steps. The axial velocity distribution is periodic and is affected by the stator blade number at the rotor exit. The experimental results show that the flow is almost axial and the pre-rotation is very small at the rotor inlet under the conditions of 0.8 QN -1.2 QN Due to the clearance leakage, the pressure, circulation and meridional velocity at the rotor outlet all decrease near the hub leakage and tip clearance regions.
基金the National Nature Science Foundation of China (Grant No. 90510007) Beijing Nature Science Foundation of China (Grant No. 3071002)the National Key Technology R and D Program (Grant No. 2006BAD11B07).
文摘The interaction of flow through the inducer and impeller of an axial-flow pump equipped with an inducer has significant effect on its performance. This article presents a recent numerical investigation on this topic. The studied pump has an inducer with 3 blades mounted on a conical hub and a 6-blade impeller. The blade angle of the impeller is adjustable to generate different relative circumferential angles between the inducer blade trailing edge and the impeller blade leading edge. A computational fluid dynamics code was used to investigate the flow characteristics and performance of the axial-flow pump. For turbulence closure, the RNG k-ε model was applied with an unstructured grid system. The rotor-stator interaction was treated with a Multiple Reference Frame （MRF） strategy. Computations were performed in different cases： 7 different relative circumferential angles （ Δθ ） between the inducer blade trailing edge and the impeller blade leading edge, and 3 different axial gaps （G） between the inducer and the impeller. The variation of the hydraulic loss in the rotator was obtained by changing Δθ . The numerical results show that the pressure generated is minimum in the case of （ G = 3%D）, which indicates that the interference between inducer and impeller is strong if the axial gap is small. The pump performances were predicted and compared to the experimental measurements. Recommendations for future modifications and improvements to the pump design were also given.
基金supported by National Natural Science Foundation of China (Grant No. 21076198)Zhejiang Provincial Natural Science Foundation of China (Granted No. R1100530)National Basic Research Program of China (973 Program,Grant No. 2009CB724303)
文摘The flow with solid-liquid two-phase media inside centrifugal pumps is very complicated and the relevant method for the hydraulic design is still immature so far. There exist two main problems in the operation of the two-phase flow pumps, i.e., low overall efficiency and severe abrasion. In this study, the three-dimensional, steady, incompressible, and turbulent solid-liquid two-phase flows in a low-specific-speed centrifugal pump are numerically simulated and analyzed by using a computational fluid dynamics （CFD） code based on the mixture model of the two-phase flow and the RNG k-~ two-equation turbulence model, in which the influences of rotation and curvature are fully taken into account. The coupling between impeller and volute is implemented by means of the frozen rotor method. The simulation results predicted indicate that the solid phase properties in two-phase flow, especially the concentration, the particle diameter and the density, have strong effects on the hydraulic performance of the pump. Both the pump head and the efficiency are reduced with increasing particle diameter or concentration. However, the effect of particle density on the performance is relatively minor. An obvious jet-wake flow structure is presented near the volute tongue and becomes more remarkable with increasing solid phase concentration. The suction side of the blade is subject to much more severe abrasion than the pressure side. The obtained results preliminarily reveal the characteristics of solid-liquid two-phase flow in the centrifugal pump, and are helpful for improvement and empirical correction in the hydraulic design of centrifugal pumps.
文摘This paper treats the flow instabilities in a mixed flow pump with a vaned diffuser. Test pump has a positive slope of a head-flow performance curve at 65% flow rate of BEP (Best Efficiency Point) because of a rotating stall. Dynamic Particle Image Velocimetry (PIV) and pressure fluctuation measurements are used for investigating the propagation mechanism of a rotating stall. It was found that unstable performance was caused by periodical large scale abrupt backflow generated from the vaned diffuser to the outlet of impeller. Further, the relation between the static pressure at the inlet of diffuser vane and the internal flow condition was clarified. From these experimental results, in order to improve the positive slope of a head-flow performance curve, to suppress the growth of strong vortex toward the inlet of diffuser vane was proved to be a key point.
基金supported by National Hi-tech Research and Development Program of China (863 Program, Grant No. 2007AA05Z207)National Science and Technology Support Scheme of China (Grant No. 2008BAF34B10)Jiangsu Provincial Graduate Student Innovation Foundation of China (Grant No. CX08B_064Z)
文摘The experimental investigation of axial-flow pump has been rapidly developed to meet the needs of South-to-North Water Diversion Project of China. Owing to the boundary conditions of hub, blade tip clearance, much of the physical phenomena and laws involved in this complex flow field can＇t be fully determined. The flow characteristics of the high efficiency axial-flow pump have been simulated by RNG k-e turbulence model and SIMPLEC arithmetic based on FLUENT software. Numerical results indicate that the data from the prediction show agreement with the experimental results, static pressure on pressure side of blades increases slightly at circumferential direction with radius increasing, and keep almost constant at the same radial while increasing gradually from inlet to exit on the suction side along flow direction at design conditions. The static pressure, total pressure and velocity at inlet, impeller outlet and vane outlet were measured by a five-hole probe, and a contrastive experiment was done to investigate the influence of hub leakage. The experimental results show that inlet flow is almost axial and the prerotation is very small at various conditions. The meridional velocity and circulation distribution are almost identical at impeller outlet at design conditions due to steady flow and high efficiency. The residual circulation exits at downstream of the guide vane, and the circumferential velocity component increases linearly from hub to tip at small flow rate conditions. Hub leakage in adjustable blades results in the decrease of the meridional velocity and circulation at blade exit near hub. The results of numerical simulation and experiments supply important flow structure information for the high-efficiency axial-flow pump.
基金supported by National Outstanding Young Scientists Funds of China (Grand No.50825902)
文摘The pressure fluctuation in the flow passage of both impeller and casing is addressed on design condition. The initial conditions for the unsteady turbulent simulation are resulted from the steady calculations, and the three dimensional unsteady turbulent simulation concerning the rotor-stator interaction is executed by a Navier-Stoke solver embedded with k -ε turbulence model and with appropriate moving interface boundary conditions. Detecting points are distributed in the flow passage in different radial and circumferential positions to capture the static pressure fluctuation character for one cycle of the impeller. The time-domain spectrums show that the static pressure curves are periodic and have five peaks and five valleys. With the radius increasing, the pressure fluctuation peak-to-peak values in the impeller are increasing, and reach the maximum value on the interface. In the casing flow passage, those values are about 7% of local static pressure except some ones near the tongue. The values become decreasingly in the diffuser pipe. The frequency spectrums transformed by fast Fourier transform （FFT） show that the dominant frequency is approximate with the blade passing frequency, and the pressure fluctuations in impeller passage have high frequency content while those in casing ones have no such information.
基金supported by the National BasicResearch Program of China(2013CB956703)the National Natural Science Foundation of China(41430753 and 41172232)
文摘One of the most important questions in the science of global change is how to balance the atmospheric CO2 budget. There is a large terrestrial missing carbon sink amounting to about one billion tonnes of carbon per annum. The locations, magnitudes, variations, and mechanisms responsible for this terrestrial missing carbon sink are uncertain and the focus of much continuing debate. Although the positive feedback between global change and silicate chemical weathering is used in geochemical models of atmospheric CO2, this feedback is believed to operate over a long timescale and is therefore generally left out of the current discussion of human impact upon the carbon budget. Here, we show, by synthesizing recent findings in rock weathering research and studies into biological carbon pump effects in surface aquatic ecosystems, that the carbon sink produced by carbonate weathering based on the H2O- carbonate-CO2-aquatic phototroph interaction on land not only totals half a billion tonnes per annum, but also displays a significant increasing trend under the influence of global warming and land use change; thus, it needs to be included in the global carbon budget.
基金supported by the Korea Institute of Industrial Technology Evaluation and Planning (ITEP) grant funded by the Ministry of Knowledge Economy (Grant No.10031771)
文摘High-efficiency design of a mixed-flow pump has been carried out based on numerical analysis of a three-dimensional viscous flow.For analysis,the Reynolds-averaged Navier-Stokes equations with a shear stress transport turbulence model were discretized by finite-volume approximations.Structured grid system was constructed in the computational domain,which has O-type grids near the blade surfaces and H/J-type grids in other regions.The numerical results were validated with experimental data for the heads and hydraulic efficiencies at different flow coefficients.The hydraulic efficiency at the design flow coefficient was evaluated with variation of the geometric variables,i.e.,the area of the discharge and length of the vane in the diffuser.The result has shown that the hydraulic efficiency of a mixed-flow pump at the design condition is improved by the modification of the geometry.
文摘Echocardiography is the most common diagnostic method for assessing atrial function but the technique has some limitations. Traditionally, assessment of left atrial function has been performed by measuring volumes with 2D echocardiography. Additionally, it can be assessed with transmitral Doppler and pulmonary vein Doppler. Recently, an alternative method has been incorporated, namely, measurement of myocardial deformation with color tissue Doppler-derived strain. However, this method has several limitations, such as suboptimal reproducibility, angle-dependence, signal artifacts and the fact that it only measures regional strain and does not obtain information about the curved portion of the atrial roof. To overcome these limitations in the quantification of atrial function, the use of speckle tracking echocardiography (STE) strain has been proposed. This technique is not derived from Doppler but rather from 2D echocardiography; it is angle-independent and allows one to measure global as well as regional atrial strain. In this editorial, we describe the physical and pathophysiological concepts of STE and underline the clinical usefulness of this new technique.
基金Project supported by the National Nature Science Foundation of China (Grant Nos: 10372114, 50479008 and 90510007) and Program for New Century Excellent Talents in Universities of China (Grant No: NCET-04-0133).
文摘Numerical simulations of 3D turbulent flow in a large-bore axial-flow pump coupled with half-elbow suction sump were perlbrmed by using CFD approach. The numerical model and velocity and pressure distributions in entire flow passage were presented. The obvious backflow in half-elbow suction sump and strong flow nonuniformity at suction sump outlet were observed, whereas these phenomena were not observed in existing studies performed for a separate suction sump by either experimental or numerical approach. This result indicates that the interaction between half-elbow suction sump and impeller has significant effect on the flow distribution in the pump passage. The change of pump efficiency caused by the interaction was discussed,
