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
基于耦合模式比较计划第6阶段(the coupled model intercomparison program in phase 6,CMIP6)的全球气候模式模拟数据,评估分析了全球气候模式对中国主要地区1979―2014年极端气温与极端降水特征的模拟能力。通过泰勒图及各种统计参数...基于耦合模式比较计划第6阶段(the coupled model intercomparison program in phase 6,CMIP6)的全球气候模式模拟数据,评估分析了全球气候模式对中国主要地区1979―2014年极端气温与极端降水特征的模拟能力。通过泰勒图及各种统计参数的对比表明,全球气候模式对中国各个地区的极端降水/气温的模拟存在显著差异,对中国地区极端气温与降水模拟最好的模式是EC-Earth3。对EC-Earth3在4种未来情景下的气温/降水数据进行偏差校正,并对中国地区未来时期极端降水/气温进行了预估。结果表明:2021—2100年,中国地区升温趋势和极端降水的增加趋势显著,4种情景下的极端气温指标和极端降水指标在21世纪50年代之前是相似的,但之后变化趋势差异增加;SSP1-2.6情景下,2021—2100年升温速率和极端降水速率增加趋势较为平缓;SSP2-4.5、SSP3-7.0、SSP5-8.53种情景下,升温速率和极端降水增加速率随着模式和时间增加逐渐增大。展开更多
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.
文摘基于耦合模式比较计划第6阶段(the coupled model intercomparison program in phase 6,CMIP6)的全球气候模式模拟数据,评估分析了全球气候模式对中国主要地区1979―2014年极端气温与极端降水特征的模拟能力。通过泰勒图及各种统计参数的对比表明,全球气候模式对中国各个地区的极端降水/气温的模拟存在显著差异,对中国地区极端气温与降水模拟最好的模式是EC-Earth3。对EC-Earth3在4种未来情景下的气温/降水数据进行偏差校正,并对中国地区未来时期极端降水/气温进行了预估。结果表明:2021—2100年,中国地区升温趋势和极端降水的增加趋势显著,4种情景下的极端气温指标和极端降水指标在21世纪50年代之前是相似的,但之后变化趋势差异增加;SSP1-2.6情景下,2021—2100年升温速率和极端降水速率增加趋势较为平缓;SSP2-4.5、SSP3-7.0、SSP5-8.53种情景下,升温速率和极端降水增加速率随着模式和时间增加逐渐增大。
