In this paper,the CFD simulation and new flow unsteadiness analysis for a single-blade centrifugal pump with whole flow passage were carried out.The periodic flow unsteadiness has been quantitatively investigated in d...In this paper,the CFD simulation and new flow unsteadiness analysis for a single-blade centrifugal pump with whole flow passage were carried out.The periodic flow unsteadiness has been quantitatively investigated in detail by defining unsteady intensity and turbulence intensity in both rotor and volute domains under design condition Q=33 L s 1.The results show that the distributions of flow unsteadiness are the functions of impeller rotating angle and have complex unsteady characteristics.The obvious T u fluctuations can be also observed for different impeller positions.In addition,time-averaged unsteady intensity and time-averaged turbulence intensity were calculated by averaging the results of each mesh node for entire impeller revolution period to evaluate the strength distributions of flow unsteadiness directly and comprehensively.The accumulative results of an impeller revolution can directly show the positions and strength of the flow unsteadiness and turbulence intensity in both rotor and stator domains which can be an important aspect to be considered in the single-blade pump optimum design procedure for obtaining more stable inner flow of the pump and decreasing flow-induced vibration and noise.The flow unsteadiness in the side chamber cannot be neglected for an accurate prediction of the inner flow of the pump,and the optimizing design procedure for a single-blade pump impeller will not be accurate using CFD tool if the unsteady flow phenomenon in the side chamber is not considered.展开更多
Avalanches and landslides,induced by the Wenchuan Earthquake on May 12,2008,resulted in a lot of disaggregated,solid material on slopes that could be readily mobilized as source material for debris flows.Rainstorms tr...Avalanches and landslides,induced by the Wenchuan Earthquake on May 12,2008,resulted in a lot of disaggregated,solid material on slopes that could be readily mobilized as source material for debris flows.Rainstorms triggered numerous slope debris flows with great damage to highways and rivers over the subsequent two years.Slope debris flows(as opposed to channelized debris flows) are defined as phenomena in which high-concentration mixtures of debris and water flow down slopes for short distances to highways and river banks.Based on field investigations and measurements of 19 slope debris flows,their main characteristics and potential mitigation strategies were studied.High rainfall intensity is the main triggering factor.Critical rainfall intensities for simultaneous occurrence of single,several and numerous slope debris flow events were 20 mm/day,30mm/day,and 90 mm/day,respectively.Field investigations also revealed that slope debris flows consist of high concentrations of cobbles,boulders and gravel.They are two-phase debris flows.The liquid phase plays the role of lubrication instead of transporting medium.Solid particles collide with each other and consume a lot of energy.The velocities of slope debris flows are very low,and their transport distances are only several tens of meters.Slope debris flows may be controlled by construction of drainage systems and by reforestation.展开更多
To design a single-blade pump with a good performance in a wide operational range and to increase the pump reliability in the multi-conditional hydraulic design process, an understanding of the unsteady flow behaviors...To design a single-blade pump with a good performance in a wide operational range and to increase the pump reliability in the multi-conditional hydraulic design process, an understanding of the unsteady flow behaviors as related with the flow rate is very important. However, the traditional design often considers only a single design condition, and the unsteady flow behaviors have not been well studied for single-blade pumps under different conditions. A comparison analysis of the flow unsteadiness behaviors at di- fferent flow rates within the whole flow passage of the pump is carried out in this paper by solving the three-dimensional unsteady Reynolds-averaged Navier-Stokes equations with the Shear Stress Transport （SST） turbulence model. A definition of the unsteadiness in the pump is made and applied to analyze the unsteady intensity distributions, and the flow rate effect on the complex unsteady flow in the pump is studied quantitatively while the flow mechanism is also analyzed. The CFD results are validated by experimental data collected at the laboratory. It is shown that a significant flow rate effect on the time-averaged unsteadiness and the turbulence intensity distribution can be observed in both rotor and stator domains including the side chamber. The findings would be useful to reduce the flow unsteadiness and to increase the pump reliability under multi-conditions.展开更多
基金supported by the National Outstanding Young Scientists Founds of China (Grant No. 50825902)Jiangsu Provincial Project for Innovative Postgraduates of China (Grant No.CX10B_262Z)
文摘In this paper,the CFD simulation and new flow unsteadiness analysis for a single-blade centrifugal pump with whole flow passage were carried out.The periodic flow unsteadiness has been quantitatively investigated in detail by defining unsteady intensity and turbulence intensity in both rotor and volute domains under design condition Q=33 L s 1.The results show that the distributions of flow unsteadiness are the functions of impeller rotating angle and have complex unsteady characteristics.The obvious T u fluctuations can be also observed for different impeller positions.In addition,time-averaged unsteady intensity and time-averaged turbulence intensity were calculated by averaging the results of each mesh node for entire impeller revolution period to evaluate the strength distributions of flow unsteadiness directly and comprehensively.The accumulative results of an impeller revolution can directly show the positions and strength of the flow unsteadiness and turbulence intensity in both rotor and stator domains which can be an important aspect to be considered in the single-blade pump optimum design procedure for obtaining more stable inner flow of the pump and decreasing flow-induced vibration and noise.The flow unsteadiness in the side chamber cannot be neglected for an accurate prediction of the inner flow of the pump,and the optimizing design procedure for a single-blade pump impeller will not be accurate using CFD tool if the unsteady flow phenomenon in the side chamber is not considered.
基金supported by the Ministry of Science and Technology of China (2008CB425803)the State Key Laboratory of Hydroscience and Engineering at Tsinghua University (50823005,2009-ZY-2)
文摘Avalanches and landslides,induced by the Wenchuan Earthquake on May 12,2008,resulted in a lot of disaggregated,solid material on slopes that could be readily mobilized as source material for debris flows.Rainstorms triggered numerous slope debris flows with great damage to highways and rivers over the subsequent two years.Slope debris flows(as opposed to channelized debris flows) are defined as phenomena in which high-concentration mixtures of debris and water flow down slopes for short distances to highways and river banks.Based on field investigations and measurements of 19 slope debris flows,their main characteristics and potential mitigation strategies were studied.High rainfall intensity is the main triggering factor.Critical rainfall intensities for simultaneous occurrence of single,several and numerous slope debris flow events were 20 mm/day,30mm/day,and 90 mm/day,respectively.Field investigations also revealed that slope debris flows consist of high concentrations of cobbles,boulders and gravel.They are two-phase debris flows.The liquid phase plays the role of lubrication instead of transporting medium.Solid particles collide with each other and consume a lot of energy.The velocities of slope debris flows are very low,and their transport distances are only several tens of meters.Slope debris flows may be controlled by construction of drainage systems and by reforestation.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51239005,51009072)the National Science and Technology Pillar Program of China(GrantNo.2011BAF14B04)
文摘To design a single-blade pump with a good performance in a wide operational range and to increase the pump reliability in the multi-conditional hydraulic design process, an understanding of the unsteady flow behaviors as related with the flow rate is very important. However, the traditional design often considers only a single design condition, and the unsteady flow behaviors have not been well studied for single-blade pumps under different conditions. A comparison analysis of the flow unsteadiness behaviors at di- fferent flow rates within the whole flow passage of the pump is carried out in this paper by solving the three-dimensional unsteady Reynolds-averaged Navier-Stokes equations with the Shear Stress Transport （SST） turbulence model. A definition of the unsteadiness in the pump is made and applied to analyze the unsteady intensity distributions, and the flow rate effect on the complex unsteady flow in the pump is studied quantitatively while the flow mechanism is also analyzed. The CFD results are validated by experimental data collected at the laboratory. It is shown that a significant flow rate effect on the time-averaged unsteadiness and the turbulence intensity distribution can be observed in both rotor and stator domains including the side chamber. The findings would be useful to reduce the flow unsteadiness and to increase the pump reliability under multi-conditions.
