Reversible pump turbines are widely employed in the pumped hydro energy storage power plants. The frequent shifts among various operational modes for the reversible pump turbines pose various instability problems, e.g...Reversible pump turbines are widely employed in the pumped hydro energy storage power plants. The frequent shifts among various operational modes for the reversible pump turbines pose various instability problems, e.g., the strong pressure fluctuation, the shaft swing, and the impeller damage. The instability is related to the vortices generated in the channels of the reversible pump turbines in the generating mode. In the present paper, a new omega vortex identification method is applied to the vortex analysis of the reversible pump turbines. The main advantage of the adopted algorithm is that it is physically independent of the selected values for the vortex identification in different working modes. Both weak and strong vortices can be identified by setting the same omega value in the whole passage of the reversible pump turbine. Five typical modes（turbine mode, runaway mode, turbine brake mode, zero-flow-rate mode and reverse pump mode） at several typical guide vane openings are selected for the analysis and comparisons. The differences between various modes and different guide vane openings are compared both qualitatively in terms of the vortex distributions and quantitatively in terms of the areas of the vortices in the reversible pump turbines. Our findings indicate that the new omega method could be successfully applied to the vortex identification in the reversible pump turbines.展开更多
本文用Monte Carlo模拟实现Ω型分子筛中硅铝分布的物理模型,把由此计算获得的{Si_k(nAl)}结构单元相对数量与^(29)Si MAS NMR实验及Klinowski等的统计计算结果相比较,无论是B位{Si_B(nAl)},还是A位{Si_A(nAl)}分布,从总体上全面的逼近...本文用Monte Carlo模拟实现Ω型分子筛中硅铝分布的物理模型,把由此计算获得的{Si_k(nAl)}结构单元相对数量与^(29)Si MAS NMR实验及Klinowski等的统计计算结果相比较,无论是B位{Si_B(nAl)},还是A位{Si_A(nAl)}分布,从总体上全面的逼近NMR实验分析值.对铝浓度不很高时^(29)SiMAS NMR实验分析呈现出的Isi_(?)(2Al)>Isi_(?)(1Al)的令人费解的情况,也得到了初步阐明.这说明,本文提出的T_B位硅有同时桥联两个骨架铝原子的倾向假设是合理和自洽的,也是影响Ω型分子筛中硅、铝分布的一个因素.展开更多
The newly developed vortex-identification method,Liutex,has provided a new systematic description of the local fluid rotation,which includes scalar,vector,and tensor forms.However,the advantages of Liutex over the oth...The newly developed vortex-identification method,Liutex,has provided a new systematic description of the local fluid rotation,which includes scalar,vector,and tensor forms.However,the advantages of Liutex over the other widely used vortexidentification methods such as Q,Δ,λ2,andλci have not been realized.These traditional methods count on shearing and stretching as a part of vortex strength.But,in the real flow,shearing and stretching do not contribute to fluid rotation.In this paper,the decomposition of the velocity gradient tensor is conducted in the Principal Coordinate for uniqueness.Then the contamination effects of stretching and shearing of the traditional methods are investigated and compared with the Liutex method in terms of mathematical analysis and numerical calculations.The results show that the Liutex method is the only method that is not affected by either stretching or shear,as it represents only the local fluid rigid rotation.These results provide supporting evidence that Liutex is the superior method over others.展开更多
基金Project supported by the National Key R&D Program of China(Project No.2018YFB0604304-04)the National Natural Science Foundation of China(Grant No.51506051)
文摘Reversible pump turbines are widely employed in the pumped hydro energy storage power plants. The frequent shifts among various operational modes for the reversible pump turbines pose various instability problems, e.g., the strong pressure fluctuation, the shaft swing, and the impeller damage. The instability is related to the vortices generated in the channels of the reversible pump turbines in the generating mode. In the present paper, a new omega vortex identification method is applied to the vortex analysis of the reversible pump turbines. The main advantage of the adopted algorithm is that it is physically independent of the selected values for the vortex identification in different working modes. Both weak and strong vortices can be identified by setting the same omega value in the whole passage of the reversible pump turbine. Five typical modes（turbine mode, runaway mode, turbine brake mode, zero-flow-rate mode and reverse pump mode） at several typical guide vane openings are selected for the analysis and comparisons. The differences between various modes and different guide vane openings are compared both qualitatively in terms of the vortex distributions and quantitatively in terms of the areas of the vortices in the reversible pump turbines. Our findings indicate that the new omega method could be successfully applied to the vortex identification in the reversible pump turbines.
文摘本文用Monte Carlo模拟实现Ω型分子筛中硅铝分布的物理模型,把由此计算获得的{Si_k(nAl)}结构单元相对数量与^(29)Si MAS NMR实验及Klinowski等的统计计算结果相比较,无论是B位{Si_B(nAl)},还是A位{Si_A(nAl)}分布,从总体上全面的逼近NMR实验分析值.对铝浓度不很高时^(29)SiMAS NMR实验分析呈现出的Isi_(?)(2Al)>Isi_(?)(1Al)的令人费解的情况,也得到了初步阐明.这说明,本文提出的T_B位硅有同时桥联两个骨架铝原子的倾向假设是合理和自洽的,也是影响Ω型分子筛中硅、铝分布的一个因素.
文摘The newly developed vortex-identification method,Liutex,has provided a new systematic description of the local fluid rotation,which includes scalar,vector,and tensor forms.However,the advantages of Liutex over the other widely used vortexidentification methods such as Q,Δ,λ2,andλci have not been realized.These traditional methods count on shearing and stretching as a part of vortex strength.But,in the real flow,shearing and stretching do not contribute to fluid rotation.In this paper,the decomposition of the velocity gradient tensor is conducted in the Principal Coordinate for uniqueness.Then the contamination effects of stretching and shearing of the traditional methods are investigated and compared with the Liutex method in terms of mathematical analysis and numerical calculations.The results show that the Liutex method is the only method that is not affected by either stretching or shear,as it represents only the local fluid rigid rotation.These results provide supporting evidence that Liutex is the superior method over others.
