Compared with front engine vehicle, the windward side’s flow field in cooling model of rear engine bus is complicated and it can’t be calculated by means of 1D model. For this problem, this paper has used Star-CCM t...Compared with front engine vehicle, the windward side’s flow field in cooling model of rear engine bus is complicated and it can’t be calculated by means of 1D model. For this problem, this paper has used Star-CCM to build a 3D simulation model of cooling system, engine compartment and complete vehicle. Then, it had a 1D/3D coupling calculation on cooling system with Kuli software. It could be helpful in the optimization design of the flow field of rear engine compartment and optimization match of cooling system.展开更多
By means of both a theory for pressure-induced shifts (PS) of energy spectra and a theory for shifts ofenergy spectra due to electron-phonon interaction (EPI), the 'pure electronic' PS and the PS due to EPI of...By means of both a theory for pressure-induced shifts (PS) of energy spectra and a theory for shifts ofenergy spectra due to electron-phonon interaction (EPI), the 'pure electronic' PS and the PS due to EPI of R1 line ofGSGG:Cr3+ at 70 K have been calculated, respectively. Their physical origins have been revealed. It is found that theremarkable under the normal pressure, and the degree of the admixture rapidly decreases with increasing pressure. Thechange of the degree of the admixture with the pressure plays a key role for not only the pure electronic PS of R1 line butalso the PS ofR1 line due to EPL The detailed calculations and analyses show that the pressure-dependent behaviors ofthe pure electronic PS of R1 line and the PS of R1 line due to EPI are quite different. It is the combined effect of themthat gives rise to the total PS of R1 line, which has satisfactorily explained the experimental data (including a reversal ofPS of R1 line). In contributions to PS of R1 line due to EPI at 70 K, the temperature-independent contribution is muchlarger than the temperature-dependent contribution. The former results from the interaction between the zero-pointvibration of the lattice and localized electronic state.展开更多
Although the hydraulic transients in pipe systems are usually simulated by using a one-dimensional (l-D) approach, local three-dimensional (3-D) simulations are necessary because of obvious 3-D flow features in so...Although the hydraulic transients in pipe systems are usually simulated by using a one-dimensional (l-D) approach, local three-dimensional (3-D) simulations are necessary because of obvious 3-D flow features in some local regions of the hydropower systems. This paper combines the 1-D method with a 3-D fluid flow model to simulate the Multi-Dimensional (MD) hydraulic transients in hydropower systems and proposes two methods for modeling the compressible water with the correct wave speed, and two strategies for efficiently coupling the 1-D and 3-D computational domains. The methods are validated by simulating the water hammer waves and the oscillations of the water level in a surge tank, and comparing the results ~with the 1-D solution data. An MD study is conducted for the transient flows in a realistic water conveying system that consists of a draft tube, a tailrace surge tank and a tailrace tunnel. It is shown that the 1-D-3-D coupling approach is an efficient and promising way to simulate the hydraulic transients in the hydropower systems in which the interactions between 1-D hydraulic fluctuations of the pipeline systems and the local 3-D flow patterns should be considered.展开更多
The vent tube is commonly used for the water hammer protection in the hydropower tailrace system. In transient processes, with air entering and exiting the vent tube, one sees complex hydraulic phenomena, which threat...The vent tube is commonly used for the water hammer protection in the hydropower tailrace system. In transient processes, with air entering and exiting the vent tube, one sees complex hydraulic phenomena, which threaten the station's safe operation. It is necessary to investigate the transient mechanisms in the tailrace system with vent tube. In this paper, a 3-D, two-phase numerical model of a vent tube on the connection of the tailrace tunnel and the diversion tunnel, is developed based on the FLUENT with the volume of fluid(VOF) algorithm to investigate the transient air-water flow patterns and the complex hydraulic phenomena in the vent tube of the tailrace system. A 1-D and 3-D unidirectional adjacent coupling(1-D-3-D-UAC) approach with a linear interpolation method is adopted to adjust the timesteps between the 1-D model and the 3-D model on the tunnel inlet and outlet boundaries through the user defined function(UDF), to transmit the data from the 1-D model to the 3-D model. The model is verified by comparing the results obtained by using the 1-D model alone and from the experiments in literature. The transient flow processes under the full load rejection consist of four stages: the water level dropping stage, the air entering stage, the air pocket collapsing stage, and the air exiting stage. Detailed hydraulic phenomena in the air pocket collapsing process are also discussed.展开更多
A theory for shifts of energy spectra due to electron-phonon interaction (EPI) has been developed. Both thetemperature-independent contributions and the temperature-dependent ones of acoustic branches and optical bran...A theory for shifts of energy spectra due to electron-phonon interaction (EPI) has been developed. Both thetemperature-independent contributions and the temperature-dependent ones of acoustic branches and optical brancheshave been derived. It is found that the temperature-independent contributions are very important, especially at lowtemperature. The total pressure-induced shift (PS) of a level (or spectral line or band) is the algebraic sum of its PSwithout EPI and its PS due to EPI. By means of both the theory for shifts of energy spectra due to EPI and the theoryfor PS of energy spectra, the total PS of R1 line of tunable laser crystal GSGG:Cr3+ at 70 K as well as the ones of itsR1 line, R2 line and U band at 300 K will be successfully calculated and explained in this series of papers.展开更多
Large-head variable-amplitude pump turbines(PTs) encounter serious transient hydraulic instability issues. To explore the evolution mechanisms of pressure fluctuations(PFs) and flow patterns inside large-head variable...Large-head variable-amplitude pump turbines(PTs) encounter serious transient hydraulic instability issues. To explore the evolution mechanisms of pressure fluctuations(PFs) and flow patterns inside large-head variable-amplitude PTs, the load rejection process(LRP) was investigated using a one-and three-dimensional coupled flow simulation approach. The temporal,spatial, and frequency characteristics of the fluctuating pressures were analyzed for four monitoring points using a combined time-frequency analysis approach. The results indicated that PFs during the LRP of large-head variable-amplitude PTs had a new fluctuation frequency component related to Dean vortices(DVs) in the volute, in addition to the common fluctuation frequency components related to rotor-stator interaction phenomena and local backflow vortices near the impeller inlet. The PF frequency component existed throughout the LRP and had a significant influence on the transient maximum pressure at the volute end. This study provides a useful theoretical guide for the design and optimization of large-head variable-amplitude PTs.展开更多
The Secondary Air System(SAS)plays an important role in the safe operation and performance of aeroengines.The traditional 1D-3D coupling method loses information when used for secondary air systems,which affects the c...The Secondary Air System(SAS)plays an important role in the safe operation and performance of aeroengines.The traditional 1D-3D coupling method loses information when used for secondary air systems,which affects the calculation accuracy.In this paper,a Cross-dimensional Data Transmission method(CDT)from 3D to 1D is proposed by introducing flow field uniformity into the data transmission.First,a uniformity index was established to quantify the flow field parameter distribution characteristics,and a uniformity index prediction model based on the locally weighted regression method(Lowess)was established to quickly obtain the flow field information.Then,an information selection criterion in 3D to 1D data transmission was established based on the Spearman rank correlation coefficient between the uniformity index and the accuracy of coupling calculation,and the calculation method was automatically determined according to the established criterion.Finally,a modified function was obtained by fitting the ratio of the 3D mass-average parameters to the analytical solution,which are then used to modify the selected parameters at the 1D-3D interface.Taking a typical disk cavity air system as an example,the results show that the calculation accuracy of the CDT method is greatly improved by a relative 53.88%compared with the traditional 1D-3D coupling method.Furthermore,the CDT method achieves a speedup of 2 to 3 orders of magnitude compared to the 3D calculation.展开更多
文摘Compared with front engine vehicle, the windward side’s flow field in cooling model of rear engine bus is complicated and it can’t be calculated by means of 1D model. For this problem, this paper has used Star-CCM to build a 3D simulation model of cooling system, engine compartment and complete vehicle. Then, it had a 1D/3D coupling calculation on cooling system with Kuli software. It could be helpful in the optimization design of the flow field of rear engine compartment and optimization match of cooling system.
文摘By means of both a theory for pressure-induced shifts (PS) of energy spectra and a theory for shifts ofenergy spectra due to electron-phonon interaction (EPI), the 'pure electronic' PS and the PS due to EPI of R1 line ofGSGG:Cr3+ at 70 K have been calculated, respectively. Their physical origins have been revealed. It is found that theremarkable under the normal pressure, and the degree of the admixture rapidly decreases with increasing pressure. Thechange of the degree of the admixture with the pressure plays a key role for not only the pure electronic PS of R1 line butalso the PS ofR1 line due to EPL The detailed calculations and analyses show that the pressure-dependent behaviors ofthe pure electronic PS of R1 line and the PS of R1 line due to EPI are quite different. It is the combined effect of themthat gives rise to the total PS of R1 line, which has satisfactorily explained the experimental data (including a reversal ofPS of R1 line). In contributions to PS of R1 line due to EPI at 70 K, the temperature-independent contribution is muchlarger than the temperature-dependent contribution. The former results from the interaction between the zero-pointvibration of the lattice and localized electronic state.
基金the National Natural Science Foundation of China (Grant Nos. 51039005, 50909076)
文摘Although the hydraulic transients in pipe systems are usually simulated by using a one-dimensional (l-D) approach, local three-dimensional (3-D) simulations are necessary because of obvious 3-D flow features in some local regions of the hydropower systems. This paper combines the 1-D method with a 3-D fluid flow model to simulate the Multi-Dimensional (MD) hydraulic transients in hydropower systems and proposes two methods for modeling the compressible water with the correct wave speed, and two strategies for efficiently coupling the 1-D and 3-D computational domains. The methods are validated by simulating the water hammer waves and the oscillations of the water level in a surge tank, and comparing the results ~with the 1-D solution data. An MD study is conducted for the transient flows in a realistic water conveying system that consists of a draft tube, a tailrace surge tank and a tailrace tunnel. It is shown that the 1-D-3-D coupling approach is an efficient and promising way to simulate the hydraulic transients in the hydropower systems in which the interactions between 1-D hydraulic fluctuations of the pipeline systems and the local 3-D flow patterns should be considered.
基金Project supported by the National Key R&D Program of China(Grant No.2016YFC0401810)the Research Project of Science and Technology Commission of Shanghai Munici-pality(Grant No.16DZ1202205)and the Fundamental Research Funds for the Central Universities(Grant No.2016B10814)
文摘The vent tube is commonly used for the water hammer protection in the hydropower tailrace system. In transient processes, with air entering and exiting the vent tube, one sees complex hydraulic phenomena, which threaten the station's safe operation. It is necessary to investigate the transient mechanisms in the tailrace system with vent tube. In this paper, a 3-D, two-phase numerical model of a vent tube on the connection of the tailrace tunnel and the diversion tunnel, is developed based on the FLUENT with the volume of fluid(VOF) algorithm to investigate the transient air-water flow patterns and the complex hydraulic phenomena in the vent tube of the tailrace system. A 1-D and 3-D unidirectional adjacent coupling(1-D-3-D-UAC) approach with a linear interpolation method is adopted to adjust the timesteps between the 1-D model and the 3-D model on the tunnel inlet and outlet boundaries through the user defined function(UDF), to transmit the data from the 1-D model to the 3-D model. The model is verified by comparing the results obtained by using the 1-D model alone and from the experiments in literature. The transient flow processes under the full load rejection consist of four stages: the water level dropping stage, the air entering stage, the air pocket collapsing stage, and the air exiting stage. Detailed hydraulic phenomena in the air pocket collapsing process are also discussed.
文摘A theory for shifts of energy spectra due to electron-phonon interaction (EPI) has been developed. Both thetemperature-independent contributions and the temperature-dependent ones of acoustic branches and optical brancheshave been derived. It is found that the temperature-independent contributions are very important, especially at lowtemperature. The total pressure-induced shift (PS) of a level (or spectral line or band) is the algebraic sum of its PSwithout EPI and its PS due to EPI. By means of both the theory for shifts of energy spectra due to EPI and the theoryfor PS of energy spectra, the total PS of R1 line of tunable laser crystal GSGG:Cr3+ at 70 K as well as the ones of itsR1 line, R2 line and U band at 300 K will be successfully calculated and explained in this series of papers.
基金supported by the National Natural Science Foundation of China(Grant Nos.52209108 and 52079034)Sichuan Science and Technology Program(Grant No.2023YFQ0021)+1 种基金the Natural Science Foundation of Heilongjiang Province,China(Grant No.LH2023E058)China Postdoctoral Science Foundation(Grant No.2022M720948)。
文摘Large-head variable-amplitude pump turbines(PTs) encounter serious transient hydraulic instability issues. To explore the evolution mechanisms of pressure fluctuations(PFs) and flow patterns inside large-head variable-amplitude PTs, the load rejection process(LRP) was investigated using a one-and three-dimensional coupled flow simulation approach. The temporal,spatial, and frequency characteristics of the fluctuating pressures were analyzed for four monitoring points using a combined time-frequency analysis approach. The results indicated that PFs during the LRP of large-head variable-amplitude PTs had a new fluctuation frequency component related to Dean vortices(DVs) in the volute, in addition to the common fluctuation frequency components related to rotor-stator interaction phenomena and local backflow vortices near the impeller inlet. The PF frequency component existed throughout the LRP and had a significant influence on the transient maximum pressure at the volute end. This study provides a useful theoretical guide for the design and optimization of large-head variable-amplitude PTs.
基金supported by the National Science and Technology Major Project,China(No.2017-III-0010-0036).
文摘The Secondary Air System(SAS)plays an important role in the safe operation and performance of aeroengines.The traditional 1D-3D coupling method loses information when used for secondary air systems,which affects the calculation accuracy.In this paper,a Cross-dimensional Data Transmission method(CDT)from 3D to 1D is proposed by introducing flow field uniformity into the data transmission.First,a uniformity index was established to quantify the flow field parameter distribution characteristics,and a uniformity index prediction model based on the locally weighted regression method(Lowess)was established to quickly obtain the flow field information.Then,an information selection criterion in 3D to 1D data transmission was established based on the Spearman rank correlation coefficient between the uniformity index and the accuracy of coupling calculation,and the calculation method was automatically determined according to the established criterion.Finally,a modified function was obtained by fitting the ratio of the 3D mass-average parameters to the analytical solution,which are then used to modify the selected parameters at the 1D-3D interface.Taking a typical disk cavity air system as an example,the results show that the calculation accuracy of the CDT method is greatly improved by a relative 53.88%compared with the traditional 1D-3D coupling method.Furthermore,the CDT method achieves a speedup of 2 to 3 orders of magnitude compared to the 3D calculation.