In this paper, the periodically unsteady pressure field and head-drop phenomenon caused by leading edge cavitation have been investigated numerically by computational fluid dynamics （CFD） in a single stage centrifug...In this paper, the periodically unsteady pressure field and head-drop phenomenon caused by leading edge cavitation have been investigated numerically by computational fluid dynamics （CFD） in a single stage centrifugal pump. A CFD model for cavita- tion steady and unsteady simulation has been calculated using the κ-ω SST turbulence model combining with a multiphase ap- proach, based on a homogeneous model assumption. A truncated form of Rayleigh-Plesset equation is used as a source term for the inter-phase mass transfer. The CFD computational region includes the suction cone, impeller, side chambers and volute, as well as suction and pressure pipes. The results were compared with experimental data under non-cavitation and cavitation conditions and a good agreement was obtained for the global performance, the experimental data of the head and the efficiency are 34.04 m and 74.42% at BEP, respectively, the predicted head is 34.31 m and the predicted efficiency is 73.75%. The analy- sis of inner flow pattern shows that the vortex flow generation in the rear of cavity region is the main reason of the head-drop. Obvious increasing can be observed for the amplitude of the pressure fluctuation at the blade passing frequency with different cavitation situations, and subpeak can be found. Besides, the effects of unsteady flow in the side chambers cannot be neglected for accurately predicting the inner flow of the pump. These results imply that this numerical method is suitable for the cavitat- ing flow in the pump.展开更多
This paper expounds the basic principles and structures of the whole petroleum system to reveal the pattern of conventional oil/gas-tight oil/gas-shale oil/gas sequential accumulation and the hydrocarbon accumulation ...This paper expounds the basic principles and structures of the whole petroleum system to reveal the pattern of conventional oil/gas-tight oil/gas-shale oil/gas sequential accumulation and the hydrocarbon accumulation models and mechanisms of the whole petroleum system.It delineates the geological model,flow model,and production mechanism of shale and tight reservoirs,and proposes future research orientations.The main structure of the whole petroleum system includes three fluid dynamic fields,three types of oil and gas reservoirs/resources,and two types of reservoir-forming processes.Conventional oil/gas,tight oil/gas,and shale oil/gas are orderly in generation time and spatial distribution,and sequentially rational in genetic mechanism,showing the pattern of sequential accumulation.The whole petroleum system involves two categories of hydrocarbon accumulation models:hydrocarbon accumulation in the detrital basin and hydrocarbon accumulation in the carbonate basin/formation.The accumulation of unconventional oil/gas is self-containment,which is microscopically driven by the intermolecular force(van der Waals force).The unconventional oil/gas production has proved that the geological model,flow model,and production mechanism of shale and tight reservoirs represent a new and complex field that needs further study.Shale oil/gas must be the most important resource replacement for oil and gas resources of China.Future research efforts include:(1)the characteristics of the whole petroleum system in carbonate basins and the source-reservoir coupling patterns in the evolution of composite basins;(2)flow mechanisms in migration,accumulation,and production of shale oil/gas and tight oil/gas;(3)geological characteristics and enrichment of deep and ultra-deep shale oil/gas,tight oil/gas and coalbed methane;(4)resource evaluation and new generation of basin simulation technology of the whole petroleum system;(5)research on earth system-earth organic rock and fossil fuel system-whole petroleum system.展开更多
The genus Macaca serves as an ideal research model for speciation and introgressive gene flow due to its short period of diversification(about five million years ago)and rapid radiation of constituent species.To under...The genus Macaca serves as an ideal research model for speciation and introgressive gene flow due to its short period of diversification(about five million years ago)and rapid radiation of constituent species.To understand evolutionary gene flow in macaques,we sequenced four whole genomes(two M.arctoides and two M.thibetana)and combined them with publicly available macaque genome data for genome-wide analyses.We analyzed 14 individuals from nine Macaca species covering all Asian macaque species groups and detected extensive gene flow signals,with the strongest signals between the fascicularis and silenus species groups.Notably,we detected bidirectional gene flow between M.fascicularis and M.nemestrina.The estimated proportion of the genome inherited via gene flow between the two species was 6.19%.However,the introgression signals found among studied island species,such as Sulawesi macaques and M.fuscata,and other species were largely attributed to the genomic similarity of closely related species or ancestral introgression.Furthermore,gene flow signals varied in individuals of the same species(M.arctoides,M.fascicularis,M.mulatta,M.nemestrina and M.thibetana),suggesting very recent gene flow after the populations split.Pairwise sequentially Markovian coalescence(PSMC)analysis showed all macaques experienced a bottleneck five million years ago,after which different species exhibited different fluctuations in demographic history trajectories,implying they have experienced complicated environmental variation and climate change.These results should help improve our understanding of the complicated evolutionary history of macaques,particularly introgressive gene flow.展开更多
基金supported by the State Key Program of National Natural Science Foundation of China (Grant No. 51239005)the National Science & Technology Pillar Program (Grant No. 2011BAF14B04)the Jiangsu Provincial Project for Innovative Postgraduates of China (Grant No. CXZZ11_0564)
文摘In this paper, the periodically unsteady pressure field and head-drop phenomenon caused by leading edge cavitation have been investigated numerically by computational fluid dynamics （CFD） in a single stage centrifugal pump. A CFD model for cavita- tion steady and unsteady simulation has been calculated using the κ-ω SST turbulence model combining with a multiphase ap- proach, based on a homogeneous model assumption. A truncated form of Rayleigh-Plesset equation is used as a source term for the inter-phase mass transfer. The CFD computational region includes the suction cone, impeller, side chambers and volute, as well as suction and pressure pipes. The results were compared with experimental data under non-cavitation and cavitation conditions and a good agreement was obtained for the global performance, the experimental data of the head and the efficiency are 34.04 m and 74.42% at BEP, respectively, the predicted head is 34.31 m and the predicted efficiency is 73.75%. The analy- sis of inner flow pattern shows that the vortex flow generation in the rear of cavity region is the main reason of the head-drop. Obvious increasing can be observed for the amplitude of the pressure fluctuation at the blade passing frequency with different cavitation situations, and subpeak can be found. Besides, the effects of unsteady flow in the side chambers cannot be neglected for accurately predicting the inner flow of the pump. These results imply that this numerical method is suitable for the cavitat- ing flow in the pump.
基金Supported by the National Natural Science Foundation of China(U22B6002)PetroChina Science Research and Technology Development Project(2021DJ0101)。
文摘This paper expounds the basic principles and structures of the whole petroleum system to reveal the pattern of conventional oil/gas-tight oil/gas-shale oil/gas sequential accumulation and the hydrocarbon accumulation models and mechanisms of the whole petroleum system.It delineates the geological model,flow model,and production mechanism of shale and tight reservoirs,and proposes future research orientations.The main structure of the whole petroleum system includes three fluid dynamic fields,three types of oil and gas reservoirs/resources,and two types of reservoir-forming processes.Conventional oil/gas,tight oil/gas,and shale oil/gas are orderly in generation time and spatial distribution,and sequentially rational in genetic mechanism,showing the pattern of sequential accumulation.The whole petroleum system involves two categories of hydrocarbon accumulation models:hydrocarbon accumulation in the detrital basin and hydrocarbon accumulation in the carbonate basin/formation.The accumulation of unconventional oil/gas is self-containment,which is microscopically driven by the intermolecular force(van der Waals force).The unconventional oil/gas production has proved that the geological model,flow model,and production mechanism of shale and tight reservoirs represent a new and complex field that needs further study.Shale oil/gas must be the most important resource replacement for oil and gas resources of China.Future research efforts include:(1)the characteristics of the whole petroleum system in carbonate basins and the source-reservoir coupling patterns in the evolution of composite basins;(2)flow mechanisms in migration,accumulation,and production of shale oil/gas and tight oil/gas;(3)geological characteristics and enrichment of deep and ultra-deep shale oil/gas,tight oil/gas and coalbed methane;(4)resource evaluation and new generation of basin simulation technology of the whole petroleum system;(5)research on earth system-earth organic rock and fossil fuel system-whole petroleum system.
基金supported by the National Natural Science Foundation of China(31530068,31770415)Fundamental Research Funds for the Central Universities(SCU2021D006)。
文摘The genus Macaca serves as an ideal research model for speciation and introgressive gene flow due to its short period of diversification(about five million years ago)and rapid radiation of constituent species.To understand evolutionary gene flow in macaques,we sequenced four whole genomes(two M.arctoides and two M.thibetana)and combined them with publicly available macaque genome data for genome-wide analyses.We analyzed 14 individuals from nine Macaca species covering all Asian macaque species groups and detected extensive gene flow signals,with the strongest signals between the fascicularis and silenus species groups.Notably,we detected bidirectional gene flow between M.fascicularis and M.nemestrina.The estimated proportion of the genome inherited via gene flow between the two species was 6.19%.However,the introgression signals found among studied island species,such as Sulawesi macaques and M.fuscata,and other species were largely attributed to the genomic similarity of closely related species or ancestral introgression.Furthermore,gene flow signals varied in individuals of the same species(M.arctoides,M.fascicularis,M.mulatta,M.nemestrina and M.thibetana),suggesting very recent gene flow after the populations split.Pairwise sequentially Markovian coalescence(PSMC)analysis showed all macaques experienced a bottleneck five million years ago,after which different species exhibited different fluctuations in demographic history trajectories,implying they have experienced complicated environmental variation and climate change.These results should help improve our understanding of the complicated evolutionary history of macaques,particularly introgressive gene flow.
