The behavior of a jet discharged in the middle of a long line of jets in a coflowing environment was modeled using a hybrid approach. The integral and length-scale approaches were combined to model the dispersion of a...The behavior of a jet discharged in the middle of a long line of jets in a coflowing environment was modeled using a hybrid approach. The integral and length-scale approaches were combined to model the dispersion of a jet in a coflowing environment. As a typical length-scale model, the jet was divided into a number of distinct regimes in which a single parameter formed from a combination of the governing parameters dominates over the behaviour of a jet. In each of these regions we gave an integral solution which adequately describes the behavior of the jet. A set of length-scales was then defined for the transitions between each of the regions. It was found that the hybrid model could predict the velocity decay and radial growth of a jet as it moves downstream from the source and merges with ambient fluid in a coflowing environment. Comparisons computational results with the laboratory data for merging jet in a coflow indicate that the hybrid model predicts the behavior of the jet in each of the regimes well.展开更多
A three-dimensional mathematical model for calculating the steady flow of circular non-buoyant turbulent surface in a coflowing channel is presented in this paper. For closing the control equations, the k turbulence m...A three-dimensional mathematical model for calculating the steady flow of circular non-buoyant turbulent surface in a coflowing channel is presented in this paper. For closing the control equations, the k turbulence model is used in the mathematical model. The wall-function method is employed to treat the wall boundary condition at the bottom plane. The closed control equations are discretized by using Hybrid Finite Analytic Method (HFAM) on a non-uniform staggered grid system. The numerical results are obtained for different ratio of the jet velocity to the coflowing velocity. The comparison with experimental data shows good agreement.展开更多
This paper investigates the effects of coflow O2 level and temperature on diffusion flame of a CH4/H2 jet in hot coflow （JHC） from a burner system similar to that of Dally et al. The coflow O2 mass fraction （ Yo2 ...This paper investigates the effects of coflow O2 level and temperature on diffusion flame of a CH4/H2 jet in hot coflow （JHC） from a burner system similar to that of Dally et al. The coflow O2 mass fraction （ Yo2 ） is varied from 3% to 80% and the temperature （Tcof） from 1200 K to 1700 K. The Eddy Dissipation Concept （EDC） model with detailed reaction mechanisms GRI-Mech 3.0 is used for all simulations. To validate the modeling, several JHC flames are predicted under the experimental conditions of Dally et al. [Proc. Combust. Inst., 29 （1）, 1147-1154 （2002）] and the results obtained match well with the measurements. Results demonstrate that, when Yo2 decreased, the diffusion combustion is likely to transform from traditional combustion to MILD （Moderate or Intense Low-oxygen Dilution） combustion mode. When Tcof is higher, the temperature distribution over the whole domain trends to be more uniform. Reducing yo2 or Tcof leads to less production of intermediate species OH and CO. It is worth noting that if Yo2 is high enough （ Yo2 〉80%）, increasing Yo2 does not cause obvious temperature increase.展开更多
The effects of the velocity and width in coflow argon jet inlet on the flow characteristics of laminar argon thermal plasma jet flowing into the cold air have been studied by the large eddy simulation methods. The Kel...The effects of the velocity and width in coflow argon jet inlet on the flow characteristics of laminar argon thermal plasma jet flowing into the cold air have been studied by the large eddy simulation methods. The Kelvin–Helmholtz instability between argon thermal plasma jet and coflow argon jet causes the transition from a laminar jet to a turbulent jet in the presence of coflow argon jet. Moreover, increasing the velocity and width in coflow argon jet inlet can enhance turbulent transport and provoke coherent structure in the downstream of thermal plasma jet. And the mixing characteristics between argon thermal plasma, coflow argon and ambient air are strengthened. In addition, the width in coflow argon jet inlet has a significant effect on the distribution of temperature in the upstream of thermal plasma jet. It was also found that the transition occurs in advance with the increase of velocity and width in coflow argon jet inlet.展开更多
Experimental study on hydrodynamics and mass transfer efficiencyof jet coflow packing tray (JCPT) was conducted in a φ285 mm columnand φ200 mm column, respectively. Compared with new vertical sievetray which has bee...Experimental study on hydrodynamics and mass transfer efficiencyof jet coflow packing tray (JCPT) was conducted in a φ285 mm columnand φ200 mm column, respectively. Compared with new vertical sievetray which has been applied in the petrochemical industry since 1968,the JCPT has lower pressure drop, higher capacity and higher masstransfer efficiency, and seems promising in commercial application.展开更多
Cloud data centers, such as Amazon EC2, host myriad big data applications using Virtual Machines(VMs). As these applications are communication-intensive, optimizing network transfer between VMs is critical to the perf...Cloud data centers, such as Amazon EC2, host myriad big data applications using Virtual Machines(VMs). As these applications are communication-intensive, optimizing network transfer between VMs is critical to the performance of these applications and network utilization of data centers. Previous studies have addressed this issue by scheduling network flows with coflow semantics or optimizing VM placement with traffic considerations.However, coflow scheduling and VM placement have been conducted orthogonally. In fact, these two mechanisms are mutually dependent, and optimizing these two complementary degrees of freedom independently turns out to be suboptimal. In this paper, we present VirtCO, a practical framework that jointly schedules coflows and places VMs ahead of VM launch to optimize the overall performance of data center applications. We model the joint coflow scheduling and VM placement optimization problem, and propose effective heuristics for solving it. We further implement VirtCO with OpenStack and deploy it in a testbed environment. Extensive evaluation of real-world traces shows that compared with state-of-the-art solutions, VirtCO greatly reduces the average coflow completion time by up to 36.5%. This new framework is also compatible with and readily deployable within existing data center architectures.展开更多
With the continuous enrichment of cloud services, an increasing number of applications are being deployed in data centers. These emerging applications are often communication-intensive and data-parallel, and their per...With the continuous enrichment of cloud services, an increasing number of applications are being deployed in data centers. These emerging applications are often communication-intensive and data-parallel, and their performance is closely related to the underlying network. With their distributed nature, the applications consist of tasks that involve a collection of parallel flows. Traditional techniques to optimize flow-level metrics are agnostic to task-level requirements, leading to poor application-level performance. In this paper, we address the heterogeneous task-level requirements of applications and propose task-aware flow scheduling. First, we model tasks' sensitivity to their completion time by utilities. Second, on the basis of Nash bargaining theory, we establish a flow scheduling model with heterogeneous utility characteristics, and analyze it using Lagrange multiplier method and KKT condition. Third, we propose two utility-aware bandwidth allocation algorithms with different practical constraints. Finally, we present Tasch, a system that enables tasks to maintain high utilities and guarantees the fairness of utilities. To demonstrate the feasibility of our system, we conduct comprehensive evaluations with realworld traffic trace. Communication stages complete up to 1.4 faster on average, task utilities increase up to 2.26,and the fairness of tasks improves up to 8.66 using Tasch in comparison to per-flow mechanisms.展开更多
文摘The behavior of a jet discharged in the middle of a long line of jets in a coflowing environment was modeled using a hybrid approach. The integral and length-scale approaches were combined to model the dispersion of a jet in a coflowing environment. As a typical length-scale model, the jet was divided into a number of distinct regimes in which a single parameter formed from a combination of the governing parameters dominates over the behaviour of a jet. In each of these regions we gave an integral solution which adequately describes the behavior of the jet. A set of length-scales was then defined for the transitions between each of the regions. It was found that the hybrid model could predict the velocity decay and radial growth of a jet as it moves downstream from the source and merges with ambient fluid in a coflowing environment. Comparisons computational results with the laboratory data for merging jet in a coflow indicate that the hybrid model predicts the behavior of the jet in each of the regimes well.
文摘A three-dimensional mathematical model for calculating the steady flow of circular non-buoyant turbulent surface in a coflowing channel is presented in this paper. For closing the control equations, the k turbulence model is used in the mathematical model. The wall-function method is employed to treat the wall boundary condition at the bottom plane. The closed control equations are discretized by using Hybrid Finite Analytic Method (HFAM) on a non-uniform staggered grid system. The numerical results are obtained for different ratio of the jet velocity to the coflowing velocity. The comparison with experimental data shows good agreement.
基金Supported by the National Natural Science Foundation of China （51276002）, and the Specific Research Fund for the Doctoral Program of Higher Education of China （20110001130014）.
文摘This paper investigates the effects of coflow O2 level and temperature on diffusion flame of a CH4/H2 jet in hot coflow （JHC） from a burner system similar to that of Dally et al. The coflow O2 mass fraction （ Yo2 ） is varied from 3% to 80% and the temperature （Tcof） from 1200 K to 1700 K. The Eddy Dissipation Concept （EDC） model with detailed reaction mechanisms GRI-Mech 3.0 is used for all simulations. To validate the modeling, several JHC flames are predicted under the experimental conditions of Dally et al. [Proc. Combust. Inst., 29 （1）, 1147-1154 （2002）] and the results obtained match well with the measurements. Results demonstrate that, when Yo2 decreased, the diffusion combustion is likely to transform from traditional combustion to MILD （Moderate or Intense Low-oxygen Dilution） combustion mode. When Tcof is higher, the temperature distribution over the whole domain trends to be more uniform. Reducing yo2 or Tcof leads to less production of intermediate species OH and CO. It is worth noting that if Yo2 is high enough （ Yo2 〉80%）, increasing Yo2 does not cause obvious temperature increase.
基金supported by National Natural Science Foundation of China(Nos.12035015 and 12105282)。
文摘The effects of the velocity and width in coflow argon jet inlet on the flow characteristics of laminar argon thermal plasma jet flowing into the cold air have been studied by the large eddy simulation methods. The Kelvin–Helmholtz instability between argon thermal plasma jet and coflow argon jet causes the transition from a laminar jet to a turbulent jet in the presence of coflow argon jet. Moreover, increasing the velocity and width in coflow argon jet inlet can enhance turbulent transport and provoke coherent structure in the downstream of thermal plasma jet. And the mixing characteristics between argon thermal plasma, coflow argon and ambient air are strengthened. In addition, the width in coflow argon jet inlet has a significant effect on the distribution of temperature in the upstream of thermal plasma jet. It was also found that the transition occurs in advance with the increase of velocity and width in coflow argon jet inlet.
文摘Experimental study on hydrodynamics and mass transfer efficiencyof jet coflow packing tray (JCPT) was conducted in a φ285 mm columnand φ200 mm column, respectively. Compared with new vertical sievetray which has been applied in the petrochemical industry since 1968,the JCPT has lower pressure drop, higher capacity and higher masstransfer efficiency, and seems promising in commercial application.
基金supported by the National Key R&D Program of China(No.2017YFB1003000)the National Natural Science Foundation of China(Nos.61572129,61602112,61502097,61702096,61320106007,and 61632008)+4 种基金the International S&T Cooperation Program of China(No.2015DFA10490)the National Science Foundation of Jiangsu Province(Nos.BK20160695 and BK20170689)the Jiangsu Provincial Key Laboratory of Network and Information Security(No.BM2003201)the Key Laboratory of Computer Network and InformationIntegration of Ministry of Education of China(No.93K-9)supported by the Collaborative Innovation Center of Novel Software Technology and Industrialization and Collaborative Innovation Center of Wireless Communications Technology
文摘Cloud data centers, such as Amazon EC2, host myriad big data applications using Virtual Machines(VMs). As these applications are communication-intensive, optimizing network transfer between VMs is critical to the performance of these applications and network utilization of data centers. Previous studies have addressed this issue by scheduling network flows with coflow semantics or optimizing VM placement with traffic considerations.However, coflow scheduling and VM placement have been conducted orthogonally. In fact, these two mechanisms are mutually dependent, and optimizing these two complementary degrees of freedom independently turns out to be suboptimal. In this paper, we present VirtCO, a practical framework that jointly schedules coflows and places VMs ahead of VM launch to optimize the overall performance of data center applications. We model the joint coflow scheduling and VM placement optimization problem, and propose effective heuristics for solving it. We further implement VirtCO with OpenStack and deploy it in a testbed environment. Extensive evaluation of real-world traces shows that compared with state-of-the-art solutions, VirtCO greatly reduces the average coflow completion time by up to 36.5%. This new framework is also compatible with and readily deployable within existing data center architectures.
基金supported by the National Key R&D Program of China(No.2017YFB1003000)the National Natural Science Foundation of China(Nos.61872079,61572129,61602112,61502097,61702096,61320106007,61632008,and 61702097)+4 种基金the Natural Science Foundation of Jiangsu Province(Nos.BK20160695 and BK20170689)the Fundamental Research Funds for the Central Universities(No.2242018k1G019)the Jiangsu Provincial Key Laboratory of Network and Information Security(No.BM2003201)the Key Laboratory of Computer Network and Information Integration of Ministry of Education of China(No.93K-9)partially supported by the Collaborative Innovation Center of Novel Software Technology and Industrialization and Collaborative Innovation Center of Wireless Communications Technology
文摘With the continuous enrichment of cloud services, an increasing number of applications are being deployed in data centers. These emerging applications are often communication-intensive and data-parallel, and their performance is closely related to the underlying network. With their distributed nature, the applications consist of tasks that involve a collection of parallel flows. Traditional techniques to optimize flow-level metrics are agnostic to task-level requirements, leading to poor application-level performance. In this paper, we address the heterogeneous task-level requirements of applications and propose task-aware flow scheduling. First, we model tasks' sensitivity to their completion time by utilities. Second, on the basis of Nash bargaining theory, we establish a flow scheduling model with heterogeneous utility characteristics, and analyze it using Lagrange multiplier method and KKT condition. Third, we propose two utility-aware bandwidth allocation algorithms with different practical constraints. Finally, we present Tasch, a system that enables tasks to maintain high utilities and guarantees the fairness of utilities. To demonstrate the feasibility of our system, we conduct comprehensive evaluations with realworld traffic trace. Communication stages complete up to 1.4 faster on average, task utilities increase up to 2.26,and the fairness of tasks improves up to 8.66 using Tasch in comparison to per-flow mechanisms.
