Motivated by improving the performance of particle-based Monte-Carlo simulations in the transitional regime, Fokker-Planck kinetic models have been devised and studied as approximations of the Boltzmann collision oper...
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Motivated by improving the performance of particle-based Monte-Carlo simulations in the transitional regime, Fokker-Planck kinetic models have been devised and studied as approximations of the Boltzmann collision operator. By generalizing the linear drift model, the cubic Fokker-Planck (cubic-FP) and ellipsoidal Fokker-Planck (ES-FP) have been proposed, in order to obtain the correct Prandtl number of 2/3 for a dilute monatomic gas. This study provides a close comparison between both models in low Mach and supersonic settings. While direct simulation Monte-Carlo (DSMC) here serves as the benchmark, overall close performance between cubic-FP, ES-FP, and DSMC is observed. Furthermore, while the ES-FP outperforms the cubic-FP model in the shock region of the supersonic flow around a cylinder, the latter shows a better accuracy in the near continuum regime. It is argued that the reason behind these discrepancies lies in the entropy law besides the transport properties.
One of the important issues in the assessment of intake/engine compatibility in civil turbofan engines is the prediction of the coupling effects between the intake and the engine. An actuator-disk model has been appli...
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One of the important issues in the assessment of intake/engine compatibility in civil turbofan engines is the prediction of the coupling effects between the intake and the engine. An actuator-disk model has been applied to the calculations of the flow through a high-bypass-ratio turbofan geometry, including the presence of the core-support pylon and a nonaxisymmetric inlet, and the effects of the core engine. The results of a series of calculations are presented, and the nature of the interactions between the flow through a fan and the system components is addressed.
The early stages of gas turbine combustor design represent a challenging combination of analytical analysis, numerical simulation, and rig testing. The objective of this work is the development of a versatile radiatio...
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The early stages of gas turbine combustor design represent a challenging combination of analytical analysis, numerical simulation, and rig testing. The objective of this work is the development of a versatile radiation submodel within the constraints of a preliminary gas turbine combustor simulation tool. A network approach forms the basis of the design solution algorithm, dividing the domain into a number of independent semiempirical interconnected subsections. A novel application of the pressure correction methodology more commonly employed by computational fluid dynamics codes is utilized to solve the combined continuity equation and pressure-drop/flow-rate relationships. A coupled conjugate heat transfer analysis is employed to determine heat transfer to the combustor liner. Radiation represents the most difficult mode of heat transfer to simulate in the combustor environment. A novel variation of the discrete transfer radiation model is presented and validated for use within the network solver. The effect of the radiation model on the prediction of liner wall temperature is evaluated in an annular gas turbine combustor at a typical high-power operating condition. The importance of radial distributions of temperature and soot are evaluated by examining the flametube wall heat transfer mechanism.
A computer code, VISCC, is developed to solve the three-dimensional, Reynolds-averaged, unsteady, compressible, and complete Navier-Stokes equations. The equations are solved by an implicit, fully vectorized, finite-v...
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A computer code, VISCC, is developed to solve the three-dimensional, Reynolds-averaged, unsteady, compressible, and complete Navier-Stokes equations. The equations are solved by an implicit, fully vectorized, finite-volume, upwind-biased, approximately factored, and multigrid method. A hybrid domain decomposition method is developed to utilize the combined advantages of overlapped grids, zonal grids, and block-structured grids. An algebraic turbulence model is developed to represent the Reynolds stresses. The store considered here for simulation is a missile configuration with four tail fins and an L-shaped offset sting. The missile is placed first directly above the opening of a rectangular box cavity, then submerged completely inside the cavity. These two cases represent two distinct and important interference characteristics for an internal store carriage and a subsequent separation. The freestream Mach and the unit Reynolds numbers are 2.75 and 2.97 million per foot, respectively. The results of the time-accurate computations depict these complex flows and help understanding the interference effects between the store and the cavity. These effects are more pronounced when the store is placed inside the parent body. The time-averaged surface pressures compare well with the wind-tunnel data.
This paper uses the bibliometric analysis software CiteSpace to examine the current status and evolution of cold-chain logistics vehicle routing problems(CCVRP).7381 relevant articles published in the Web of Science c...
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This paper uses the bibliometric analysis software CiteSpace to examine the current status and evolution of cold-chain logistics vehicle routing problems(CCVRP).7381 relevant articles published in the Web of Science core collection from 2008 to 2024 were analyzed,an in-depth understanding of the publication trends and category distribution were ***,CiteSpace was used to create a scientific knowledge graph and perform visualization *** analysis includes collaboration among authors,countries,and institutions;co-citation analysis of authors,journals,and references;citation burst detection of keywords;and co-citation cluster analysis of *** on a deep understanding of current research hotspots,an in-depth discussion of existing research was conducted from three perspectives:optimization objectives,distribution scenarios,and solution *** results show that CCVRP involves complex factors such as temperature requirements,time window constraints,and multi-objective *** intricate constraints are causing research to become increasingly interdisciplinary and *** evolution of hot topics shows that the research directions span multiple fields,from algorithm design to logistics *** review helps researchers better understand the history,current status,and future development directions of CCVRP research,and provides valuable references and inspiration for academia and practice.
Generalized primary/secondary flow equations are derived as an approximation to the Navier-Stokes equations for three-dimensional viscous flows with a dominant flow direction. The primary/secondary flow equations are ...
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Generalized primary/secondary flow equations are derived as an approximation to the Navier-Stokes equations for three-dimensional viscous flows with a dominant flow direction. The primary/secondary flow equations are well posed for solution by spatial marching and can be solved one to two orders of magnitude faster than the Navier-Stokes equations. A key element in the approximations, which is a distinguishing feature of the present approach, is that accuracy is related to curvature terms obtained from a local primary flow direction rather than the coordinate system used to describe geometry of the flowfield. Potential flow streamlines for the flow geometry under consideration are a suitable choice for the primary flow direction. A sequentially decoupled implicit algorithm has been developed that exploits the form of the primary/secondary flow equations to obtain decoupled subsets of equations through choices for dependent variables, the sequence of equations, and the linearization scheme. Each of the equation subsets is solved by efficient and appropriate implicit numerical procedures. Computed solutions for flow in 90-deg bends agree very well with experimental data and Navier-Stokes solutions. The combined efficiency and accuracy of the approximate equations and solution algorithm make this approach attractive for problems in which a suitable primary flow direction can be identified.
A three-dimensional space-marching algorithm using an unstructured discretization is proposed. The method utilizes a two-dimensional unstructured grid generator to construct grids in a crossflow plane while maintainin...
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A three-dimensional space-marching algorithm using an unstructured discretization is proposed. The method utilizes a two-dimensional unstructured grid generator to construct grids in a crossflow plane while maintaining structure in the marching direction. The spatial discretization is obtained by applying a characteristic-based, upwind, finite volume scheme for the solution of the Euler equations. solutions are presented for several different geometries comparing the results with existing numerical techniques and experiment.
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