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Coupled ordinates method for multigrid acceleration of radiation calculations

JOURNAL OF THERMOPHYSICS AND HEAT TRANSFER 1999年第4期13卷 467-473页

作者： Mathur, SR Murthy, JY Fluent Inc Lebanon NH 03766 USA Carnegie Mellon Univ Dept Mech Engn Pittsburgh PA 15213 USA

The finite volume and discrete ordinates methods are known to converge increasingly slowly as the optical thickness is increased. This is a result of the sequential nature of the solution procedure;the equations for energy and the directional intensities are solved one by one, assuming prevailing values for other variables. The coupled ordinates method is proposed whereby the discrete energy and intensity equations at each cell are solved simultaneously assuming spatial neighbors to be known. The point-coupled procedure is used as a relaxation sweep in a multigrid scheme. The formulation of coarse-level discrete equations admits arbitrary nonconvex polyhedra, making the scheme suitable for use with arbitrary unstructured polyhedral meshes. The scheme is shown to substantially accelerate convergence over a range of optical thicknesses.

关键词： Optical Thickness Energy Intensity Aspect Ratio Radiative Transfer Thermal Conductivity Numerical Integration Convection Radiation Heat Transfer solution algorithm Unstructured Grid

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Multiblock approach for calculating incompressible fluid flows on unstructured grids

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AIAA JOURNAL 1999年第2期37卷 169-176页

作者： Sheng, CH Whitfield, DL Anderson, WK Mississippi State Univ Natl Sci Fdn Engn Res Ctr Computat Fluid Dynam Lab Mississippi State MS 39762 USA NASA Langley Res Ctr Aerodynam & Acoust Methods Branch Fluid Mech & Acoust Div Hampton VA 23681 USA

A multiblock approach is presented for solving two-dimensional incompressible turbulent Bows on unstructured grids. The artificial compressibility form of the governing equations Is solved by a node-based, finite volume implicit scheme, which uses a backward Euler time discretization. Point Gauss-Seidel relaxations are used to solve the linear system of equations at each time step. A multiblock strategy to the solution procedure is introduced, which greatly improves the efficiency of the algorithm by significantly reducing the memory requirements while not increasing the CPU time, Results presented show that the current multiblock algorithm requires 73 % less memory than the single-block algorithm.

关键词： Unstructured Grid Compressibility Angle of Attack Reynolds Averaged Navier Stokes Turbulence Models solution algorithm NACA 4412 Domain Decomposition Methods Courant Friedrichs Lewy Freestream

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Finite volume discretization aspects for viscous flows on mixed unstructured grids

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AIAA JOURNAL 1999年第2期37卷 177-184页

作者： Haselbacher, A McGuirk, JJ Page, GJ Univ Loughborough Dept Aeronaut Engn Loughborough LE11 3TU Leics England

A solution method for compressible turbulent flows on unstructured grids in two dimensions is described. The method can be used on grids consisting of triangular and/or quadrilateral cells. Control volumes are constructed from dual cells, and the solution variables are stored at the vertices of the grid. Grid-transparent algorithms are developed that do not require knowledge of cell types, leading to simple discretization schemes on mixed grids. The inviscid fluxes are computed from limited high-resolution schemes originally developed for unstructured triangular grids. They are easily applied to quadrilateral or mixed grids and are grid transparent. The discretization of the viscous fluxes is studied in detail. A positive, grid-transparent discretization of Laplace's equation is developed, The existence of tangential derivatives in the viscous terms prevents grid transparency. By neglecting tangential derivatives, an approximate form of the viscous fluxes is developed, which recovers grid transparency. The approximate form is shown to be similar to the thin-shear-layer approximation. Results are obtained for a transonic inviscid flow, a laminar separated flow, and a transonic turbulent flow. Different control-volume constructions and quadrilateral, triangular, and mixed grids are assessed using a grid-refinement study. The approximate form of the viscous fluxes is investigated in detail.

关键词： Unstructured Grid Laplace Equation Shear Layers Viscous Flow NACA 0012 solution algorithm Eddy Viscosity Navier Stokes Equations Euler Equations Eddy Viscosity Turbulence Models

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Mean value analysis of military airlift operations at an individual airfield

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JOURNAL OF AIRCRAFT 1999年第5期36卷 750-755页

作者： Dietz, DC USAF Inst Technol Dept Operat Sci Wright Patterson AFB OH 45433 USA

An analytical queueing network model of airlift operations at an individual airfield is developed and implemented. The airfield system is represented as a capacitated open network of multiserver queues and fork-join constructs that capture concurrent aircraft flow through subnetworks of activities. Generated performance measures include mean values for system throughput, aircraft ground time, and resource utilizations, The quality of the analytical approximation is demonstrated through comparison with simulation results.

关键词： Airlift Airfields Aircraft on Ground Cumulative Distribution Function Air Mobility Command and Control Systems Software Development solution algorithm Aircraft Landing Air Forces

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Plastic analysis of complex microstructure composites using the generalized method of cells

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AIAA JOURNAL 1999年第4期37卷 482-488页

作者： Orozco, CE Pindera, MJ Univ Virginia Dept Civil Engn Charlottesville VA 22903 USA

A recently developed computationally efficient implementation of the Generalized Method of Cells is extended here to deal with plasticity problems. The new formulation can be used to perform linear elastic and plastic micromechanical analysis of composites with complex microstructures. It makes use of a tangent plasticity matrix approach as opposed to an initial stiffness matrix approach employed in the original Generalized Method of Cells. This tangent stiffness matrix approach makes it possible to perform plastic analyses of composites with microstructures that require a high-resolution, cell-subcell model. To demonstrate the capabilities of the new formulation, it is applied to the problem of determining the influence of fiber shape and fiber architecture on the plastic behavior of two-phase unidirectional composites. Some results from previous studies on this subject are confirmed. New results that could not be obtained with previous implementations are also reported. Problems modeled with up to 10,000 subcells are presented.

关键词： Microstructure Stiffness Matrices Plasticity Elastic Properties Residual Stress Material Properties Fiber Volume Fraction Aspect Ratio Boundary Value Problems solution algorithm

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Adaptive finite element solution of compressible turbulent flows

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AIAA JOURNAL 1998年第12期36卷 2187-2194页

作者： Ilinca, F Pelletier, D Ignat, L Natl Res Council Canada Inst Ind Mat Boucherville PQ Canada Ecole Polytech Dept Mech Engn Montreal PQ H3C 3A7 Canada

An adaptive finite element method for solving compressible turbulent Bows up to transonic regime is presented. Pressure-based methods previously developed for laminar compressible Bows and turbulent incompressible flows are combined to solve compressible turbulent Bows. Turbulence is incorporated via the k-epsilon model. The algorithm uses the logarithms of k and epsilon as computational variables to preserve positivity. solutions are obtained in primitive variables using quadratic finite elements on unstructured grids. The error is estimated by a local projection method. The solution algorithm and error estimation are validated on problems with known analytical solutions. The method is then applied to compressible subsonic and transonic Bows and predictions are compared with experimental measurements.

关键词： Transonic Flow Finite Element solution Compressibility Reynolds Averaged Navier Stokes Aerodynamics Turbulence Kinetic Energy solution algorithm Shear Layers Turbulence Models Computing

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Series load flow: A novel non-iterative load flow method

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IEE PROCEEDINGS-GENERATION TRANSMISSION AND DISTRIBUTION 1998年第3期145卷 251-256页

作者： Xu, W Liu, Y Salmon, JC Le, T Chang, GWK Univ Alberta Dept Elect & Comp Engn Edmonton AB T6G 2G7 Canada Virginia Polytech Inst & State Univ Dept Elect Engn Blacksburg VA 24061 USA ABB Power T&D Co Inc Raleigh NC 27606 USA Siemens Power T&D LLC Brooklyn Pk MN 55428 USA

A noniterative method for solving load flow equations is presented in the paper. The method is based on the Taylor series expansion of the inverse load flow function. Formulas to compute the Taylor series are derived and associated solution algorithms are developed, Load flow results can be obtained by simply calculating and summing the significant terms of the series. The proposed method is evaluated using four test systems. Potential applications of the method are discussed.

关键词： load flow Taylor series solution algorithm evaluation test systems

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Three-dimensional flow computation around a projectile overtaking a preceding shock wave

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JOURNAL OF SPACECRAFT AND ROCKETS 1998年第5期35卷 619-625页

作者： Watanabe, R Fujii, K Higashino, F Tokyo Noko Univ Dept Mech Syst Engn Tokyo Japan Inst Space & Astronaut Sci Kanagawa 229 Japan

A numerical simulation of the flowfield around a projectile overtaking a preceding shock wave is carried out by solving the three-dimensional, thin layer Navier-Stokes equations. A domain decomposition method with the fortified solution algorithm interface scheme is used to supply reasonable grid configurations for such an unsteady flowfield. Computed results show that complicated interaction flowfields are observed while overtaking the shock wave. The results of the two- and three-dimensional flowfield computations are compared, and the characteristic features of the three-dimensional flowfield are shown. Time histories of the aerodynamic forces show that the projectile suffers strong asymmetric forces while overtaking the shock wave, which may make the trajectory of the projectile unstable.

关键词： Conical Shock Wave Projectiles Aerodynamic Force Wake Vortices Navier Stokes Equations Adverse Pressure Gradient Boundary Layer Separation Domain Decomposition Methods solution algorithm Supersonic Speed

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Assessment of a radiative heat transfer model for gas turbine combustor preliminary design

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JOURNAL OF PROPULSION AND POWER 1998年第1期14卷 66-73页

作者： Stuttaford, PJ Rubini, PA Cranfield Univ Sch Mech Engn Bedford MK43 0AL England

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.

关键词： Gas Turbine Combustor Radiative Heat Transfer Annular Combustor Conjugate Heat Transfer Analysis Wall Temperature Continuity Equation Numerical Simulation solution algorithm Discrete Transfer Radiation Model Radiation Properties

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Damped oscillations of a liquid/gas surface upon step reduction in gravity

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JOURNAL OF SPACECRAFT AND ROCKETS 1997年第1期34卷 110-117页

作者： Wolk, G Dreyer, M Rath, HJ Weislogel, MM NASA LEWIS RES CTRMICROGRAV FLUIDS BRANCHCLEVELANDOH 44135

The reorientation and settling of a liquid/gas interface in a right circular cylinder upon step reduction in gravity is investigated numerically. A modified dynamic contact angle boundary condition is implemented where the hysteresis parameter gamma is employed as an adjustable parameter representing the degree of relative slip at the contact line. The effect of the boundary condition on the axial interface oscillation is studied and the dependence thereon of the resonant frequency and settling time is given. Results are shown regarding the behavior of the dynamic contact angle and the penetration of the surface oscillations into the bulk liquid. The numerical results are tuned via comparisons with existing experimental data, and a method for estimating the appropriate boundary condition providing good agreement is suggested. An accompanying scale analysis depicts gamma as a function of the Ohnesorge number, the cylinder radius, and the static contact angle, These independent parameters are measures of the system damping, characteristic surface deflection, and effective stiffness of the interface, Applications of the results may be made to spacecraft fluids management and the use of spacecraft and/or drop towers for fluids experimentation.

关键词： Ohnesorge Numbers Hysteresis Resonant Frequencies Capillary Number Surface Tension Navier Stokes Equations solution algorithm Propellant Linear Interpolation Numerical Analysis

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