Developments and trends in three-dimensional mesh generation

An intense research effort over the last few years has produced several competing and apparently diverse methods for generating meshes. Recent progress is reviewed and the central themes are emphasized which form a solid foundation for future developments in mesh generation

High-order Discretization of a Gyrokinetic Vlasov Model in Edge Plasma Geometry

We present a high-order spatial discretization of a continuum gyrokinetic Vlasov model in axisymmetric tokamak edge plasma geometries. Such models describe the phase space advection of plasma species distribution functions in the absence of collisions. The gyrokinetic model is posed in a four-dimensional phase space, upon which a grid is imposed when discretized. To mitigate the computational cost associated with high-dimensional grids, we employ a high-order discretization to reduce the grid size needed to achieve a given level of accuracy relative to lower-order methods. Strong anisotropy induced by the magnetic field motivates the use of mapped coordinate grids aligned with magnetic flux surfaces. The natural partitioning of the edge geometry by the separatrix between the closed and open field line regions leads to the consideration of multiple mapped blocks, in what is known as a mapped multiblock (MMB) approach. We describe the specialization of a more general formalism that we have developed for the construction of high-order, finite-volume discretizations on MMB grids, yielding the accurate evaluation of the gyrokinetic Vlasov operator, the metric factors resulting from the MMB coordinate mappings, and the interaction of blocks at adjacent boundaries. Our conservative formulation of the gyrokinetic Vlasov model incorporates the fact that the phase space velocity has zero divergence, which must be preserved discretely to avoid truncation error accumulation. We describe an approach for the discrete evaluation of the gyrokinetic phase space velocity that preserves the divergence-free property to machine precision

Towards Automatic Multiblock Topology Generation. G.U. Aero Report 9826

The need for automation of the multiblock grid generation process is discussed. A new approach to automatically process a multiblock topology in order to prepare it for the grid generation process is described. The method is based on a cost function which attempts to model the objectives of the skilled grid generation software user who at present performs the task of block positioning and shaping in an interactive manner. A number of test cases are examined. It is also suggested that an existing unstructured mesh generation method could be adopted as an initial topology generation tool. Further work towards creating a fully automatic grid generation tool and extension into three dimensions are discussed briefly

Institute for Computational Mechanics in Propulsion (ICOMP)

The Institute for Computational Mechanics in Propulsion (ICOMP) is a combined activity of Case Western Reserve University, Ohio Aerospace Institute (OAI) and NASA Lewis. The purpose of ICOMP is to develop techniques to improve problem solving capabilities in all aspects of computational mechanics related to propulsion. The activities at ICOMP during 1991 are described

Velocity-pressure coupling in finite difference formulations for the Navier-Stokes equations

A new numerical algorithm for solving the two-dimensional, steady, incompressible, laminar, viscous flow equations on a staggered grid is presented in this thesis. The proposed methodology is finite difference based, but essentially takes advantage of the best features of two well-established numerical formulations, the finite difference and finite volume methods. Some weaknesses of the finite difference approach are removed by exploiting the strengths of the finite volume method. In particular, the issue of velocity-pressure coupling is dealt with in the proposed finite difference formulation by developing a new pressure correction equation in a manner similar to the SIMPLE (Semi-Implicit Method for Pressure Linked Equations) approach commonly used in finite volume formulations. However, since this is purely a finite difference formulation, numerical approximation of fluxes is not required. Results obtained from the present method are based on the first-order upwind differencing scheme for the convective terms, but the methodology can easily be modified to accommodate higher order differencing schemes. Comparison with exact solutions for flow in a straight duct is made. The new formulation is also validated against experimental and other numerical data for well-known benchmark problems, namely the lid-driven cavity and backward-facing step flows. For curvilinear domains, the proposed method is validated against numerical results for a complex channel flow and compared to experimental results for the flow over a scour hole. For further validation, some of the results from the present method are compared to results obtained by FLUENT.Dept. of Mathematics and Statistics. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis2006 .Z64. Source: Dissertation Abstracts International, Volume: 67-07, Section: B, page: 3842. Thesis (Ph.D.)--University of Windsor (Canada), 2006

Progress Report: Application of the Multiblock Method in Computational Aerodynamics. Aero Report 9621

This report serves as a record of the progress made since October 1995 as a postgraduate research student smdying in the field of computational aerodynamics. The area of interest is the application of the multiblock method to examine real problems in aerodynamics. The experience gained in using various multiblock grid generation packages is discussed, along with an examination of the load balancing problem for parallel execution of aerodynamic flow solvers. Some initial results from the development of a static load balancer based on the method of simulated annealing are presented

A simple procedure for generating locally refined 2D quadrilateral finite element meshes of gears

This article describes a new procedure for automated generation of two-dimensional locally refined quadrilateral meshes of gear drives. In this new procedure, a base mesh is generated using a multiblock meshing procedure. Then, selected elements of the base mesh are subdivided to obtain a refined mesh in certain parts of the gear teeth. The proposed procedure is completed with a mesh quality enhancement technique, which is based on an optimization-based smoothing. It also includes strategies that allow to automatically identify and refine those areas of the gear that are typically subjected to elevated stress gradients. The performance of the proposed procedure is illustrated with numerical examples, and it is compared to other existing meshing procedures, both in terms of mesh distortion and accuracy of the results

High-Performance Parallel Analysis of Coupled Problems for Aircraft Propulsion

Applications are described of high-performance computing methods to the numerical simulation of complete jet engines. The methodology focuses on the partitioned analysis of the interaction of the gas flow with a flexible structure and with the fluid mesh motion driven by structural displacements. The latter is treated by a ALE technique that models the fluid mesh motion as that of a fictitious mechanical network laid along the edges of near-field elements. New partitioned analysis procedures to treat this coupled three-component problem were developed. These procedures involved delayed corrections and subcycling, and have been successfully tested on several massively parallel computers, including the iPSC-860, Paragon XP/S and the IBM SP2. The NASA-sponsored ENG10 program was used for the global steady state analysis of the whole engine. This program uses a regular FV-multiblock-grid discretization in conjunction with circumferential averaging to include effects of blade forces, loss, combustor heat addition, blockage, bleeds and convective mixing. A load-balancing preprocessor for parallel versions of ENG10 was developed as well as the capability for the first full 3D aeroelastic simulation of a multirow engine stage. This capability was tested on the IBM SP2 parallel supercomputer at NASA Ames