O. Hassan

UNSTRUCTURED TETRAHEDRAL MESH GENERATION FOR THREE-DIMENSIONAL VISCOUS FLOWS

A method of generating general tetrahedral meshes suitable for use in viscous flow simulations is proposed. The approach which is followed consists of the initial generation of a number of unstructured layers of highly stretched elements, in the vicinity of solid walls, followed by the discretisation of the remainder of the domain, by a standard advancing front procedure. The numerical performance of the proposed methodology is demonstrated by the generation of meshes suitable for viscous flow analysis over a number of three-dimensional aerodynamic configurations of current practical interest.

The computation of three-dimensional flows using unstructured grids

Abstract A general method is described for automatically discretising, into unstructured assemblies of tetrahedra, the three-dimensional solution domains of complex shape which are of interest in practical computational aerodynamics. An algorithm for the solution of the compressible Euler equations which can be implemented on such general unstructured tetrahedral grids is described. This is an explicit cell-vertex scheme which follows a general Taylor-Galerkin philosophy. The approach is employed to compute a transonic inviscid flow over a standard wing and the results are shown to compare favourably with experimental observations. As a more practical demonstration, the method is then applied to the analysis of inviscid flow over a complete modern fighter configuration. The effect of using mesh adaptivity is illustrated when the method is applied to the solution of high speed flow in an engine inlet.

Parallel processing for the simulation of problems involving scattering of electromagnetic waves

Abstract The three-dimensional simulation of the scattering of electromagnetic waves by obstacles of arbitrary geometrical shape is considered. Maxwells curl equations are solved in the time domain on an unstructured mesh of linear tetrahedral elements. The discrete equations are formed by a Galerkin procedure, with a Lax-Wendroff consistent numerical flux function and explicit time stepping. Parallelisation of the procedure is achieved by mesh decomposition and the use of a single program multiple data model. The approach is first validated and is then applied to problems involving the scattering of plane electromagnetic waves by a complete aircraft.

A time domain unstructured grid approach to the simulation of electromagnetic scattering in piecewise homogeneous media

Abstract The simulation of the scattering of plane electromagnetic waves by obstacles constructed from piecewise homogeneous material media is considered. The governing equations are Maxwells equations, which are expressed in a conservation form. The solution is obtained on a grid consisting of an unstructured assembly of linear triangular elements in 2D, by modifying a technique developed originally for the solution of the compressible Euler equations. The computed solution is used to determine the radar scattering width of the obstacle.

UNSTRUCTURED MESH PROCEDURES FOR THE SIMULATION OF THREE-DIMENSIONAL TRANSIENT COMPRESSIBLE INVISCID FLOWS WITH MOVING BOUNDARY COMPONENTS

SUMMARY The solution of high-speed transient inviscid compressible flow problems in three dimensions is considered. Discretization of the spatial domain is accomplished by the use of tetrahedral elements generated by Delaunay triangulation with automatic point creation. Methods of adapting the mesh to allow for boundary movement are considered and a strategy for ensuring boundary recovery is proposed. An explicit multistage time-stepping algorithm is employed to advance the flow solution. A number of examples are included to illustrate the numerical performance of the proposed procedures. # 1998 John Wiley & Sons, Ltd. Int. J. Numer. Meth. Fluids, 27: 41‐55 (1998)

A parallel framework for multidisciplinary aerospace engineering simulations using unstructured meshes

High performance parallel computers offer the promise of sufficient computational power to enable the routine use of large scale simulations during the process of engineering design. With this in mind, and with particular reference to the aerospace industry, this paper describes developments that have been undertaken to provide parallel implementations of algorithms for simulation, mesh generation and visualization. Designers are also demanding that software should be easy to use and, here, this requirement is addressed by embedding the algorithms within a convenient computer environment. This environment allows for the integration of arbitrary application software, which enables the development of a multidisciplinary engineering analysis capability within a unified computational framework

An implicit/explicit scheme for compressible viscous high speed flows

Abstract An implicit/explicit finite element based algorithm for the solution of 2D steady compressible viscous high speed flows is presented. A structured grid is employed in the vicinity of solid walls and the implicit form of the algorithm is implemented in this region. The explicit form of the algorithm is used in the remainder of the flow domain, which is discretised with an unstructured assembly of triangles. The quality of the computed solution is improved by the application of solution adaptive remeshing. The computed results for two examples are compared with experimental observations to illustrate the performance of the proposed scheme.

Turbulent flow computations on 3D unstructured grids

Abstract An edge-based finite element method is presented for the simulation of compressible turbulent flows on unstructured tetrahedral grids. A two equation k – ω turbulence model is employed and the standard Galerkin approach is used for spatial discretisation. Stabilisation of the resulting procedure is achieved by the addition of an appropriate diffusion. An explicit multistage time-stepping scheme is used to advance the solution in time to steady state. The performance of the algorithm is demonstrated for the simulation of a high Reynolds number transonic separated flow over a wing.

Compressible flowfield solutions with unstructured grids generated by Delaunay triangulation

A method is described that constructs three-dimensional unstructured tetrahedral meshes using the Delaunay triangulation criterion. The approach includes an automatic point creation technique and ensures that, given an initial surface triangulation which bounds a domain, a valid boundary conforming assembly of tetrahedra is produced. The efficiency of the proposed procedure reduces the computer time for the generation of realistic unstructured tetrahedral grids to the order of minutes on workstations of modest computational capabilities. The grids generated are used with two finite element algorithms to simulate inviscid transonic compressible flows. Flow solutions for aerospace configurations are presented and computed results compared with experimental data.

The adaptation of unstructured grids for transonic viscous flow simulation

Abstract The computation of viscous flows using unstructured grids is a relatively new area of research. This paper details work carried out to analyse the efficiency of initial unstructured viscous grids and their adaptation, particularly in the region of aerofoil trailing edges. This will enable an optimal approach to be established which can be extended into practical three-dimensional viscous flow simulations.