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NIA Seminar by Andrea Dadone |
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Date: August 9, 2005
Time: 10:30am
Location: NIA, Rm 137
Rapid CFD Analysis and Design Using a Novel Cartesian Grid Formulation
Andrea Dadone, Politecnico di Bari, Italy
This talk addresses the development of a CFD tool that can compute reliable flow analyses suitable for use in the conceptional design process. Traditionally, early stages in aerodynamic design require detailed body-fitted grids over wide classes of different geometric topologies. Grid generation for complex topologies if often very laborious, and is not always as automated as desired and this becomes a major impediment to using CFD in design. One approach to address this issue has been to develop a simplified alternative to complex grid generation involving the use of Cartesian grid methods. In these methods the body does not coincide with grid surfaces or grid volume edges. Instead, the body is immersed in the grid and the complication of generating a body-fitted grid is exchanged for complications associated with the implementation of the surface boundary conditions.
The present research deals with the implementation of non-penetration boundary conditions at solid walls for inviscid flow computations on Cartesian grids. The crux of the method is a very accurate boundary condition implementation procedure (CCST) developed by Dadone and Grossman for body-fitted grids. The method introduces ghost cells near the boundaries whose flow values are developed from an assumed flow-field model in vicinity of the wall consisting of a vortex flow, with locally symmetric distribution of entropy and total enthalpy. In three dimensions this procedure is implemented in the so-called osculating plane. This method was shown to be substantially more accurate than traditional surface boundary condition approaches. This improved boundary condition is adapted to a Cartesian mesh formulation, which was called the Ghost-Cell Method. In this approach, all cell centers exterior to the body are computed with fluxes at the surrounding cell faces. Traditional Cartesian mesh approaches require the use of composite volume elements (cut cells) determined by the intersection of the grid and the body surface. The Ghost-Cell Method eliminates the need for cut cells and hence should be useful for broad classes of problems and flow solvers. The talk will contain comparison of the results of the method applied to relatively simple shapes including airfoils and wings in order to address the accuracy and efficacy of the approach. Applications to complex shapes will also be illustrated as well as a discussion of grid adaptation and design optimization.
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