A multi-block boundary element method for CFD/CSD grid interfacing

Abstract

A three-dimensional (3-D) Indirect Boundary Element Method (IBEM) approach with a multi-block capability has been developed for Computational Fluid Dynamics (CFD) and Computational Structural Dynamics (CSD) grid interfacing. Formulating the data transferal problem as an equivalent solid mechanics problem, the IBEM approach generates a universal spline matrix that can be used for both displacement and force transferal Because its computational procedure does not require the information of the CFD grid connectivity, the IBEM approach can handle any types of CFD mesh including structured, unstructured and overset grids. The multi-block capability enables the IBEM approach to deal with complex configuration including structural discontinuity like control surfaces. Three test cases are shown to demonstrate the accuracy, efficiency and effectiveness of the IBEM approach for the CFD/CSD grid interfacing problem. Introduction Aeroelastic analysis, as an interdisciplinary problem, requires the coupling of the aerodynamic and structural responses. In practice, the requirements to generate the discretized models of these disciplines are subject to different engineering considerations. The grid system of a discretized aerodynamic model is usually placed on the external surface, whereas that of a structural model on internal load-carry components. This gives rise to the interfacing problem of transferring the computed data between these two grid systems. This interfacing problem usually amounts to the transferal of the displacements computed in the structural grid to the aerodynamic grid, and that of loads from the aerodynamic grid to the structural grid. To develop a suitable methodology for solving this type of interfacing problem is by no means a trivial task. Such a methodology is paramount as demanded by the improved resolution of high-level Computational Fluid Dynamics (CFD) and Computational Structural Dynamics (CSD) methods. Currently, the most widely used methods for the above data transferal problem are the Infinite Plate Spline (IPS, Ref 1) method and the Thin Plate Spline (TPS, Ref 2) methods. The IPS method is formulated based on an infinite plate solution and, therefore, is T Vice President pc@zonatech.com, (480)945-9988 * Research Associate xwgao@imapl .asu.edu, (480)965-4803 Copyright © 2000 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. suitable only for lifting surface aerodynamic method such as the Double Lattice method and Harmonic Gradient method (Refs 3 and 4). The TPS method is an extension of the IPS method by incorporating some three-dimensional (3-D) aspects in its formulation. The TPS method is a scalar approach because of its lack of coupling between the displacements acting along different axes, e.g., a displacements acting along the xaxis produces effect only along the x-axis. Therefore, it is not a truly 3-D method. By formulating the data transferal problem as an equivalent solid mechanics problem, Chen and Jadic (Ref 5) developed a boundary element method (BEM), called the BEM Solver, that generates a universal spline matrix S such that: