Time marching analysis of flutter using computational fluid dynamics

Abstract

The maturity of simulation codes for aerodynamics (CFD) and structures (CSD) now leads to high fidelity computations of single discipline problems. The problem of aircraft flutter involves the coupling of aerodynamics and structures and has led to an interest in coupling CFD and CSD codes. There is strong motivation to couple existing codes to simulate this problem to avoid developing new methods since current single discipline methods are both well established and differ in their formulation (Eulerian fluids descriptions based on finite volume methods and Lagrangian finite element methods for structures). Recent work on the sequencing of codes has addressed the time sequencing issue which can be resolved by an iterative scheme to make sure that both simulations advance simultaneously in time. The regeneration of volume grids around a deforming geometry has also received attention.A third problem involves the passing of loads and displacement information between the fluid and structural surface grids. These grids will not in general coincide and it is likely that they will not even lie on the same surface. This thesis considers this problem and evaluates several existing and proposed solutions from the point of view of geometrical considerations and time marching flutter analysis. The test cases considered are for the AGARD 445.6 wing and the MDO wing. A boundary element formulation is also considered both for the elimination of the transfer problem and also a transformation method.A successful evaluation of the influence of the transformation method on the time marching response of a wing in a transonic flow is given and is based on the decomposition of the transformation into two components inwards and outwards of the plane of the structural model's plane

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