A Method for Deriving an Aeroelastic Model from Harmonic CFD Results

A Method for Deriving an Aeroelastic Model from Harmonic CFD Results

Abstract

Integrated dynamic models are derived for the aerodynamic part of the aeroelastic system. These are combined with a low order model describing the mechanical system to form a complete aeroelastic model. An aeroelastic wing flutter test is used for the validation of numerical procedures, and to validate the approach to calculate the flutter limit. Predictions of aeroelastic mode shapes are shown for increasing Mach numbers passing the flutter boundary. Parametric sensitivity studies are performed in order to understand error sources relating to experimental and numerical uncertainties. The method is general in terms of mode shapes, but here shown on 2 degrees of freedom modal description of the aeroelastic system. The structure, is described in terms of mass, spring stiffness and damping. The aerodynamic modal properties are obtained as 2:nd order expansions in frequency of the blade forces projected on to the different modes. The frequency-blade force relation is obtained numerically with the help of 3D, linear CFD calculations of the wing. The computations are performed mode by mode with a prescribed wing motion for a range of vibration frequencies. The pressure response on the wing surface defines then the aerodynamic blade force, resulting from the motion. The paper includes validation of the linear harmonic Euler CFD method, and the derivation and validation of the aeroelastic model.

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