Abdul Rampurawala

Aeroelastic Calculations for the Hawk Aircraft Using the Euler Equations

This paper demonstrates coupled time-domain computational-fluid-dynamics (CFD) and computationalstructural-dynamics simulations for flutter analysis of a real aircraft in the transonic regime. It is shown that a major consideration for a certain class of structural models is the transformation method, which is used to pass information between the fluid and structural grids. The aircraft used for the calculations is the BAE Systems Hawk. A structural model, which has been developed by BAE Systems for simplified linear flutter calculations, only has a requirement for O(10) degrees of freedom. There is a significant mismatch between this and the surface grid on which loads and deflections are defined in the CFD calculation. This paper extends the constant volume tetrahedron tranformation, previously demonstrated for wing-only aeroelastic calculations, to multicomponent, or full aircraft, cases and demonstrates this for the Hawk. A comparison is made with the predictions of a linear flutter code.

Evaluation of a Simplified Grid Treatment for Oscillating Trailing-Edge Control Surfaces

The aeroelastic behavior associated with control surfaces is of particular practical interest The treatment of the control surface in a computational fluid dynamics based simulation is complicated by the change in topology of the geometry as the flap edge is exposed. This paper evaluates the use of a treatment which blends the flap edge into the wing. This simplifies the mesh treatment by avoiding topological changes. The influence of the treatment of the forced flap motions on the aerodynamic responses of the rigid benchmark active control technology wing and a flexible supersonic transport wing is evaluated. Comparison is made with results obtained when the flap edge is exposed. It is shown that the predictions from the blended treatment give similar results, including local effects on the control surface, to calculations which include the flap edge effects.

Intergrid Transformation for Aircraft Aeroelastic Simulations

A transformation methodology is developed for complete aircraft aeroelastic computations. A Structural Dynamics Model based on a generic F16 aircraft has been used to study the intergrid transformation between the structural and fluid grids. A structural model with the fuselage modelled as 1D beam and the wings and the fin modelled as 2D shells is used to obtain the modal response. The Constant Volume Tetrahedron (CVT) is the transformation scheme used for communicating the deformation between the 2D structural components and the corresponding fluid surface components. A modified version of the CVT is used for the transformation between the 1D structural beam and the fuselage. A two level transformation scheme is applied and a hierarchical based blending function is applied at the component interfaces by which the fluid surface grid remains intact.

Treatment of Forced Flap Motions for Aeroelastic Simulations of an Arrow Wing

This study describes a CFD based simulation of an oscillating trailing edge control surface on a flexible arrow wing. The computed unsteady surface pressure distribution and the deformation of the wing due to the control surface oscillation are validated against experimental results. The structure of the wing is modelled so that the first wing bending mode resonates with the flap oscillating frequency (FOF) of 15 Hz as observed in the experiments. A predefined flap mode is applied to the surface grid to implement the forced flap oscillations. The FEM package NASTRAN is used to model the structure and the CFD code PMB developed at University of Glasgow is used for the simulations.

Treatment of Complex Configurations for Flutter Calculations

The transfer between fluid and structural grids in an aeroelastic simulation is considered. A method for blending the transformation of different aircraft components is described. This method is also used to blend control surfaces into the wing or fin. Evaluation of this treatment is made against results obtained when the flap has a small gap at its ends. The integrity of the method has been tested by the successful application to a practical example of rudder buzz.