An assessment of inter-grid transformation for a whole aircraft

As modern military aircraft become lighter, faster and more maneuverable, the consideration of aeroelastic effects during the design process can provide significant benefits. Computational aeroelasticity provides an attractive alternative to wind tunnel testing of flexible models in terms of accurately predicting and simulating the various linear and non-linear phenomena in a cost effective way. Computational Structural Dynamic (CSD) and Computational Fluid Dynamic (CFD) codes have reached a level of development where they can accurately analyse the structural and fluid behaviour. Aeroelastic simulation of individual components of an aircraft is now commonly done but problems arise when simulating a whole aircraft configuration. This is because the CSD solver calculates the elastic response' of the aircraft on a structural grid which usually does not coincide with the CFD surface grid and hence a scheme is required to transfer displacement and force values between the CSD and CFD grids. The various aerodynamic surface patches are driven by different structural components which may require different transformation methods. For example a fuselage, if modelled as a 1-dimensional beam, would require a different transformation technique than the wings which are modelled as 2-dimensional plates. To address this, a modified version of the Constant Volume Tetrahedron (CVT) transformation scheme is proposed for 1-dimensional structural grids. A tagging procedure is used where the fluid grid nodes are identified as being driven by 1 or 2-dimensional structural components and then the appropriate version of the transformation scheme is applied. The other difficulty is that the component interfaces in the fluid grid need to match up properly for the simulation to be successful. To overcome this a weighting method has been developed which forces the grid points at the component interfaces of the fluid grid to match up correctly by averaging the transformation within a predefined hierarchy. In the current work, this methodology has been demonstrated on a generic F16 aircraft configuration. The robustness of the transformation technique is evaluated by using a number of structural models to drive the fluid surface motions

Aeroelastic analysis of aircraft with control surfaces using CFD

For the simulation of control surface buzz accurate prediction of the shock location and the chock strength is essential and this is currently achieved using Euler and RANS based CFD analysis. To calculate the motion of the control surface only the flap rotation mode needs to be modelled. In the current work the CFD solver is coupled with a modal based FEM solver. The multi-level hierarchical blending transformation methodology is applied for the aeroelastic analyses of complex geometries. The methodology is used for the treatment of blended control surfaces and the effect of the blending on the aero-structural response is measured. Forced clap oscillations of a Supersonic Transport (SST) configuration are simulated and the dynamic deformation of the wing and the unsteady pressure due to the forced oscillations are validated against experiments. Transonic buzz on a trailing edge flap is investigated on the Supersonic Transport configuration using the RANS and the Euler equations. Characteristics associated with buzz instability are reproduced computationally and the effect of the flap on the wing flutter is measured. Finally, aeroelastic simulations are performed on the Hawk aircraft. The combat flap configuration of the Hawk aircraft is investigated using CFD and the effect of the flap on wing flutter is assessed. The aeroelastic response of the rudder at supersonic freestream Mach numbers is studied. The importance of aerodynamic interference on the aeroelastic behaviour is assessed

ANN BASED ROM FOR THE PREDICTION OF UNSTEADY AEROELASTIC INSTABILITIES

Abstract. A Reduced-Order Model (ROM) for the prediction of aeroelastic instabilities is presented. The unsteady nonlinear aerodynamic system is characterised by an Artificial Neural Network (ANN) to a set of network weights. The system is trained on a time history of simultaneous forced oscillation of the normal modes as input and generalised forces as output. Network weights are then used to approximate the aerodynamic force in the structural equation of motion to obtain the structural response. Results from the 3D Goland wing are presented and compared against full order CFD. It is shown that the ROM can predict aeroelastic instabilities with reasonable accuracy at a cost of less than one typical unsteady aeroelastic computation

Aeroelastic System Identification using Transonic CFD data for a 3D Wing

peer reviewedThis paper is part of a study investigating the prediction of aeroelastic behaviour subjected to non-linear aerodynamic forces. Of interest here is whether the sub-critical vibration behaviour of the aeroelastic model gives any information about the onset of the LCO. It would be useful to be able to use system identification methods to estimate aeroelastic models that characterise the LCO. Such a methodology would be very useful, not only for analysis with coupled CFD/FE models, but also during flight flutter testing. In this paper, the responses to initial inputs on the Goland Wing [9] CFD/FE model at different flight speeds are analysed to determine the extent of the non-linearity below the critical onset of LCO. Analysis is also performed using a linear identification model