Abstract (Summary)
Because the flutter phenomenon of aircraft wings is usually associated with large deformations/deflections, the structural solution based on linear theory for the aircraft wings might give inaccurate or totally unphysical solutions. This is due to the equilibrium state of the structure is referred to the initial configuration, which can be very different with actual configuration at a given time when the wing deflection is large. So the changing geometry of the structure has to be taken into account in order to accurately describe the fluid/structure interactions at the onset of flutter, or in the post-flutter regime. The objective of the present study is to show the ability of solving fluid structural interaction problems more realistically by including the geometric nonlinearity of the structure so that the aeroelastic analysis can be extended into the onset of flutter, or in the post flutter regime. A nonlinear Finite Element Analysis software is developed based on second Piola-Kirchhoff stress and Green-Lagrange strain. The second Piola-Kirchhoff stress and Green-Lagrange strain is a pair of energetically conjugated tensors that can accommodate arbitrary large structural deformations and deflection, to study the flutter phenomenon. Since both of these tensors are objective tensors, i.e., the rigid-body motion has no contribution to their components, the movement of the body, including maneuvers and deformation, can be included. The nonlinear Finite Element Analysis software developed in this study is verified with ANSYS, NASTRAN, ABAQUS, and IDEAS for the linear static, nonlinear static, linear dynamic and nonlinear dynamic structural solutions. To solve the flow problems by Euler/Navier equations, the current nonlinear structural software is then embedded into ENSAERO, which is an aeroelastic analysis software package developed at NASA Ames Research Center. The coupling of the two software, both nonlinear in their own field, is achieved by domain decomposition method first purposed by Guru swamy. The improved diagonal form of Beam and Warming Scheme is used to solve the Euler/Navier Stokes equations. Total Lagrange Scheme is used for the structural solutions. The Newmark time integration scheme is used for the sub-iterations of the structural solutions within each time step to ensure the accuracy. The interaction of the structural dynamic and fluid flow is achieved by the fluid-structure interface, which also pre-exist in ENSAERO. For the accuracy of the flow field solutions, the algebraic adaptive moving grid is used to make the fluid flow boundary conform to the deforming wing geometry at every time step. Certain criteria are enforced to the adaptive grid scheme to make sure that the accuracy of the flow solutions is achieved. To the best knowledge of the author, it is the first time that a nonlinear Finite Element Analysis code is coupled with Euler and Navier Stokes equations directly. A procedure has been set for the aeroelastic analysis process. The aeroelastic analysis results have been obtained for fight wing in the transonic regime for various cases. The influence dynamic pressure on flutter has been checked for a range of Mach number. Even though the current analysis matches the general aeroelastic characteristic, the numerical value not match very well with previous studies and needs farther investigations. The flutter aeroelastic analysis results have also been plotted at several time points. The influences of the deforming wing geometry can be well seen in those plots. The movement of shock changes the aerodynamic load distribution on the wing. The effect of viscous on aeroelastic analysis is also discussed. Also compared are the flutter solutions with, or without i the structural nonlinearity. As can be seen, linear structural solution goes to infinite, which can not be true in reality. The nonlinear solution is more realistic and can be used to understand the fluid and structure interaction behavior, to control, or prevent disastrous events.
Bibliographical Information:


School:University of Cincinnati

School Location:USA - Ohio

Source Type:Master's Thesis

Keywords:aeroelasticity fea cfd fluid mechanics solid


Date of Publication:01/01/2003

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