Numerical Investigation Of Aeroelastic Wing Behavior Using CFD/CSD

Aeroelastic design of the wings is one of the crucial contents of aircraft development and retrofit. The transonic flight region presents the most serious conditions for aeroelastic instability since the wing experiences a sharp drop of the flutter behavior (transonic dip). The large deflection normally induces obvious changes in the characteristics of original wing structure and turns into an important aspect in the occurrence of limit-cycle oscillation (LCO). Some nonlinear factors, such as transonic flow and large deflection, are usually involved in the wing aeroelasticity, and make the associated computational analyses and physical mechanism be more complicated. Therefore, numerical investigation on nonlinear aeroelasticity currently becomes the theoretic hotspot and research challenge in international community. Another leading subject in aeroelasticity, which could significantly improve the efficiency of aerodynamic analysis in the transonic region, occurs to meet the demand of engineering design. This dissertation sticks to research progresses as highlighted above and performs relevant explorations and applications that will include:high precision aeroelastic analysis and interface interpolating approaches, reduced order model for the aerodynamics and its utilization in efficient flutter prediction, and aeroelastic mechanism studies of two typical wings.A nonlinear aeroelastic analysis approach using computational fluid dynamics/computational structure dynamics (CFD/CSD) is developed and applied to the study of transonic LCO that involves large structural deflection,(â…°) A quadrilateral flat-shell element is established, and it consists of a plate part for thick/thin plate analysis and a membrane part with high performance. Based on updated Lagrange (UL) scheme, geometrically nonlinear formulation is derived for the modeling of the structure with large deflation, large rotation and small strain. Newmark integration method is used for the time advancing of structural dynamics.(â…±) A new type interface interpolating method with the character of local form is presented and applied to fluid-structure interaction (FSI) problem. Thin plate spline is selected to fitting the function for displacement interpolation, and relevant domain is set effectively in a local form. Aerodynamic interpolating matrix is derived according to the energy conservation principle.(â…²) The transonic flow is governed by the Euler equations. A cell-centred finite volume approximation, in conjunction with the implicit dual time-stepping scheme, is used to discretize the governing equations. Also CFD calculation is conducted by parallel computing. The modules of nonlinear structure analysis and interface interpolation present as the subroutine of CFD solver, thus producing a FSI analysis capability. The transonic flutter simulation indicates the validity of presented CFD/CSD approach. Meanwhile, large-amplitude LCO of a cropped delta wing is studied, and its analysis precision is obviously better than existing results.An ARMA-based reduce order model (ROM) of unsteady aerodynamics is developed on the basis of CFD technique and system identification theory. The aerodynamic ROM is applied to efficient numerical study on transonic flutter problem. As a key aspect of ROM, the training procedure that involves generalized "3211" type input is formally conducted by the use of CFD/CSD. Then system identification toolbox in MATLAB environment is used for the estimation of system parameters and the verification of built model. The coupling of aerodynamic ROM and structural modal superposition method constitutes the flutter and servo-flutter analysis capability. Transonic flutter simulations of NACA0012airfoil and AGARD445.6wing indicate the precision and efficiency of the proposed ARMA/ROM. Besides, servo-flutter analysis of BACT airfoil in the transonic region is conducted by the ROM method, and the results indicate that active deflection of control surface heightens the flutter speed efficiently.Numerical investigations of transonic flutter and LCO behavior of new transport-type wing and cropped delta wing models are performed based on the general purpose FSI solver. Flutter characteristics of the basic transport wing numerically approach to the existing experimental values, and relevant LCO phenomenon is caused by the large-amplitude shock-wave motion. Contrastive analyses indicate that the winglet and C-type wingtip produce remarkable adverse effects on flutter characteristics of transport wing. Also the aerodynamic and mass effects of wingtip devices are identified separately by way of setting virtual mass. The simulation of the LCO of cropped delta wing correlates well with the experimental measurement. For lower dynamic pressures, geometric nonlinearity provides the proper mechanism for the development of the LCO. For higher dynamic pressures, material nonlinearity that arises from plasticity leads to a rapid rise in the LCO amplitude. This study demonstrates that material nonlinearity could have a remarkable influence on the aeroelastic behavior in some specific situations.Finally, the accomplished work of this dissertation is summarized, and the prospect of further research is also discussed.