Ein modulares Verfahren für die numerische aeroelastische Analyse von Luftfahrzeugen

• A modular method for the numerical aeroelastic analysis of air vehicles

Braun, Carsten; Ballmann, Josef (Thesis advisor)

Aachen : Publikationsserver der RWTH Aachen University (2008)
Dissertation / PhD Thesis

Aachen, Techn. Hochsch., Diss., 2007

Abstract

In order to assure economic efficiency and operational safety of new aircrafts, it is necessary to accurately consider the interaction of the elastic aircraft structure and the airflow in early stages of design. For a reliable prediction of effects arising from the interaction of the fluid and the structure the simultaneous solution of the governing equations for both domains is essential. Since flight speeds close to the speed of sound lead to significant flow-induced non-linear effects it is necessary to apply the Navier-Stokes equations in order to model the compressible, viscous fluid flow. The computational method SOFIA (Solid-Fluid-Interaction) solves the system of aeroelastic equations in the time-domain under consideration of flow induced non-linearities and facilitates the analysis of static and dynamic aeroelastic effects especially in the transonic flow regime. The core of SOFIA is the Aeroelastic Coupling Module (ACM), which has been developed and applied in the framework of the present dissertation. The ACM allows for a modularized assembly of SOFIA from different Euler- or Navier-Stokes-based flow solvers and FE-based structural solvers. Generalized program interfaces ensure the exchangeability of the codes for the different fields. The coupling module ACM coordinates the sequence of solver calls for static and dynamic aeroelastic computations in the sense of a partitioned procedure. Different improved "loose" strategies with prediction-/correction-steps and strong coupling strategies are provided. These strategies are aiming for a minimization of numerical errors resulting from inadequate energy transfer which is often inherent in basic loose coupling strategies. The improved staggered strategies allow for a good compromise between numerical effort and accuracy and stability of the partitioned procedure and thus facilitate the application of SOFIA to realistic problems. The ACM provides a local node-based method to exchange loads and displacements between the discretized sub-domains even with non-matching interface meshes. This method fulfils the requirement to conserve mechanical energy as well as global forces and moments. The applied load/displacement transfer algorithm is capable of exchanging coupling information between the discretized fluid domain and a structural model, which optionally consists of beam, shell, or volume elements. The validation of SOFIA for steady and unsteady aeroelastic applications has been performed by comparison of numerical results with experimental data for a swept wing model in subsonic flow. A good agreement for all test cases in terms of global aerodynamic forces and moments, pressure distributions and model deformations was found. SOFIA has been applied in the framework of the project HiReTT (High Reynolds Number Tools and Techniques) to investigate the influence of wing deformations on the aerodynamic characteristics of wind tunnel models in high Reynolds number experiments. The investigations revealed, that occurring wing deformations can significantly alter the flowfield and that experimental data can not be interpreted correctly without knowledge about the underlying model deformation. After extensive validation for subsonic and transonic aeroelastic problems, SOFIA has been used for the design and analysis of a wind tunnel model for transonic aero-structural dynamics experiments at realistic flight Reynolds numbers in a cryogenic wind tunnel. The main focus of SOFIA’s application was the assessment of the steady and unsteady aeroelastic behaviour under systematic variation of angle of attack, Reynolds number, Mach number and wind tunnel pressure. The extensive set of data collected during the numerical investigations was used to optimize the test programme for the planned, cost-intensive wind tunnel experiments.