Gust load analysis is a relevant part of the certification process of aircraft. In need of low computing times, industrial analysis procedures often rely mainly on low-fidelty numerical aerodynamics methods, such as the Doublet Lattice method (DLM). However, their accuracy with respect to loads has not been assessed sufficiently in comparison to high-fidelity methods in the past. In this paper, simulation results of a classical DLMbased gust load analysis process are compared to the results of an alternative process in which the DLM solver is replaced by the CFD solver TAU. The investigation is performed with a realistic modern passenger aircraft. It is studied how the consideration of different levels of multidisciplinarity in the simulations affects the overall loads. The simulation methodologies exploited in the CFD-based analysis process are outlined. It is shown that the gust load factors predicted with CFD are significantly lower than those of the classical DLM-based process-not only in the transonic flow regime, where benefits from the CFDbased analysis are expected, but also in the subsonic flow regime.
The expected computational power that will become available in the next years and decades will allow the introduction of more accurate simulations at earlier aircraft design stages. It is thus mandatory to identify and consequently develop multi-disciplinary optimization capabilities based on high-fidelity methods enabling the design of the future aircraft. The paper will give an overview of the latest development conducted at DLR in this field. Three representative applications will demonstrate benefits and limitations of the capabilities developed.
Nomenclature
FFD= Free-Form Deformation CD = Drag Coefficient CFD = Computational Fluid dynamics CL = Lift coefficient C SFC = Thrust Specific Fuel Consumption DC = Drag Counts (1DC=0.0001) HTP = Horizontal Tail Plane M = Cruise Mach Number MTOW = Maximum Take-Off Weight RANS = Reynolds Averaged Navier-Stokes Equations Re = Reynolds Number VTP = Vertical Tail Plane W = Weight
A new modal-based method that captures the geometric nonlinear effects that arise in the regime of large deformations of wing-like structures is presented. The most limiting factors of the modal approach are the linear force-displacement relationship and the representation of the nodal displacement field based on normal modes. The proposed extension includes stiffness terms that cubically depend on the generalized coordinates. The structural deformation is calculated not only by normal modes but also by higher order mode components that account for the foreshortening effect at beam-type structures. The approach is applied to a cantilever slender wing. Static and dynamic results are presented together with results from a commercial finite element solver and from the UM/NAST aeroelastic solver from the University of Michigan. The numerical study highlights the capability of the new approach to capture nonlinear effects while keeping the simplicity of the modal approach.
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