No abstract

Numerical simulation is already an important cornerstone for aircraft design, although the application of highly accurate methods is mainly limited to the design point. To meet future technical, economic and social challenges in aviation, it is essential to simulate a real aircraft at an early stage, including all multidisciplinary interactions covering the entire flight envelope, and to have the ability to provide data with guaranteed accuracy required for development and certification. However, despite the considerable progress made there are still significant obstacles to be overcome in the development of numerical methods, physical modeling, and the integration of different aircraft disciplines for multidisciplinary analysis and optimization of realistic aircraft configurations. At DLR, these challenges are being addressed in the framework of the multidisciplinary project Digital-X (4/ 2012-12/2015). This paper provides an overview of the project objectives and presents first results on enhanced disciplinary methods in aerodynamics and structural analysis, the development of efficient reduced order methods for load analysis, the development of a multidisciplinary optimization process based on a multi-level/variable-fidelity approach, as well as the development and application of multidisciplinary methods for the analysis of maneuver loads.

No abstract

The numerical investigation of dynamic responses to atmospheric turbulence is an important task during the aircraft design and certification process. Efficient methods are desirable since large parameter spaces spanned by e.g. Mach number, flight altitude, load case and gust shape need to be covered. Aerodynamic non-linearities such as shocks and boundary layer separation should be included to account for transonic flight conditions. A linearised frequency-domain method is outlined to efficiently obtain gust responses using computational fluid dynamics. The Reynolds-averaged Navier-Stokes equations are linearised around a steady-state solution and solved for discrete frequencies. The resulting large but sparse system of linear equations can then be evaluated significantly faster than its time-domain counterpart. The method is verified analysing sinusoidal gust responses for an aerofoil and a large civil aircraft considering a broad range of reduced frequencies. Derivatives of aerodynamic coefficients and complex-valued surface pressures are compared for time-and frequency-domain approaches. Next, 1-cos gusts are investigated using an incomplete inverse Fourier transform in conjunction with a complex-valued weighting function to discuss time histories of lift coefficients as well as surface pressures. Finally, introduced techniques are applied to conditions arising from certification requirements to demonstrate the technical readiness. The methods discussed present an important step to establish computational fluid dynamics in the routine aircraft loads process.

Each perturbation of an aircraft state in trim induces aerodynamic loads on wings, control surfaces and other parts of an aircraft. These loads have to be quantified for a wide range of flight states covering the flight envelope. Small disturbance approaches based on the Reynolds-averaged Navier Stokes equations fulfil the requirements of efficiently predicting accurate dynamic response data. These time-linearized methods have been successfully applied in flight dynamic and aeroelastic analyses for moderate flight conditions. Small disturbance approaches on the basis of Navier-Stokes solvers have become most often the right choice, for example in flight dynamic and aeroelastic analysis, to combine efficiency and accuracy for predicting dynamic response data. However, in complex flows exhibiting shock-induced separations, deficits in robustness of the iterative solution methods often lead to simplifications of the equations and thus reducing the quality of the computed results. The presented linearized frequency domain solver has shown accurate results compared to nonlinear time-accurate unsteady simulations for attached flow conditions. The area of application is extended to separated transonic flows demonstrating the method's capability to accurately capture strong shock-boundary interactions. Deriving the exact linearization of the turbulence model as well as implementing a robust method to solve the stiff linear systems are key tasks to achieve this target. Results are presented for the LANN wing undergoing rigid body motions comparing dynamic derivatives of lift and moment coefficients between the linearized frequency domain solver and its time-domain counterpart. In addition, local surface pressure and skin friction coefficients are analysed at two span stations. The presented linearized frequency domain solver (TAU-LFD) has shown accurate results in comparison to fully time-accurate unsteady simulations at separated transonic flow conditions.