The knowledge of unsteady aerodynamic loads acting on an aircraft structure, which is moving either uniformly (steady) or accelerated (manoeuvring
Research and Modelling
Main topic is the reliable computation of unsteady aerodynamics, especially of phase shifts between harmonic structural oscillations and corresponding pressure fluctuations, for flutter prediction. Further topics are investigations of unsteady flow separation (buffet), of influences from gusts and vortices on lifting surfaces, impact of laminar-turbulent transition on aeroelasticity, as well as vortex separation on bluff bodies. These topics are mainly treated by RANS and Detached Eddy Simulations (DES).
Code validation regarding accuracy and regions of applicability of different unsteady aerodynamic CFD and fast methods is performed both by code to code comparison and by comparison with windtunnel test results. A special focus is put on unsteady flow separation, shock-boundary layer interaction, laminar flow as well as on control surfaces, wing-tail and wing-nacelle interferences. These topics are an essential part of the DLR projects HighPerFlex and iGREEN.
Different unsteady aerodynamic simulation tools are applied, according to the different problems of aircraft research and development to be solved, first of all the TAU code of DLR, but in addition also faster tools, which are developed especially for unsteady applications both in time and frequency domain, at DLR Institute of Aeroelasticity. Examples are Euler boundary-layer coupling in time domain, and in the frequency domain TDLM and iSKEM, both extensions of the Doublet-Lattice Method (DLM), as well as the linearised TAU code (in cooperation with DLR institute AS). The frequency domain methods need one or two steady flow field results as input for treating the superimposed unsteady flow. In addition Reduced Order Methods (ROM) are developed, which are for example based on a small number of TAU-RANS simulations, thus providing a data set which can be used to reconstruct a manifold of possible solutions for a wide range of frequency, kind of motion and Mach number. All fast and reduced methods are designed with compatibility to commercial software systems like NASTRAN and ZAERO.
Generation of aerodynamic data sets
Unsteady airloads induced by oscillatory motions based on TDLM, Euler boundary-layer coupling, as well as by the reduced order RANS method CFD4Flutter have been generated and have supported NASTRAN and ZAERO flutter computations, flight mechanic modelling of complete aircraft, as well as design of windtunnel models. Among others this work has been carried out within the EC projects MOB and AWIATOR, within national research project MODYAS and for the research aircraft HALO.