Arno Ronzheimer

Development and application of multi-disciplinary optimization capabilities based on high-fidelity methods

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.

Aircraft Wing Optimization Using High Fidelity Closely Coupled CFD and CSM Methods

The present paper describes a comprehensive MDO process chain to maximize the range of a transonic transport aircraft configuration. The parameterization incorporates wing plan form parameters and twist angles in four wing sections. The geometrical inputs for the disciplines CFD and CSM were generated by CATIA V5 based on those design parameters which were prescribed by a SUBPLEX optimizer. CFD is at first used to calculate the drag in cruise flight with RANS and secondly to provide aerodynamic forces from Euler solutions from certain maneuver cases for a structural sizing of the wing to yield the wing weight. As with the structural calculations the wing deformations are available, these are used to deform the CFD mesh and to evaluate drag and forces on the corresponding flight shapes. The fluid/structural-sizing procedure, which is performed in every optimization cycle, is repeated several times until a sufficient convergence of drag and wing mass is achieved. Both values are then used to compute the Breguet range, which represents the optimization objective. Finally two optimization runs have been conducted. While the first run lead to a consistent result, in the second run, which includes an additional load case, the best configuration was already found in the fifth cycle.

Computation of Aerodynamic Coefficients for the DLR-F6 Configuration using MEGAFLOW

Navier-Stokes calculations, obtained with software from the MEGAFLOW project, are presented for the Airbus-like DLR-F6 configuration at cruise flight conditions. Results for the wing-fuselage geometry are available for structured grids of different sizes up to 16 million grid cells. The Baldwin-Lomax turbulence model is used and the influence of the numerical dissipation is analyzed. It is demonstrated that even 16 million grid cells are not sufficient to reach a fully grid converged solution for this configuration at transonic flow conditions, if standard non-adapted grids are used. The influence of the numerical dissipation on the pressure distribution is very small for the fine grid. However, the drag coefficient shows a variation of 2.5% for different levels of numerical dissipation. For the configuration with pylon and nacelle, grids with 3.3 and 3.8 million cells are used. In addition to the Baldwin-Lomax model, first computations using the k-ω turbulence model from Wilcox are presented. The pressure distributions as well as the lift and drag coefficients are compared to wind tunnel measurements for both configurations. The comparison shows a good quality of the numerical results.

Aerodynamic Optimal Engine Integration for a Business Jet Configuration.

For a generic transport aircraft configuration with engines installed at the tail optimizations were performed with design parameters deforming the shape of fuselage tail, pylon and nacelle successively to assess the potential of each component. To perform the simulation based optimizations in an adequate time frame the Euler equations have been solved since comparisons with viscous flow calculations showed that transonic effects which were responsible for installation interference effects were predicted reasonably well. Finally the viscous drag of all optimized geometries, promising drag savings of nearly 5 drag counts from the inviscid calculations, were re-calculated solving the Reynolds-averaged Navier-Stokes (RANS) equations. While these final assessments also demonstrated drag savings, the predicted gain is smaller, which leads to

High Lift Design and Aerodynamic Assessment for an Over-the-Wing Pylon-Mounted Engines Configuration with STOL Capabilities

A CFD-based assessment of the low speed high lift performance of an over-the-wing mounted engine installations for a short range airliner with STOL capabilities is presented in this paper. The configuration is representative for a 100 passenger aircraft and characterized by pylon mounted over-the-wing installed UHBR-engines. The high lift system features active segmented and highly deflected Coanda flaps and a specifically designed droop nose at the leading edge of the wing. The study is part of the Collaborative Research Center 880 that develops technologies and configurations with quite STOL capabilities. The layout of the high lift system is described, together with the numerical approach and results for the considered test case. The objective of the present study is to investigate a short chord active plain flap in landing configuration and assess the maximum lift capabilities against target values from preliminary design studies of the CRC 880. It is a first step towards a more comprehensive assessment of variants of the high lift system. With the typical lift generation for a circulation control supported high lift system, the analysis of the stall behavior reveals a favorable smooth lift breakdown starting at the inner wing. Yet, the maximum lift properties fall short of the target value, so that an enlarged chord flap will be considered as a next step to comply with the maximum lift requirements.

Aerodynamic Optimal Engine Integration at the Fuselage Tail of a Generic Business Jet Configuration

Aerodynamic interference effects of jet engines installed at the tail of a generic business configuration are investigated using numerical flow simulations based on the solution of Euler equations. It is demonstrated that the channel contour formed by fuselage tail, pylon and nacelle dominates the flow behavior and also the resulting interference drag. A simulation based optimization process chain is then used to minimize the interference drag in cruise flight by applying the freeform deformation method for re-shaping of the fuselage tail.