Martin Kruse’s research while affiliated with German Aerospace Center (DLR) and other places

Results for the numerical aerodynamic design and analysis of a long-range, large passenger aircraft equipped with a Hybrid Laminar Flow Control (HLFC) system are presented. This work was performed within the European project HLFC-WIN. The reference geometry of this study is the long-range cruise Airbus research XRF1 geometry, designed for turbulent flow. The HLFC part of the wing is restricted to an outer wing region which extends from the engine mounting to the wing tip. To achieve laminar flow in the outer wing, nose suction panels are used and the wing shape is changed. The aerodynamic HLFC wing design is performed at different cruise flight conditions. It involves shape design and optimization of the suction distribution. The shape design was performed using the DLR 3D transonic inverse design code. Results for the shape design are presented for three geometries. The first one is a DLR redesign of an HLFC variant of the XRF1 aircraft designed by Airbus. This geometry is used for the HLFC-WIN ground base demonstrator. Design was performed at the cruise design point and for off-design conditions. This design presents two improvements in comparison to the initial geometry: a) an increased laminar extent for the cruise design point and b) an increased spanwise thickness distribution, which leads to a thickness distribution comparable to the reference geometry. A second HLFC design was performed which improved the cruise design point aerodynamic performance of the first design, also by reducing wave drag. In a third design it was shown that in the region of the outermost suction panel a natural laminar flow (NLF) design was possible by using for the nose a crossflow attenuated NLF (CATNLF) strategy. The shape design was performed on simplified geometries. For final shape designs complete configuration CFD solutions were obtained using the TAU RANS solver of DLR. The aerodynamic performance of the different HLFC geometries was assessed by using the ffd72 far-field drag analysis software of ONERA for these solutions. In the shape design a generalized suction distribution based on the suction distribution of the Airbus HLFC design was used. After the shape design, the suction distribution was optimized for the GBD-DLR-2 design in order to minimize the suction power. A novel combined approach of variable porosity outer skin and suction chambers was introduced. In addition to the design and analysis of the HLFC geometries this work also describes extensions of the numerical methods used to predict the transition line position in the case of boundary layer suction. The physical representation of surface suction was improved by implementing and testing a direct suction boundary in the TAU solver

This paper presents the aerodynamic performance analysis of realistic large passenger aircraft equipped with a Hybrid Laminar Flow Control (HLFC) system. To this purpose, the design of two HLFC aircraft geometries is first outlined, both designed by DLR based on an Airbus HLFC variant of the XRF-1 geometry. Numerical simulations were performed with the TAU RANS solver of DLR, using an extension of its LST-based automatic transition prediction capability for cases with boundary layer suction. Aerodynamic performance assessment was then performed using the ONERA ffd72 far-field drag analysis software, allowing comparisons between configurations in terms of phenomenological drag components. The overall assessment of the different configurations considers both the laminarization benefit using HLFC technology compared to a fully turbulent reference aircraft and the performance penalty when the HLFC wing is operated under fully turbulent conditions. Results of the analysis are consistent with the geometry modifications and the flow physics, highlighting an overall HLFC benefit via the reduction of friction and viscous pressure drag components. A wave drag penalty, inherent to the laminarization of the outer wing upper surface, is identified in the original HLFC geometry designed by DLR and reduced in its further improved version.

DLR has developed a distributed collaborative MDO environment. A multi-level approach combining highly-fidelity MDA for aerodynamics and structures with conceptual aircraft design methods is employed. Configuration-specific critical loads are used for sizing the structure. It is used to optimize the fuel burn of a long-range wide-body transonic transport aircraft configuration. The focus of this talk is on how the MDO was implemented based on DLR standards and tools and the setup of the optimization problem.

Based on a fully designed wing box section of a generic transport aircraft, two effects are investigated leading to surface waviness, namely process induced deformations (PID) and load induced deformations (LID). A DLR in-house waviness handling tool for the analysis and superposition of multiple waviness effects is introduced and applied. It is shown, that the results differ widely whether or not the effects are evaluated together. Finally, the remaining waviness is aerodynamically analysed using established methods.

In the usual approach to multi-disciplinary optimization (MDO), a few experts in optimization select and integrate disciplinary tools into a working MDO process, run it on target cases, and analyze the results. This approach is expedient, but it tends to oversimplify employment of disciplines. German Aerospace Center (DLR) is currently pursuing a more cooperative approach, where disciplinary experts from different DLR institutes are involved throughout in the definition, implementation, and evaluation of MDO processes. The goal is to establish a modular MDO platform, with well-balanced fidelity levels of employed disciplines, that can be used both for overall aircraft design, as well as for studying the influence of particular subsystem improvements on the overall design objective. Two MDO processes resulting from this effort so far are presented. The objective in both process is to minimize the mission fuel burn, as evaluated through Breguet range equation. One is a derivative-free process employing multi-level analysis, comprising the conceptual design level for determining the dependent top-level parameters, dynamic level for computing the sizing loads, and detailed level for sizing the structure and computing the performance indicators. The other is a gradient-based process on the detailed level alone, employing a split of design parameters between CAD-based and CAD-free, and treating all structural constraints independently. The set of sizing-relevant load cases is automatically determined based either on the actual configuration (in the derivative-free process) or on the baseline configuration (in the gradient-based process), rather than applying a set of generic load cases. The contribution concludes with several example studies carried out using these processes.

Thisreportpresents a multi-disciplinary optimization (MDO) processthatminimizes the mission fuel burn of an aeroelastic long-rangetransport aircraft configuration, by modifying the wing planform, twist, and structural element thicknesses. Two optimizations are performed, one where the fuel burn is approximately evaluated through Breguet range equation, and the other where the ordinary differential equation (ODE) for the step-climb cruise is formally integrated. This is done in order to determine if the Breguet equation is still sufficient in face of high-fidelity aeroelastic simulations. The two optimized designs ended up having similar improvements, thus confirming the applicability of the Breguet equation, for the number of design parameters that were employed.