Martin Siggel

System Studies on Active Thermal Protection of a Hypersonic Suborbital Passenger Transport Vehicle

Aerodynamic heating is a critical design aspect for the development of reusable hypersonic transport and reentry vehicles. The reliability in terms of thermal resistance is one of the major driving factors with respect to the design margins, the mass balance and finally the total costs of a configuration. Potential designs of active cooling systems for critical regions such as the vehicle nose and leading edges are presented as well as preliminary approaches for their impact on the total mass. The visionary suborbital passenger transport concept SpaceLiner is taken as a reference vehicle for these studies. Covering the whole flight regime from subsonic to Mach numbers of more than 20, this vehicle creates high demands on the thermal protection system. Part of the work was performed within the DLR research project THERMAS.

An Integrated Method for Propulsion System Conceptual Design

The conceptual design of future, potentially highly integrated aircraft engines pose a variety of new design options to the propulsion system engineers. In order to find the best conceptual design, rapid evaluation of many design choices is essential. However, traditional, fast evaluation methods employing historical and empirical data can only be applied to novel engine concepts to a very limited degree. Thus, swift conceptual design methods based on physical approaches providing a sophisticated level of detail are needed. The current paper presents a methodology focused on conceptual engine design. The methodology is based on the gas turbine simulation framework GTlab, which integrates software tools for engine performance, component aerodynamics and structural design. For conceptual design a dedicated set of design tools exists — the so called GTlab-Sketchpad. Sketchpad tools have full access to the thermodynamic design data of the engine performance module. Based on cycle analysis, the tool set generates parametric representations of the propulsion system components and stores the results back to the frameworks data model. Computational time is limited to a few seconds, to ensure interactivity during the design process. The graphical user interface provides means to interactively modify the design parameters and to immediately evaluate their impact on the overall design. Since the internal data model facilitates three dimensional parameterizations of the engine components, 3D representations of the engine designs can be generated by interfacing an open source CAD-kernel. For the present paper, the conceptual design process of a commercial jet engine utilizing GTlab-Sketchpad is shown. The underlying computational methods are described and the resulting 3D-geometry is presented.Copyright

Reproducing Existing Nacelle Geometries With the Free-Form Deformation Parametrization

In the conceptual and preliminary aircraft design phase the Free-Form Deformation (FFD) is one of various parametrization schemes to define the geometry of an engines nacelle. In this paper we present a method that is able to create a G2 continuous approximation of existing reference nacelles with the B-spline based FFD, which is a generalization of the classical FFD. The basic principle of our method is to start with a rotational symmetric B-spline approximation of the reference nacelle, which is subsequently deformed with a FFD grid that is placed around the initial geometry. We derive a method that computes the displacement of the FFD grid points, such that the deformed nacelle approximates the reference nacelle with minimal deviations. As this turns out to be a linear inverse problem, it can be solved with a linear least squares fit. To avoid overfitting effects - like degenerative FFD grids which imply excessive local deformations - we regularize the inverse problem with the Tikhonov approach. For the reference geometries we selected the NASA CRM model and the IAE V2500 engine. Both resemble nacelles that are typically found on common aircraft models and both deviate sufficiently from the rotational symmetry. We demonstrate that the mean error of our approximation decreases with an increase of the number of FFD grid points and how the regularization affects these results. Finally, we compare the B-spline based FFD with the classical Bernstein based FFD for both models.