CAD in Aerodynamic Aircraft Design

Computational fluid dynamics (CFD) has become a state of the art analysis tool for nearly all phases of aircraft design. In contrast to CFD, computer aided design (CAD) is traditionally used in later design phases of an aircraft, when the design is almost frozen. However, with the appearance of parametric CAD systems a new design methodology was enabled, which was based on the capability of a parametric CAD system to replay construction sequences with varied design parameters. A parametric wing can be re-used to create a vertical tail plane or parts can be associated to other parts, which allow concurrent engineering practices. In the present study, these capabilities have been exploited to generate extremely variable aircraft CAD models ready for CFD. Furthermore, parametric construction strategies, which have been developed in the past, are applied to model the primary aircraft parts, such as wing, fuselage and nacelle and also secondary parts, such as the belly fairing, wing tips and pylon, with the CAD system CATIA V5. For the construction of curves, which are used to create surface lofts, primarily B-splines are utilized, where the coordinates of the control points can later be used as the design parameters. Finally, the capabilities of parametric CAD are demonstrated through design variations performed for conventional configurations and through design studies with non-conventional aircraft configurations, which are in the focus of current research

Lagrangian Particle Tracking on Large Unstructured Three-Dimensional Meshes

A prerequisite for the prediction of ice accretion on an aircraft flying through clouds of supercooled liquid water is the accurate determination of the water impingement rate on various components of the aircraft. For this purpose, a droplet impingement module has been developed using the datastructure of the unstructured Navier-Stokes solver TAU. Since nowadays large computational grids are common practice, an efficient algorithm for determination of the droplet trajectories on such grids had to be implemented. This paper describes the physics and details of the implemented numerical algorithm. It summarizes lessons learned during development. The paper concludes with the presentation of code validation results and examples of applications

Comparison between Gradient-free and Adjoint Based Aerodynamic Optimization of a Flying Wing Transport Aircraft in the Preliminary Design.

This paper describes investigations of planform and shape optimizations for a flying wing transport aircraft with an Euler continuous adjoint method. For a prescribed lift the cost function will be the drag, which has to be minimized and implies a maximization of L/D. The results presented for the gradient based method using an adjoint solver are compared to an optimization performed with a gradient free approach. The different workflows and procedures will demonstrate the advantages and disadvantages of each particular optimization approach. The optimization procedure uses a freeform deformation technique for the design parameterization of the shape as well as for the surface mesh deformation required to determine the gradients. This combination of both tasks into one tool is advantageous because performing finite differences for evaluating the mesh sensitivities can be carried out with a constant grid topology. An example design case is also shown for demonstration purposes

Investigation and Minimization of Upsweep Drag of Aft-Loading Military Transporters with Tail Strakes

The use of tail strakes on aft loading transport aircraft is a well proven technique to reduce fuselage upsweep drag. In the present paper the tail flow around a generic aircraft configuration with a swept up tail has been computed using high fidelity CFD analyses. The focus was on the influence and effectiveness of tail strakes and the interaction of the strake with the tail vortices. As it turned out that strakes placed arbitrarily may lead to decrease of aircraft performance, CFD based optimization runs were conducted to find an optimal strake position on the rear fuselage. Finally the optimized configurations were analyzed and the principle of strake tail vortex interaction aiming on a reduction of upsweep drag was clarified

Prospects of Geometry Parameterization based on Freeform Deformation in MDO

In MDO, related to aircraft design, geometry parameterization has been identified to play a key role. In the present approach the freeform deformation technique has been adopted, which requires a preparation of adequate lattices to achieve a desired variation of a given geometry. For the generation of those lattices the DLR grid generation system MegaCads is utilized. Practicability and prospects of the present method are demonstrated for typical optimization problems in aerodynamic shape design

Aircraft Geometry Parameterization with High-End CAD-Software for Design Optimization.

The present paper focuses on the possibilities and strategies to model parametric and aircraft shapes with a high-end CAD system in the context of design optimization. As an example the modeling of a propeller with crescent-shaped blades is described. Additionally the problem of airfoil parameterization within a CAD system is also touched. The use of pa-rametric associative modeling starting from design tables and ending with CFD-ready ge-ometries is demonstrated for a wing body configuration. Finally, a novel method is introduced to support CFD volume mesh deformation with auxiliary structured surface grids. This will enable the use of parametric CAD in combination with the adjoint approach, what is still in open issue in design optimization

Numerical Shape Optimization

Numerical Shape Optimizatio