ENGINEERING AND CFD

In order to significantly reduce the drag and the environmental impact of future aircraft, considerable effort has to be undertaken in all fields of aircraft design. Besides reducing drag around the cruise condition of typical transport aircraft, it is also of great interest to expand the flight envelope in order to allow for a more flexible design. Understanding the behaviour of a commercial transport aircraft at the limits of its flight envelope, away from its design point, requires either expensive flight testing, tests in sophisticated wind tunnel facilities or advanced computational models. As flight tests are very expensive and take place in a late phase during the development of a new aircraft, when most of the design is already fixed, virtual flight tests, which can be performed iteratively during the design process, would be a preferred alternative.

In order to significantly reduce the drag and the environmental impact of future aircraft, considerable effort has to be undertaken in all different fields of aircraft design. In this context, aerodynamics play an important role. Besides reducing drag around the cruise design point of typical transport aircraft, it is also of great interest to expand the flight envelope in order to allow for a more flexible design. Such studies were carried out as part of the European-Russian project BUTERFLI, where the effect of local contour modifications (so called “Shock Control Bumps”) of the wing on drag and the limits of the flight envelope were analysed.

Understanding the behaviour of a commercial transport aircraft at the limits of its flight envelope, away from its design point, requires either expensive flight testing, tests in sophisticated wind tunnel facilities or advanced computational models. Conditions such as subsonic stall or transonic buffet are characterized by unsteady separated wakes (see Fig. 2) and require accurate and efficient computational methods. The DFG project “Studies on the Development of Massively Separated Wakes of Aircraft” focused on these topics, leveraging measurement data accumulated during the European project ESWIRP.

As flight tests are very expensive and take place in a late phase during the development of a new aircraft, when most of the design is already fixed, virtual flight tests, which can be performed iteratively during the design process, would be a preferred alternative. The project VitAM (Virtual Aircraft Model) aims to contribute in a development process of virtual flight tests.

Computational fluid dynamics represents a powerful method to address all those problems of aerodynamic aircraft design – but also comes with high computational costs. Hence, the project SCBOPT (Shock Control Bump Optimization) combines the computational part of all those efforts at HLRS, using the CRAY XC40 Hazel Hen for multiple flow simulations with DLR-TAU and DLR-FLOWer flow solvers.

The studies carried out within the SCBOPT project enhanced the understanding of flow control for drag reduction and produced valuable results from which further insight in relevant flow phenomena close to the boundary of the flight envelope has been obtained. Those results will help to further develop numerical methods for such challenging flow conditions and will significantly increase their reliability.

Project Team:

Thorsten Lutz (PI), Rouven Mayer, Jens Müller, Junaid Ullah, Andreas Waldmann
Aircraft Aerodynamics Group, Institute of Aerodynamics and Gas Dynamics, University of Stuttgart

References:

[1] Lutz, T., Gansel, P.P., Waldmann, A., Zimmermann, D.M., Schulte am Hülse, S.: Prediction and Measurement of the Common Research Model Wake at Stall Conditions. Journal of Aircraft 53(2), 501-514 (2016). DOI 10.2514/1.C033351.

[2] R. Mayer, D. Zimmermann, K. Wawrzinek, T. Lutz, and E. Krämer. Numerical Study of Three-Dimensional Shock Control Bump Flank Effects on Buffet Behavior. High Performance Computing in Science and Engineering ‘15, 2015.

[3] Waldmann, A., Gansel, P.P., Lutz, T., Krämer, E.: Unsteady Wake of the NASA Common Research Model in Low-Speed Stall. Journal of Aircraft (to be published) DOI 10.2514/1.C033413.

[4] Zimmermann, D.-M., Waldmann, A., Lutz, T., Krämer, E.: Development of Flow Structures in the Near-Field Wake Region of the Common Research Model. 5th CEAS Air & Space Conference, Delft, Netherlands (2015).

Scientific Contact:

Dr.Thorsten Lutz
Gruppenleiter Luftfahrzeugaerodynamik / Gruppenleiter Windenergie
Institut für Aerodynamik und Gasdynamik, Universität Stuttgart
Pfaffenwaldring 21, D-70569 Stuttgart (Germany)
e-mail: lutz[at|iag.uni-stuttgart.de