Joint Research Project SaFuMa

Semi-active flutter suppression using aerodynamic measures

This joint research project is funded by the Federal Ministry for Economic Affairs and Energy as part of the Climate VII-1 aviation research program.

Project ID: 20E2409B
Project period: 1.10.2025 to 31.5.2028

Objectives of the joint project:

SaFuMa is a joint research project with the overall objective of investigating various passive methods with regard to their potential for flutter suppression on high-aspect-ratio wings and fan rotor blades and to better understand the underlying physical phenomena.

Passenger aircraft operate in the transonic regime. Although the cruise speed is well below the speed of sound, the acceleration of the airflow over the wing causes local areas of supersonic flow. To maximize aerodynamic efficiency, the wings of modern commercial aircraft have increasingly longer spans and aspect ratios. This reduces drag and thus fuel consumption, but the larger span of the wing also reduces its bending stiffness.The transonic flow, together with the increasingly flexible wings, can cause even a small disturbance (such as a gust of wind or an increase in airspeed) to trigger a critical condition known as flutter. The aerodynamic forces deform the wing in such a way that the flow changes. The changed flow in turn affects the air forces, which can result in a self-excited oscillating system. Reinforcing the wing structure counteracts this effect but also leads to a higher weight. The same effect can occur with the rotor blades of modern turbofans with high bypass ratios, whose diameter and circumferential speeds are increasingly growing. The rotational symmetry of the blade arrangements is particularly interesting in this context, both for aerodynamics and for the structure.

For high-aspect-ratio wings and future generations of engines, it is therefore necessary to control the aeroelastic phenomena that occur in the critical region. The University of Stuttgart, the Technical University of Berlin, the Technical University of Braunschweig, the Technical University of Munich, RWTH Aachen University, the University of the Bundeswehr Munich, and the German Aerospace Center are jointly investigating various measures, both numerically and experimentally, to make aviation more environmentally friendly and to expand the flight envelope of future commercial aircraft.

Research in this Joint Project:

Flutter is a complex aeroelastic phenomenon characterized by nonlinear effects. A deep understanding of the aerodynamic and aeroelastic effects is required for both wing and fan rotor design. In experimental investigations in the wind tunnel, not only the flow variables but also the time-dependent deformations and deflections of the model must be determined. In addition, it must be ensured that the model under investigation is not influenced by scaling or wind tunnel effects. For time-resolved numerical investigations, a fluid solver (CFD) must be coupled with a structural model. Since this coupling greatly increases the complexity and computational effort, a linearized system analysis based on the aerodynamic response to a geometric deformation can be performed as an approximation. Each method is subject to its own assumptions and simplifications. The results of the different approaches are used for comparison and validation.

The University of Stuttgart, RWTH Aachen University, and TU Berlin are investigating the potential for shifting the flutter boundary by applying bumps to the surface of the wing or fan rotor. These local contour bumps on the upper surface of the wing enable to control the supersonic domain and thus also the pressure distribution and the pitching moment of the wing or fan rotor blade. This altered pressure distribution has a direct effect on the coupled fluid-structure system. Based on preliminary work carried out by the project partners on the effects of bumps, it can be assumed that this will shift the limits of the operating range to higher speeds and angles of attack. For the wing, the OAT15A airfoil (known for studies on the related phenomenon of buffeting) and the DLR-F25 configuration are being considered in SaFuMa. NACA sections and the NASA Rotor 67 configuration are used for the fan rotor. Both RANS calculations and scale-resolving simulations are applied in the numerical investigations. Wind tunnel experiments are carried out in parallel to validate the results.

Together with the University of the Bundeswehr Munich, the Technical University of Munich is pursuing an approach to improve the flutter characteristics of the wing using control surfaces. Using flap deflections of spoilers and wing trailing edge flaps, it is also possible to influence the shock characteristics on the upper side of the wing. Similar to the effect of bumps, this should result in a wing geometry with a higher flutter limit than that of the reference wing. Both numerical simulations and wind tunnel experiments are being carried out.

The Institute of Aeroelasticity at the German Aerospace Center plays a central role in the field of flutter analysis. Together with the results from the other project partners, linearized analyses and modal structural models are used to determine the flutter boundary.

Several industrial partners support SaFuMa with their many years of experience and their connection to industrial practice and are available for consultation.

Individual Project Description:

RWTH Numerisches Teilprojekt:

In a numerical subproject, passive flutter suppression by fluidic and geometric shock control bumps (SCBs) are investigated using high-resolution numerical methods. For this purpose, the influence of SCBs on the shock/boudnary layer interaction, the shock-induced separation and the resulting forces, which are decisive for the flutter behavior, are analyzed. First, wall-resolved and wall-modeled Large-eddy simulation (LES) of the OAT15A profile are performed with selected SCB configurations. The SCBs to be investigated and the corresponding flow conditions are selected in cooperation with the project partners. This is supplemented by simulations with oscillations imposed on the profile. The results of this simulation will be used to evaluate the effectiveness and efficiency of the SCB configurations investigated. In addition, the data will be made available to the project partners for mutual validation of simulation and measurement results. In the next step, the influence of selected SCBs on the flutter characteristics of a highly stretched wing will be investigated. For this purpose, wall-modeled LES of the DLR F25 will be carried out in a rigid configuration and under imposed oscillations.

RWTH Experimente:

In complementary investigations in AIA’s Trisonic wind tunnel, the flutter control effect of fluidic and geometric SCBs is investigated experimentally. Wind tunnel experiments are first carried out on a rigid profile with and without SCBs. The resulting data will also be used by the project partners to validate the numerical method. Later on, oscillations are applied to the profile under investigation in the wind tunnel. These investigations are supplemented by experiments on a swept 3D wing. 

RWTH Numerisches Teilprojekt + Experimente:

Finally, experimental and numerical results are brought together to evaluate aerodynamic effects of the SCBs and their influence on the flutter boundary. 

Team

• Univ.-Prof. Dr. sc. Dominik Krug, +49 241 80-95410, d.krug[a⁤t]aia.rwth-aachen.de
• Dr.-Ing. Matthias Meinke, +49 241 80 95328, m.meinke[a⁤t]aia.rwth-aachen.de

Projektpartner

RWTH Aachen University: Chair of Fluid Mechanics and Institute of Aerodynamics

TU München: Institut für Aerodynamik und Strömungsmechanik

TU Berlin: Institut für Luft- und Raumfahrt (Ist das richtig? Oder lieber direkt Fachbereich Luftfahrtantriebe?)

Universität der Bundeswehr München: Institut für Strömungsmechanik und Aerodynamik

Deutsches Zentrum für Luft- und Raumfahrt e.V.: Institut für Aeroelastik

Antragsteller/Innen SaFuMa

Universität Stuttgart:

• Dr.-Ing. Thorsten Lutz, +49 711 685 63406, lutz@iag.uni-stuttgart.de
• Prof. Dr.-Ing. Andrea Beck, +49 711 685 60218, beck@iag.uni-stuttgart.de

RWTH Aachen:

• Univ.-Prof. Dr. sc. Dominik Krug, +49 241 80-95410, d.krug[a⁤t]aia.rwth-aachen.de
• Dr.-Ing. Matthias Meinke, +49 241 80 95328, m.meinke[a⁤t]aia.rwth-aachen.de

HS München (assoziiert):

• Prof. Dr.-Ing. Anne-Marie Schreyer, +49 89 1265-4492, anne-marie.schreyer@hm.edu

TU München:

• Prof. Dr.-Ing. habil. Christian Breitsamter, +49 (89) 289 – 16137, christian.breitsamter@tum.de

TU Berlin:

• Prof. Dr.-Ing. Dieter Peitsch, +49 30 314 22878, dieter.peitsch@tu-berlin.de

Universität der Bundeswehr München:

• PD Dr. rer. nat. habil. Sven Scharnowski, +49 89 6004-2273, sven.scharnowski@unibw.de

Deutsches Zentrum für Luft- und Raumfahrt e.V.:

• Prof. Dr.-Ing. Lorenz Tichy, +49 551 709 2341, lorenz.tichy@dlr.de
• Jens Nitzsche, 0551 / 709 2375, jens.nitzsche@dlr.de