Individual Project Description

The University of Stuttgart investigates the potential of contour bumps on the upper surface of wings to reduce flutter. To achieve this, process chains for 2D and 3D cases are being developed that can be used to design bumps on airfoils and wings. Based on preliminary work on flutter analysis, the bumps are initially designed taking into account the stationary aerodynamic coefficients and their gradients. In the next step, unsteady calculations are used to investigate forced impulse movements, which enable a linearized flutter analysis to be performed. To validate these methods, structure-coupled, time-resolved calculations needed. To do this, the structural movements of the bodies are reduced to their relevant modes. The findings are then used to consider a realistic case in which a bump is designed for three-dimensional swept wing with high aspect ratio and span. The effectiveness of the bumps in increasing the flutter boundary is quantified. To enable further investigations and industrial applications of this approach, empirical design guidelines for generalized applications are developed.

In this subproject, we are investigating the mode of action as well as the efficacy of different semi-active measures for flutter suppression on transonic fan blades used in modern aeroengines. The primary focus of research is on contour modifications ("bumps"). The particular challenge of compressors in comparison to wings lies in the periodicity constraints resulting from flow coupling in the direction of rotation. Based on preliminary work and in collaboration with our project partners, we will first analyze suitable designs and relevant operating points that are likely to be prone to flutter. Initial configurations of these bumps will then be derived. High-fidelity unsteady large-eddy simulations are performed for the blades with and without bumps, which provide accurate predictions of the shock-boundary layer interaction and serve to validate the design approaches based on RANS methods. Subsequently, unsteady calculations are used to investigate forced impulse excitations, which enable a linearized flutter analysis. In order to capture nonlinear coupling effects, fluid-structure interaction simulations are subsequently conducted, in which the structural dynamics are represented by a modal approach on a reduced basis. The results obtained in this way can then be used to derive limit cycle vibrations and, as a consequence, to develop design guidelines for shock control bumps intended for industrial use.