Aerodynamic investigation for a coupling process of two wings

• Applicant: Dr.-Ing. Thomas Grund
• Subject Area: Fluid Mechanics
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 511042382

In recent years, efforts have been made to develop unmanned aerial vehicles as pseudo-satellites in the stratosphere. One design goal of such aircraft is a long flight time of up to one year, which requires a very low energy consumption. This requirement results in very high demands on the structure and aero-dynamics of the aircraft configuration. From a structural perspective, such an aircraft should be as light as possible but also withstand heavy loads. To reach mission altitude, the aircraft must fly through the troposphere, which feature severe atmospheric disturbances that impose further demands on the struc-ture aerodynamically, a highly efficient design is important to minimize power consumption. This can be reached through a laminar wing section and a large aspect ratio, though the latter requirement neces-sarily limits the loads that the structure can bear. One potential approach to achieve these contradicto-ry requirements is the multi body configuration, whereby several individual aircraft are coupled at their wing tips. Each aircraft takes off alone and flies to mission altitude, where they are coupled together to form one aircraft with a large aspect ratio.Therefore, the aim of the proposal is to identify and quantify the complex fluid mechanical processes that occur when approaching two wings. The viscous vortex systems interacting in such a process are very much dependent on the distance and angle of attack of the wings and on the selected coupling trajectory. The influence of these parameters on the aerodynamically averaged and time-resolved pa-rameters as well as on the forming vortex structures will be investigated in detail temporally and spa-tially to gain new insights into the interaction as a function of the variation parameters.Based on existing preliminary results with on a generic wing configuration as well as first investigations on two laminar airfoils, laminar airfoils with integrated ailerons will be investigated in the proposed project. For the wind tunnel tests, a model consisting of two individual wings will be designed and man-ufactured in order to allow a variation of angles of attack, wing distances and coupling path. The de-termination of the aerodynamic characteristics will be carried out with a 6-component balance and static pressure tap rows at different wing spanwise positions. Furthermore, flow field measurements will be carried out to investigate the interaction of the resulting wing-tip vortices by means of a stereo-scopic Time-Resolved Particle Image Velocimetry system (sTR-PIV) in order to obtain a better under-standing of the flow physics of this highly transient process. In addition, the results will be incorporated into a database. The database will be used to determine parameter configurations with small load changes, which require low control forces for the coupling process. This data can be used, for example, to design controllers for flight attitude stabilization during coupling events.

• DFG Programme: Research Grants