Structural Design of a Shock Control Bump for a Natural Laminar Flow Aircraft Wing

Abstract

To reduce emissions and fuel consumption in aviation the laminar wing technology promises a high potential due to distinctly lower drag compared to conventional turbulent wings. Morphing structures offer a great potential in adapting the wing shape during flight with respect to changing flow conditions and, in addition, reduce negative effects of gaps and steps of conventional movable wing devices on the laminar flow behaviour. Besides high-lift concepts like the Smart Droop Nose technology [1] the reduction of wave drag during transonic flights is one promising approach for reducing fuel consumption and emissions in aviation. At transonic flight conditions a transonic shock can occur which results in wave drag and increases the overall drag distinctly. One concept of reducing this wave drag is to generate a Shock Control Bump (SCB) which dissipates the single strong shock into several weaker isentropic compression waves resulting in drag benefits. The position of the main shock can change depending on flight conditions and, moreover, the buffeting effect can occur. SCBs not only offer a potential in fixing the shock position but also in buffet alleviation. Variable camber is one additional technology to fix the shock position and can interact well with SCBs. These phenomena have been investigated widely from an aerodynamic point of view, however, detailed structural and actuation concepts have not been discussed in depth. In the present work the challenge of varying shock position is approached by a morphing spoiler SCB concept with adaptive bump crest position and height. For this purpose, only one additional actuator is needed on the spoiler motivated by the need to mitigate complexity. Two rigid reinforced spoiler parts as well as two flexible sections are applied according to the technology of the flexible hinge introduced by KIRN et al. [2] to avoid mechanical hinges and gaps. Moreover, the trailing edge section of the spoiler is pre-shaped to realize a line contact force on the flap that prevents the spoiler from lifting up uncontrolled. This concept of the pre-shaped spoiler geometry was already introduced by Kirn and Machunze [2], [3]. A 2D FE-model is presented as well with the objective to identify the maximum forward and maximum backward position of the bump. The structural analysis focusses on the load cases cruise, maximum forward and backward position as well as the airbrake. The actuator forces are determined and the structural strength of the spoiler is assessed paying particular attention of the flexible hinge regions. Furthermore, experimental results of a 2D functional demonstrator are presented to evaluate the resulting contours of the spoiler. For this purpose, the GOM ATOS scanning system is used. Sources: [1] M. Kintscher, J. Kirn, and H. P. Monner, "Ground Test of an Enhanced Adaptive Droop Nose Device", presented at the ECCOMAS Congress 2016, Crete Island, Greece, 2016. [2] J. Kirn, W. Machunze, M. Weber, and F. Strachauer, "Non-discrete spoiler with an adaptive shock control bump", presented at the ICAST2016, Lake George, New York, USA, 2016. [3] W. Machunze, J. Kirn, and M. Weber, "Integral CFRP spoiler with shock bump control", presented at the 19th International Conference on Composite Structures, ICCS19, Porto, Portugal, 2016.