Unsteady aerodynamics of adaptive elasto-flexible membrane wing
Final Report Abstract
During the project, a new full model with elasto-flexible membrane wings was designed and constructed. The wing planform can be changed actively by varying the aspect ratio and the wing sweep over a wide range. In addition, the model is equipped with an elastic membrane, which is capable of adapting to aerodynamic loads. The experimental investigations indicate the potential of the elasto-flexible morphing wing. Depending on the flight stage, various flight characteristics can be achieved by one single configuration. In addition, the airfoil passively adapts by a change in thickness distribution and camber to the aerodynamic loads of the inflow resulting in an extension of attached flow and smooth stall conditions. The results of the force and moment measurements show the expected improvement of the maximum lift-todrag ratio with an increasing aspect ratio. Furthermore, the aerodynamic coefficients indicate a significant variation concerning the lift and the drag characteristics for different wing positions. The Reynolds number mainly influences the configurations with high aspect ratios. Asymmetric wing configurations deliver significant rolling moments, which can be used for an active control of the aircraft. In the high lift regime, the wake of the model is investigated by Stereo-PIV measurements. The High Aspect ratio Configuration (HAC) shows areas with separated flow, while the flow at the Highly Swept Configuration (HSC) stays attached at higher angles of attack. The lift distribution varies with the wing position. While the HSC generates more lift in the wing tip region, the HAC shows a more elliptical distribution. The DIC measurements exhibit an increasing deformation with higher angles of attack. Especially, the area close to the fuselage is affected. The airfoil shapes in this area show an increasing camber and thickness. The HSC deforms stronger than the HAC due to the lower pre-strain and the increasing local wing root, which is one reason for the smoother and delayed stall region of the swept one. For the measurements at unsteady inflow conditions a new gust generator was designed, constructed and validated. The flow field measurements above the wings show the separation behavior during the impact of the one-minus-cosine gust. In the wake, the development of the shear layer, the wing tip vortex and their interaction are observed. The deformation measurements detect the positive deflection of the upper membrane during the gust which leads to an increasing camber and thus, more lift. Parallel to the experimental work the membrane wing is investigated by fluid-structure-interaction simulations. With the large experimental data set, the simulations can now be validated. The numerical results allow a more detailed view into the flow field. A lot of simulations have already been carried out for stationary cases and first simulations with a gust moving through the domain show good results, but still need some adjustments. By those simulations the differences between a rigid wing and a membrane wing can be determined which will show if the membrane can alleviate the gust loads compared to a "rigid" wing in the manner of a “low-pass” filter. In addition, the evaluation of the structural results will show if the membrane can have positive influence on the aeroelastic behavior of the wing.
Publications
- “Extended flexible trailing-edge on the flow structures of an airfoil at high angle of attack,” Experiments in Fluids, Vol. 60, No. 122, 2019
He, X., Guo, Q., and Wang, J.
(See online at https://doi.org/10.1007/s00348-019-2767-5) - “Experimental investigations of a full model with elasto-flexible membrane wings,” Chinese Journal of Aeronautics, Vol. 34, No. 7, 2020, pp. 211–218
Pflüger, J., and Breitsamter, C.
(See online at https://doi.org/10.1016/j.cja.2020.03.037) - “Fluid–structure interaction of a flexible membrane wing at a fixed angle of attack,” Physics of Fluids, Vol. 32, No. 12, 2020, p. 127102
He, X., and Wang, J.
(See online at https://doi.org/10.1063/5.0029378) - Aerodynamic Analysis of a full model with adaptive elastoflexible membrane wings. 32th ICAS Congress 2020/21 - Shanghai, China
Pflüger J., Hirschmann K. and Breitsamter C.
- Deformation Measurements of a Full Span Model with Adaptive Elasto-Flexible Membrane Wings, Springer International Publishing, 2021, Vol. 151, Chap. Notes on Numerical Fluid Mechanics and Multidisciplinary Design
Pflüger, J., Chen, Y., and Breitsamter, C.
(See online at https://doi.org/10.1007/978-3-030-79561-0_51) - “Effects of wing flexibility on aerodynamic performance of an aircraft model,” Chinese Journal of Aeronautics, Vol. 34, No. 9, 2021, pp. 133–142
Guo, Q., He, X., Wang, Z., and Wang, J.
(See online at https://doi.org/10.1016/j.cja.2021.01.012) - “Flow Field and Deformation Measurements of a Membrane Wing for Unsteady Inflow Conditions”, AIAA Aviation Forum, 2022 (Control ID 3688514)
Pflüger, J., and Breitsamter, C.
