Analysis of the influence of skeletal membrane wing configurations on fluid-structure interaction mechanisms

This study investigates the skeletal framework configurations for membrane wings, specifically focusing on batten arrangements and their role in imparting chordwise cross-sectional camber. Wind tunnel experiments were conducted at Re = 2.4 × 10⁴ (based on chord length, corresponding to a freestream velocity of U _∞ = 5 m/s) over an α range of 0° to 20° at 2° increments to characterize aerodynamic forces, with unsteady membrane deformation measurements additionally performed at α = 10° using digital image correlation techniques. Complementary unsteady numerical simulations using a coupled fluid-structure solver were performed at selected α = 4°, 10°, and 16° under otherwise identical conditions to resolve the time-varying flow fields and membrane responses. Fourier mode decomposition analysis was applied to both experimental and numerical data to extract dominant vibration and pressure fluctuation modes. Wings with 0 to 5 battens and cross-sections based on a flat plate or the E387 profile mean camber line were examined. The influence of the skeletal structure on aerodynamic performance was assessed, and fluid-structure interaction (FSI) mechanisms were systematically compared for configurations with and without battens and camber. Key findings indicate that cambered membrane wings generate higher lift and L/D , with lift improvements exceeding 40% and L/D improvements exceeding 10% at low α compared to flat wings, albeit with increased nose-down pitching moments. The addition of battens reduces the nose-down pitching moment, enhances pitch stability, and improves L/D at low α by suppressing vibration amplitudes by up to 37% through structural stiffening. However, this stiffening comes at the cost of attenuated fluid-structure coupling benefits at higher α ( α > 10°), resulting in an 8% to 12% reduction in the C_L . Analysis of the similarity in their modal shapes within the coupled system's dominant frequency facilitated the investigation of FSI mechanisms: batten-free membrane wings exhibited specific-frequency membrane vibrations driving separation bubble motion and modulating vortex shedding to influence aerodynamic force characteristics. For membrane wings with battens, it is speculated that the coupling involves three-dimensional effects from tip vibrations interacting with local vortex structure alterations along the span from the tip towards the mid-span region.