On the fluid-structure interaction of flexible membrane wings for MAVs in and out of ground-effect

Abstract

Wind tunnel experiments are conducted at a Reynolds number of Re = 56,000, measuring rigid flat-plates and flexible membrane wings from free-flight into ground-effect conditions. Load cell measurements, digital image correlation and particle image velocimetry are applied in high-speed to resolve time-synchronised lift, drag and pitch oscillations simultaneously with membrane and flow dynamics. Proper orthogonal decomposition is applied on flow oscillations to determine their spatiotemporal evolution. Loads, membrane motions and flow dynamics are correlated to each other to investigate their underlying coupling physics. A membrane wing's ability of static cambering and dynamic membrane oscillations are found to be beneficial when the wing is in ground-effect, where the descent in height forces premature leading-edge vortex-shedding and drag increase. The dynamic motions of membrane wings help to exploit vortex-shedding dynamics from the leading-edge that ensures time-averaged reattached flow over the wing upper surface, resulting in further lift enhancement. Membrane wings show lag-free fluid-membrane coupling at peak-lift conditions. In post-stall conditions, the membrane is found to lag the flow dynamics, signalling the end of direct fluid-structure coupling.

Experimental analysis of a strong fluid–structure interaction on a soft membrane—Application to the flapping of a yacht downwind sail

“…This physical interpretation takes inspiration in Connell and Yue (2007) with the description of the snapping event of a flag, where similarly there is a peak of tension during the strong acceleration which is associated with a shedding of strong vortices. For 2D membranes, Rojratsirikul et al (2011) also present reduced frequencies similar to the ones found in the present work (see Table 1), confirmed by Bleischwitz et al (2017). They suggest that the membrane vibrations might be coupled with the first harmonic of the natural vortex shedding frequency at high incidence.…”

Assessing the Impact of Membrane Deformations on Wing Sail Performance

“…Research in this field has shown that membrane wings can have a steeper lift slope as well as higher/smoother stall angles and an overall higher performance due to the fluid structure interaction (Arbos Torrent 2013;Rojratsirikul 2010;Fairuz et al 2016;Gordnier, and Attar, 2014;. The unsteady effects of the membrane vibrations can also affect separated regions of flow, significantly changing the foil's performance (Rojratsirikul, 2010;Bleischwitz et al, 2017).…”

Analysis of fluid and solid interaction of the flexible bionic wing in ground effect

“…Bleischwitz et al. 17 studied the fluid–solid coupling phenomenon of flexible plates under-ground effect by experiments and concluded that the locomotion performances of flexible plates under ground effect are better than those of rigid plates. Quinn et al.…”

“…So far there have been many studies on the ground effect of airfoil and fluid–solid interaction of flexible thin plates and airfoils. 2–18 Previous studies have shown that the presence of ground effects can lead to an increase in lift, and flexible airfoils and thin plates generally have better locomotion performance over rigidity. However, no work has systematically studied the effect of flexibility changes on the characteristics of the force and deformation of the flexible wing.…”