Immersed boundary simulations of flows driven by moving thin membranes

Lauber, Marin; Weymouth, Gabriel; Limbert, Georges

doi:10.1016/j.jcp.2022.111076

Cited by 10 publications

(21 citation statements)

References 35 publications

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“…We perform all the simulations with our validated fluid-structure interaction solver [29, 30] which couples an immersed boundary finite volume method for the fluid with a shell finite element method for the structure. Defining b as the hand-wing span, the fluid domain consists of a uniform region of dimensions [2.5, 1.2, 1.2] × b , centered around the wing.…”

Section: Methodsmentioning

confidence: 99%

Rapid flapping and fiber-reinforced membrane wings are key to high-performance bat flight

Lauber,

Weymouth,

Limbert

2023

Preprint

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Bats fly using significantly different wing motions than other fliers, stemming from the complex interplay of their membrane wings' motion and structural properties. Biological studies show that many bats fly at Strouhal numbers, the ratio of flapping to flight speed, 50-150% above the range typically associated with optimal locomotion. We use high-resolution fluid-structure interaction simulations of a bat wing to independently study the role of kinematics and material/structural properties on aerodynamic performance and show that peak propulsive and lift efficiencies for a bat-like wing motion require flapping 66% faster than for a bird-like motion, agreeing with the increased flapping frequency observed in zoological studies. In addition, we find that reduced membrane stiffness is associated with improved propulsive efficiency until the membrane flutters, but that incorporating microstructural anisotropy arising from biological fiber reinforcement enables a tenfold reduction of the flutter energy whilst maintaining high aerodynamic efficiency. Our results indicate that animals with specialized flapping motions may have correspondingly specialized flapping speeds, in contrast to arguments for a universally efficient Strouhal range. Additionally, our study demonstrates the significant role that the microstructural constitutive properties of the membrane wing of a bat can have on its propulsive performance.

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Section: Methodsmentioning

confidence: 99%

Rapid flapping and fiber-reinforced membrane wings are key to high-performance bat flight

Lauber,

Weymouth,

Limbert

2023

Preprint

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“…Temporal discretisation is achieved via Heun's explicit second-order method and an adaptive time-stepping scheme is used to preserve stability (Polet, Rival, & Weymouth, 2015). Moreover, turbulence is described through an implicit large eddy simulation (iLES) model that uses flux limiting to model the energy dissipation caused by sub-grid stress (Lauber, Weymouth, & Limbert, 2022). iLES modelling is well suited to intermediate Reynolds numbers such as those used in the present study, and (Hendrickson, Weymouth, Yu, and Yue (2019)) demonstrates that this iLES model completely deactivates when the grid is sufficiently fine to resolve the physical dissipation.…”

Section: Methodsmentioning

confidence: 99%

Effect of aspect ratio on the propulsive performance of tandem flapping foils

Lagopoulos

Weymouth

Ganapathisubramani

2023

Flow

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In this work, we describe the impact of aspect ratio ( $AR$ ) on the performance of optimally phased, identical flapping flippers in a tandem configuration. Three-dimensional simulations are performed for seven sets of single and tandem finite foils at a moderate Reynolds number, with thrust producing, heave-to-pitch coupled kinematics. Increasing slenderness (or $AR$ ) is found to improve thrust coefficients and thrust augmentation but the benefits level off towards higher values of $AR$ . However, the propulsive efficiency shows no significant change with increasing $AR$ , while the hind foil outperforms the single by a small margin. Further analysis of the spanwise development and propagation of vortical structures allows us to gain some insights into the mechanisms of these wake interactions and provide valuable information for the design of novel biomimetic propulsion systems.

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“…2019). We use an adaptive time step based on the Courant–Friedrichs–Lewy condition that has been shown to converge with (Lauber, Weymouth & Limbert 2022).…”

Section: Methodsmentioning

confidence: 99%

“…The undulating plate was coupled to these flow equations using the boundary data immersion method (BDIM) formulated in Weymouth & Yue (2011) and developed further for higher Reynolds numbers in Maertens & Weymouth (2015) and thin geometries in Lauber et al. (2022). The BDIM enforces the boundary condition on the body by convolving together the fluid and body governing equations on a Cartesian background grid.…”

Section: Methodsmentioning

confidence: 99%

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A systematic investigation into the effect of roughness on self-propelled swimming plates

Massey,

Ganapathisubramani,

Weymouth

2023

J. Fluid Mech.

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This study examines the effects of surface topography on the flow and performance of a self-propelled swimming (SPS) body. We consider a thin flat plate with an egg-carton roughness texture undergoing prescribed undulatory swimming kinematics at Strouhal number $0.3$ and tail amplitude to length ratio $0.1$ ; we use plate Reynolds numbers $Re=6$ , 12 and $24\times 10^3$ , and focus on $12\,000$ . As the roughness wavelength is decreased, we find that the undulation wave speed must be increased to overcome the additional drag from the roughness and maintain SPS. Correspondingly, the extra wave speed raises the power required to maintain SPS, making the swimmer less efficient. To decouple the roughness and the kinematics, we compare the rough plates to equivalent smooth cases by matching the kinematic conditions. We find that all but the longest roughness wavelengths reduce the required swimming power and the unsteady amplitude of the forces when compared to a smooth plate undergoing identical kinematics. Additionally, roughness can enhance flow enstrophy by up to 116 % compared to the smooth cases without a corresponding spike in forces; this suggests that the increased mixing is not due to increased vorticity production at the wall. Instead, the enstrophy is found to peak strongly when the roughness wavelength is approximately twice the boundary layer thickness over the $Re$ range, indicating the roughness induces large-scale secondary flow structures that extend to the edge of the boundary layer. This study reveals the nonlinear interaction between roughness and kinematics beyond a simple increase or decrease in drag, illustrating that roughness studies on static shapes do not transfer directly to unsteady swimmers.

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Immersed boundary simulations of flows driven by moving thin membranes

Cited by 10 publications

References 35 publications

Rapid flapping and fiber-reinforced membrane wings are key to high-performance bat flight

Rapid flapping and fiber-reinforced membrane wings are key to high-performance bat flight

Effect of aspect ratio on the propulsive performance of tandem flapping foils

A systematic investigation into the effect of roughness on self-propelled swimming plates

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