52 research outputs found
Simulations of propelling and energy harvesting articulated bodies via vortex particle-mesh methods
The emergence and understanding of new design paradigms that exploit flow
induced mechanical instabilities for propulsion or energy harvesting demands
robust and accurate flow structure interaction numerical models. In this
context, we develop a novel two dimensional algorithm that combines a Vortex
Particle-Mesh (VPM) method and a Multi-Body System (MBS) solver for the
simulation of passive and actuated structures in fluids. The hydrodynamic
forces and torques are recovered through an innovative approach which crucially
complements and extends the projection and penalization approach of Coquerelle
et al. and Gazzola et al. The resulting method avoids time consuming
computation of the stresses at the wall to recover the force distribution on
the surface of complex deforming shapes. This feature distinguishes the
proposed approach from other VPM formulations. The methodology was verified
against a number of benchmark results ranging from the sedimentation of a 2D
cylinder to a passive three segmented structure in the wake of a cylinder. We
then showcase the capabilities of this method through the study of an energy
harvesting structure where the stocking process is modeled by the use of
damping elements
Three-dimensional soft streaming
Viscous streaming is an efficient rectification mechanism to exploit flow
inertia at small scales for fluid and particle manipulation. It typically
entails a fluid vibrating around an immersed solid feature that, by
concentrating stresses, modulates the emergence of steady flows of useful
topology. Motivated by its relevance in biological and artificial settings
characterized by soft materials, recent studies have theoretically elucidated,
in two dimensions, the impact of body elasticity on streaming flows. Here, we
generalize those findings to three dimensions, via the minimal case of an
immersed soft sphere. We first improve existing solutions for the rigid sphere
limit, by considering previously unaccounted terms. We then enable body
compliance, exposing a three-dimensional, elastic streaming process available
even in Stokes flows. Such effect, consistent with two-dimensional analyses but
analytically distinct, is validated against direct numerical simulations and
shown to translate to bodies of complex geometry and topology, paving the way
for advanced forms of flow control
Optimal shapes for anguilliform swimmers at intermediate Reynolds numbers
We investigate the optimal morphologies for fast and efficient anguilliform swimmers at intermediate Reynolds numbers, by combining an evolution strategy with three-dimensional viscous vortex methods. We show that anguilliform swimmer shapes enable the trapping and subsequent acceleration of regions of fluid transported along the entire body by the midline travelling wave. A sensitivity analysis of the optimal morphological traits identifies that the width thickness in the anterior of the body and the height of the caudal fin are critical factors for both speed and efficiency. The fastest swimmer without a caudal fin, however, still retains 80 % of its speed, showing that the entire body is used to generate thrust. The optimal shapes share several features with naturally occurring morphologies, but their overall appearances differ. This demonstrates that engineered swimmers can outperform biomimetic swimmers for the criteria considered her
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