FluSI: A Novel Parallel Simulation Tool for Flapping Insect Flight Using a Fourier Method with Volume Penalization

Engels, Thomas; Kolomenskiy, Dmitry; Schneider, Kai; Sesterhenn, Jörn

doi:10.1137/15m1026006

Cited by 50 publications

(86 citation statements)

References 34 publications

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“…To conduct the simulation, we designed a 'numerical wind tunnel' and placed the animal in a 6R × 4R × 4R large, virtual, rectangular box, where R = 13.2 mm is the wing length. The computational domain is discretized with 680 million grid points and the incompressible three-dimensional Navier-Stokes equations are solved by direct numerical simulation [10]. An imposed mean inflow velocity accounts for the forward flight speed of the tethered insect, with superimposed velocity fluctuations in the turbulent cases.…”

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confidence: 99%

Bumblebee Flight in Heavy Turbulence

et al. 2016

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High-resolution numerical simulations of a tethered model bumblebee in forward flight are performed superimposing homogeneous isotropic turbulent fluctuations to the uniform inflow. Despite tremendous variation in turbulence intensity, between 17% and 99% with respect to the mean flow, we do not find significant changes in cycle-averaged aerodynamic forces, moments or flight power when averaged over realizations, compared to laminar inflow conditions. The variance of aerodynamic measures, however, significantly increases with increasing turbulence intensity, which may explain flight instabilities observed in freely flying bees.Insect flight currently receives considerable attention from both biologists and engineers. This growing interest is fostered by the recent trend in miniaturization of unmanned air vehicles that naturally incites reconsidering flapping flight as a bio-inspired alternative to fixed-wing and rotary flight. For all small flyers it is challenging to fly outdoors in an unsteady environment, and it is essential to know how insects face that challenge.Field studies show variations of insect behavior with changing weather conditions, including the atmospheric turbulence [1]. Earlier laboratory research on aerodynamics of insect flight assumed quiescent air, and only some more recent experiments focused on the effect of different kinds of unsteady flows. The behavior of orchid bees flying freely in a turbulent air jet has been studied in [2]. The authors found that turbulent flow conditions have a destabilizing effect on the body, most severe about the animal's roll axis. In response to this flow, bees try to compensate the induced moments by an extension of their hindlegs, increasing the roll moment of inertia. Interaction of bumblebees with wake turbulence has also been considered in [3]. These experiments were performed in a von Kármán-type wake behind cylinders. The bees displayed large rolling motions, pronounced lateral accelerations, and a reduction in their upstream flight speed. In [4] a comparative study on the sensitivity of honeybees and stalk-eye flies to localized wind gusts was performed. The study found that bees and stalkeye flies respond differently to aerial perturbations, either causing roll instabilities in bees or significant yaw rotations in stalk-eye flies. In [5] feeding flights of hawkmoths in vortex streets past vertical cylinders were analyzed. Depending on distance of the animal from the cylinder and cylinder size, destabilizing effects on yaw and roll and a reduction in the animal's maximum flight speed have been observed. Kinematic responses to large helical coherent structures were also found in hawkmoths flying in a vortex chamber [6]. A study on the energetic significance of kinematic changes in hummingbird feeding flights further demonstrated a substantial increase in metabolic rate during flight in turbulent flows, compared to flight in undisturbed laminar inflow [7,8]. All studies reported significant changes in the behavior of insects when they fly in turbulent...

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confidence: 99%

Bumblebee Flight in Heavy Turbulence

et al. 2016

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“…where f is some parametric form for the solids we wish to study. We note that h is proportional to the grid size, ∆x, and as ∆x → 0 the function χ i tends to a Heaviside function [28].…”

Section: Numerical Implementation Of Masksmentioning

confidence: 94%

“…The starting point for the discretization of the penalized governing equations is the open-source software FluSI [28], a Fourier pseudo-spectral code for fluid-structure interactions. It solves the three-dimensional, incompressible Navier-Stokes equations on equispaced grids using a spectral formulation, adaptive time-stepping and a pressure-projection approach.…”

Section: Methodsmentioning

confidence: 99%

A gradient-based framework for maximizing mixing in binary fluids

Eggl

Schmid

2018

Journal of Computational Physics

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A computational framework based on nonlinear direct-adjoint looping is presented for optimizing mixing strategies for binary fluid systems. The governing equations are the nonlinear Navier-Stokes equations, augmented by an evolution equation for a passive scalar, which are solved by a spectral Fourier-based method. The stirrers are embedded in the computational domain by a Brinkmanpenalization technique, and shape and path gradients for the stirrers are computed from the adjoint solution. Four cases of increasing complexity are considered, which demonstrate the efficiency and effectiveness of the computational approach and algorithm. Significant improvements in mixing efficiency, within the externally imposed bounds, are achieved in all cases.

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“…Gimbal lock occurs when two rotation axis become parallel and the system looses one degree of freedom. The detailed set of 13 first-order ODEs can be found in [20]. In both free and tethered flight, we prescribe an identical wing motion relative to the body, as illustrated in Fig.…”

Section: Bumblebee Modelmentioning

confidence: 99%

Impact of turbulence on flying insects in tethered and free flight: High-resolution numerical experiments

et al. 2019

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Flapping insects are remarkably agile fliers, adapted to a highly turbulent environment. We present a series of high resolution numerical simulations of a bumblebee interacting with turbulent inflow. We consider both tethered and free flight, the latter with all six degrees of freedom coupled to the Navier-Stokes equations. To this end we vary the characteristics of the turbulent inflow, either changing the turbulence intensity or the spectral distribution of turbulent kinetic energy. Active control is excluded in order to quantify the passive response real animals exhibit during their reaction time delay, before the wing beat can be adapted. Modifying the turbulence intensity shows no significant impact on the cycle-averaged aerodynamical forces, moments and power, compared to laminar inflow conditions. The fluctuations of aerodynamic observables, however, significantly grow with increasing turbulence intensity. Changing the integral scale of turbulent perturbations, while keeping the turbulence intensity fixed, shows that the fluctuation level of forces and moments is significantly reduced if the integral scale is smaller than the wing length. Our study shows that the scale-dependent energy distribution in the surrounding turbulent flow is a relevant factor conditioning how flying insects control their body orientation. * thomas.engels@ens.fr arXiv:1901.10350v1 [physics.flu-dyn] 29 Jan 2019Insect are fast and agile fliers, which stabilize their body posture during flight under a vast variety of environmental conditions [5,37]. While flight in static air requires little steering and corrective changes in aerodynamic force production, flight in turbulent air is challenged by unexpected changes in flow conditions at the body and wings. Little is known about the impact of turbulence on the aerodynamic performance and energetic cost of flight in insects. In this work, we study how different kinds of perturbations affect flapping fliers in free flight.In contrast to laminar flows, turbulent flows are dominated by nonlinear interactions and, as a result, excite fluctuations on a wide range of scales. After averaging the flow in either ensemble, time or space, we identify different length scales characteristic for the turbulent regime. From large to small, these classical scales are: (i) the integral scale Λ where, on average, the velocity the strongest, and where therefore energy transport is most active, (ii) the Taylor microscale λ where, on average, the velocity gradients are most intense, (iii) the Kolomogorov scale η below which, on average, the flow fluctuations are damped by the fluid viscosity [47].In nature, unsteady turbulent flow conditions significantly vary depending on the terrain and weather conditions. The "flight boundary layer", characterized by conditions favorable for insect flight, can span for up to 1500 meters above the ground level in warm weather [6]. Activity such as long-distance migration is typical of high altitudes while foraging, for example, mainly takes place in the vegetation layer up...

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FluSI: A Novel Parallel Simulation Tool for Flapping Insect Flight Using a Fourier Method with Volume Penalization

Cited by 50 publications

References 34 publications

Bumblebee Flight in Heavy Turbulence

Bumblebee Flight in Heavy Turbulence

A gradient-based framework for maximizing mixing in binary fluids

Impact of turbulence on flying insects in tethered and free flight: High-resolution numerical experiments

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