82 research outputs found
Moth-inspired navigation algorithm in a turbulent odor plume from a pulsating source
Some female moths attract male moths by emitting series of pulses of
pheromone filaments propagating downwind. The turbulent nature of the wind
creates a complex flow environment, and causes the filaments to propagate in
the form of patches with varying concentration distributions. Inspired by moth
navigation capabilities, we propose a navigation strategy that enables a flier
to locate a pulsating odor source in a windy environment using a single
threshold-based detection sensor. The strategy is constructed based on the
physical properties of the turbulent flow carrying discrete puffs of odor and
does not involve learning, memory, complex decision making or statistical
methods. We suggest that in turbulent plumes from a pulsating point source, an
instantaneously measurable quantity referred as a "puff crossing time",
improves the success rate as compared to the navigation strategy based on
"internal counter" that does not use this information. Using computer
simulations of fliers navigating in turbulent plumes of the pulsating point
source for varying flow parameters: turbulent intensities, plume meandering and
wind gusts, we obtained trajectories qualitatively resembling male moths
flights towards the pheromone sources. We quantified the probability of a
successful navigation as well as the flight parameters such as the time spent
searching and the total flight time, with respect to different turbulent
intensities, meandering or gusts. The concepts learned using this model may
help to design odor-based navigation of miniature airborne autonomous vehicles
Turbulent flow over a house in a simulated hurricane boundary layer
Every year hurricanes and other extreme wind storms cause billions of dollars
in damage worldwide. For residential construction, such failures are usually
associated with roofs, which see the largest aerodynamic loading. However,
determining aerodynamic loads on different portions of North American houses is
complicated by the lack of clear load paths and non-linear load sharing in wood
frame roofs. This problem of fluid-structure interaction requires both wind
tunnel testing and full-scale structural testing.
A series of wind tunnel tests have been performed on a house in a simulated
atmospheric boundary layer (ABL), with the resulting wind-induced pressures
applied to the full-scale structure. The ABL was simulated for flow over open
country terrain where both velocity and turbulence intensity profiles, as well
as spectra, were matched with available full scale measurements for this type
of terrain. The first set of measurements was 600 simultaneous surface pressure
measurements over the entire house.
A key feature of the surface pressure field is the occurrence of large,
highly non-Gaussian, peak uplift (suctions) on the roof. In order to better
understand which flow features cause this, PIV experiments were performed on
the wind tunnel model. These experiments were performed with time-resolved PIV
(sampling rate of 500 Hz) for a duration of 30 seconds. From the fluid dynamics
videos (low- and high-resolution) generated from the PIV data it is clear that
strong circulation is generated at the windward edge of the roof. These
vortices are eventually shed and convect along the roof. It is the presence of
this concentrated circulation which is responsible for the peak loading
observed.Comment: Abstract for Gallery of Fluid Motion 2009 in Minneapoli
Numerical Study of Owls\u27 Leading-edge Serrations
Owls\u27 silent flight is commonly attributed to their special wing morphology combined with wingbeat kinematics. One of these special morphological features is known as the leading-edge serrations: rigid miniature hook-like patterns found at the primaries of the wings\u27 leading-edge. It has been hypothesized that leading-edge serrations function as a passive flow control mechanism, impacting the aerodynamic performance. To elucidate the flow physics associated with owls\u27 leading-edge serrations, we investigate the flow-field characteristic around a barn owl wing with serrated leading-edge geometry positioned at 20° angle of attack for a Reynolds number of 40 000. We use direct numerical simulations, where the incompressible Navier–Stokes equations are solved on a Cartesian grid with sufficient resolution to resolve all the relevant flow scales, while the wing is represented using an immersed boundary method. We have simulated two wing planforms: with serrations and without. Our findings suggest that the serrations improve suction surface flow by promoting sustained flow reattachment via streamwise vorticity generation at the shear layer, prompting weaker reverse flow, thus augmenting stall resistance. Aerodynamic performance is negatively impacted due to the shear layer passing through the serration array, which results in altered surface pressure distribution over the upper surface. In addition, we found that serrations increase turbulence level in the downstream flow. Turbulent momentum transfer near the trailing edge increased due to the presence of serrations upstream the flow, which also influences the mechanisms associated with separation vortex formation and its subsequent development over the upper surface of the wing.
This article was published as Open Access through the CCU Libraries Open Access Publishing Fund. The article was first published in Physics of Fluids: https://doi.org/10.1063/5.017414
Exploration-Exploitation Model of Moth-Inspired Olfactory Navigation
Navigation of male moths toward females during the mating search offers a
unique perspective on the exploration-exploitation (EE) model in
decision-making. This study uses the EE model to explain male moth
pheromone-driven flight paths. We leverage wind tunnel measurements and 3D
tracking using infrared cameras to gain insights into male moth behavior.
During the experiments in the wind tunnel, we add disturbance to the airflow
and analyze the effect of increased fluctuations on moth flights in the context
of the proposed EE model. We separate the exploration and exploitation phases
by applying a genetic algorithm to the dataset of moth 3D trajectories. First,
we demonstrate that the exploration-to-exploitation rate (EER) increases with
distance from the source of the female pheromone, which can be explained in the
context of the EE model. Furthermore, our findings reveal a compelling
relationship between EER and increased flow fluctuations near the pheromone
source. Using the open-source pheromone plume simulation and our moth-inspired
navigation model, we explain why male moths exhibit an enhanced EER as
turbulence levels increase, emphasizing the agent's adaptation to dynamically
changing environments. This research extends our understanding of optimal
navigation strategies based on general biological EE models and supports the
development of advanced, theoretically supported bio-inspired navigation
algorithms. We provide important insights into the potential of bio-inspired
navigation models for addressing complex decision-making challenges
The role of leading-edge serrations in controlling the flow over owls’ wing
We studied the effects of leading-edge serrations on the flow dynamics developed over an owl wing model. Owls are predatory birds. Most owl species are nocturnal, with some active during the day. The nocturnal ones feature stealth capabilities that are partially attributed to their wing microfeatures. One of these microfeatures is small rigid combs (i.e. serrations) aligned at an angle with respect to the incoming flow located at the wings\u27 leading-edge region of the primaries. These serrations are essentially passive flow control devices that enhance some of the owls\u27 flight characteristics, such as aeroacoustics and, potentially, aerodynamics. We performed a comparative study between serrated and non-serrated owl wing models and investigated how the boundary layer over these wings changes in the presence of serrations over a range of angles of attack. Using particle image velocimetry, we measured the mean and turbulent flow characteristics and analyzed the flow patterns within the boundary layer region. Our experimental study suggests that leading-edge serrations modify the boundary layer over the wing at all angles of attack, but not in a similar manner. At low angles of attack ( \u3c 20° ), the serrations amplified the turbulence activity over the wing planform without causing any significant change in the mean flow. At 20° angle of attack, the serrations act to suppress existing turbulence conditions, presumably by causing an earlier separation closer to the leading-edge region, thus enabling the flow to reattach prior to shedding downstream into the wake. Following the pressure Hessian equation, turbulence suppression reduces the pressure fluctuations gradients. This reduction over the wing would weaken, to some extent, the scattering of aerodynamic noise in the near wake region.
This article was published as Open Access through the CCU Libraries Open Access Publishing Fund. The article was first published in the journal Bioinspiration & Biomimetics: https://doi.org/10.1088/1748-3190/acf54
Aerodynamic ground effect in fruitfly sized insect takeoff
Aerodynamic ground effect in flapping-wing insect flight is of importance to
comparative morphologies and of interest to the micro-air-vehicle (MAV)
community. Recent studies, however, show apparently contradictory results of
either some significant extra lift or power savings, or zero ground effect.
Here we present a numerical study of fruitfly sized insect takeoff with a
specific focus on the significance of leg thrust and wing kinematics.
Flapping-wing takeoff is studied using numerical modelling and high performance
computing. The aerodynamic forces are calculated using a three-dimensional
Navier--Stokes solver based on a pseudo-spectral method with volume
penalization. It is coupled with a flight dynamics solver that accounts for the
body weight, inertia and the leg thrust, while only having two degrees of
freedom: the vertical and the longitudinal horizontal displacement. The natural
voluntary takeoff of a fruitfly is considered as reference. The parameters of
the model are then varied to explore possible effects of interaction between
the flapping-wing model and the ground plane. These modified takeoffs include
cases with decreased leg thrust parameter, and/or with periodic wing
kinematics, constant body pitch angle. The results show that the ground effect
during natural voluntary takeoff is negligible. In the modified takeoffs, when
the rate of climb is slow, the difference in the aerodynamic forces due to the
interaction with the ground is up to 6%. Surprisingly, depending on the
kinematics, the difference is either positive or negative, in contrast to the
intuition based on the helicopter theory, which suggests positive excess lift.
This effect is attributed to unsteady wing-wake interactions. A similar effect
is found during hovering
On the estimation of time dependent lift of a European Starling during flapping
We study the role of unsteady lift in the context of flapping wings in birds'
flight. Both aerodynamicists and biologists attempt to address this subject,
yet it seems that the contribution of the unsteady lift still holds many open
questions. The current study deals with the estimation of unsteady aerodynamic
forces on a freely flying bird through analysis of wingbeat kinematics and near
wake flow measurements using time resolved particle image velocimetry. The
aerodynamic forces are obtained through unsteady thin airfoil theory and lift
calculation using the momentum equation for viscous flows. The unsteady lift is
comprised of circulatory and non-circulatory components. Both are presented
over wingbeat cycles. Using long sampling data, several wingbeat cycles have
been analyzed in order to cover the downstroke and upstroke phases. It appears
that the lift varies over the wingbeat cycle emphasizing its contribution to
the total lift and its role in power estimations. It is suggested that the
circulatory lift component cannot assumed to be negligible and should be
considered when estimating lift or power of birds in flapping motion
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