scholarly journals Flight kinematics of the barn swallow (Hirundo rustica) over a wide range of speeds in a wind tunnel

2001 ◽  
Vol 204 (15) ◽  
pp. 2741-2750 ◽  
Author(s):  
Kirsty J. Park ◽  
Mikael Rosén ◽  
Anders Hedenström
Keyword(s):  
Wind Tunnel ◽  
Tilt Angle ◽  
Angle Of Attack ◽  
The Body ◽  
Hirundo Rustica ◽  
Body Tilt ◽  
High Plasticity ◽  
Wingbeat Frequency ◽  
High Speeds ◽  
Wide Range

SUMMARYTwo barn swallows (Hirundo rustica) flying in the Lund wind tunnel were filmed using synchronised high-speed cameras to obtain posterior, ventral and lateral views of the birds in horizontal flapping flight. We investigated wingbeat kinematics, body tilt angle, tail spread and angle of attack at speeds of 4–14ms−1. Wingbeat frequency showed a clear U-shaped relationship with air speed with minima at 8.9ms−1(bird 1) and 8.7ms−1 (bird 2). A method previously used by other authors of estimating the body drag coefficient (CD,par) by obtaining agreement between the calculated minimum power (Vmin) and the observed minimum wingbeat frequency does not appear to be valid in this species, possibly due to upstroke pauses that occur at intermediate and high speeds, causing the apparent wingbeat frequency to be lower. These upstroke pauses represent flap-gliding, which is possibly a way of adjusting the force generated to the requirements at medium and high speeds, similar to the flap-bound mode of flight in other species. Body tilt angle, tail spread and angle of attack all increase with decreasing speed, thereby providing an additional lift surface and suggesting an important aerodynamic function for the tail at low speeds in forward flight. Results from this study indicate the high plasticity in the wingbeat kinematics and use of the tail that birds have available to them in order to adjust the lift and power output required for flight.

scholarly journals Wingbeat frequency and the body drag anomaly: wind-tunnel observations on a thrush nightingale (Luscinia luscinia) and a teal (Anas crecca)

1996 ◽  
Vol 199 (12) ◽  
pp. 2757-2765 ◽  
Author(s):  
C J Pennycuick ◽  
M Klaassen ◽  
A Kvist ◽  
Å Lindström
Keyword(s):  
Wind Tunnel ◽  
The Body ◽  
Wingbeat Frequency ◽  
Cross Sectional ◽  
Number Range ◽  
Drag Coefficients ◽  
Anas Crecca ◽  
Body Drag ◽  
Air Speed ◽  
Thrush Nightingale

A teal (Anas crecca) and a thrush nightingale (Luscinia luscinia) were trained to fly in the Lund wind tunnel for periods of up to 3 and 16 h respectively. Both birds flew in steady flapping flight, with such regularity that their wingbeat frequencies could be determined by viewing them through a shutter stroboscope. When flying at a constant air speed, the teal's wingbeat frequency varied with the 0.364 power of the body mass and the thrush nightingale's varied with the 0.430 power. Both exponents differed from zero, but neither differed from the predicted value (0.5) at the 1 % level of significance. The teal continued to flap steadily as the tunnel tilt angle was varied from -1 ° (climb) to +6 ° (descent), while the wingbeat frequency declined progressively by about 11 %. In both birds, the plot of wingbeat frequency against air speed in level flight was U-shaped, with small but statistically significant curvature. We identified the minima of these curves with the minimum power speed (Vmp) and found that the values predicted for Vmp, using previously published default values for the required variables, were only about two-thirds of the observed minimum-frequency speeds. The discrepancy could be resolved if the body drag coefficients (CDb) of both birds were near 0.08, rather than near 0.40 as previously assumed. The previously published high values for body drag coefficients were derived from wind-tunnel measurements on frozen bird bodies, from which the wings had been removed, and had long been regarded as anomalous, as values below 0.01 are given in the engineering literature for streamlined bodies. We suggest that birds of any size that have well-streamlined bodies can achieve minimum body drag coefficients of around 0.05 if the feet can be fully retracted under the flank feathers. In such birds, field observations of flight speeds may need to be reinterpreted in the light of higher estimates of Vmp. Estimates of the effective lift:drag ratio and range can also be revised upwards. Birds that have large feet or trailing legs may have higher body drag coefficients. The original estimates of around CDb=0.4 could be correct for species, such as pelicans and large herons, that also have prominent heads. We see no evidence for any progressive reduction of body drag coefficient in the Reynolds number range covered by our experiments, that is 21 600­215 000 on the basis of body cross-sectional diameter.

scholarly journals Gait Transition from Pacing by a Quadrupedal Simulated Model and Robot with Phase Modulation by Vestibular Feedback

Robotics ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 3
Author(s):  
Takahiro Fukui ◽  
Souichiro Matsukawa ◽  
Yasushi Habu ◽  
Yasuhiro Fukuoka
Keyword(s):  
Phase Modulation ◽  
Control Method ◽  
Pattern Generator ◽  
The Body ◽  
Body Tilt ◽  
Effective Control ◽  
Pd Controller ◽  
Gait Transition ◽  
Quadruped Robots ◽  
High Speeds

We propose a method to achieve autonomous gait transition according to speed for a quadruped robot pacing at medium speeds. We verified its effectiveness through experiments with the simulation model and the robot we developed. In our proposed method, a central pattern generator (CPG) is applied to each leg. Each leg is controlled by a PD controller based on output from the CPG. The four CPGs are coupled, and a hard-wired CPG network generates a pace pattern by default. In addition, we feed the body tilt back to the CPGs in order to adapt to the body oscillation that changes according to the speed. As a result, our model and robot achieve stable changes in speed while autonomously generating a walk at low speeds and a rotary gallop at high speeds, despite the fact that the walk and rotary gallop are not preprogramed. The body tilt angle feedback is the only factor involved in the autonomous generation of gaits, so it can be easily used for various quadruped robots. Therefore, it is expected that the proposed method will be an effective control method for quadruped robots.

Experimental investigation of ground effects on aerodynamics of sinusoidal leading-edge wings

2020 ◽  
pp. 095440622097542
Author(s):  
AA Mehraban ◽  
MH Djavareshkian
Keyword(s):  
Experimental Investigation ◽  
Reynolds Number ◽  
Wind Tunnel ◽  
Research Study ◽  
Lift Coefficient ◽  
Angle Of Attack ◽  
Leading Edge ◽  
Aerodynamic Performance ◽  
Wide Range ◽  
Ground Effects

Sinusoidal leading-edge wings have attracted many considerations since they can delay the stall and enhance the maneuverability. The main contribution of this research study is to experimentally investigate effects of ground on aerodynamic performance of sinusoidal leading-edge wings. To this end, 6 tubercled wings with different amplitudes and wavelengths are fabricated and compared with the baseline wing which has smooth leading-edge. Proposed wings are tested in different distances from the ground in a wind tunnel lab for a wide range of angle of attack from 0° to 36° and low Reynolds number of 45,000. Results indicated that lift coefficient is improved when wings get close to the ground. Furthermore, increment of protuberance amplitude in the vicinity of the ground could efficiently prevent stalling particularly for shorter wavelength.

scholarly journals Fluid–structure interaction of a square cylinder at different angles of attack

2014 ◽  
Vol 747 ◽  
pp. 688-721 ◽  
Author(s):  
Jisheng Zhao ◽  
Justin S. Leontini ◽  
David Lo Jacono ◽  
John Sheridan
Keyword(s):  
Vortex Shedding ◽  
Oscillation Frequency ◽  
Angle Of Attack ◽  
Flow Speed ◽  
The Body ◽  
Direct Result ◽  
Square Cylinder ◽  
Amplitude Response ◽  
Integer Multiple ◽  
Wide Range

AbstractThis study investigates the free transverse flow-induced vibration (FIV) of an elastically mounted low-mass-ratio square cylinder in a free stream, at three different incidence angles: ${{\alpha }}=0^\circ $, $20^\circ $ and $45^\circ $. This geometric setup presents a body with an angle of attack, sharp corners and some afterbody, and therefore is a generic body that can be used to investigate a wide range of FIV phenomena. A recent study by Nemes et al. (J. Fluid Mech., vol. 710, 2012, pp. 102–130) provided a broad overview of the flow regimes present as a function of both the angle of attack ${{\alpha }}$ and reduced flow velocity ${U^{*}}$. Here, the focus is on the three aforementioned representative angles of attack: ${{\alpha }}=0^\circ $, where the FIV is dominated by transverse galloping; ${{\alpha }}=45^\circ $, where the FIV is dominated by vortex-induced vibration (VIV); and an intermediate value of ${{\alpha }}=20^\circ $, where the underlying FIV phenomenon has previously been difficult to determine. For the ${{\alpha }}=0^\circ $ case, the amplitude of oscillation increases linearly with the flow speed except for a series of regimes that occur when the vortex shedding frequency is in the vicinity of an odd-integer multiple of the galloping oscillation frequency, and the vortex shedding synchronizes to this multiple of the oscillation frequency. It is shown that only odd-integer multiple synchronizations should occur. These synchronizations explain the ‘kinks’ in the galloping amplitude response for light bodies first observed by Bearman et al. (J. Fluids Struct., vol. 1, 1987, pp. 19–34). For the ${{\alpha }}=45^\circ $ case, the VIV response consists of a number of subtle, but distinctly different regimes, with five regimes of high-amplitude oscillations, compared to two found in the classic VIV studies of a circular cylinder. For the intermediate ${{\alpha }}=20^\circ $ case, a typical VIV ‘upper branch’ occurs followed by a ‘higher branch’ of very large-amplitude response. The higher branch is caused by a subharmonic synchronization between the vortex shedding and the body oscillation frequency, where two cycles of vortex shedding occur over one cycle of oscillation. It appears that this subharmonic synchronization is a direct result of the asymmetric body. Overall, the FIV of the square cylinder is shown to be very rich, with a number of distinct regimes, controlled by both ${{\alpha }}$ and ${U^{*}}$. Importantly, ${{\alpha }}$ controls the underlying FIV phenomenon, as well as controlling the types of possible synchronization between the oscillation and vortex shedding.

Response of vestibular neurons to head rotations in vertical planes. II. Response to neck stimulation and vestibular-neck interaction

1988 ◽  
Vol 60 (5) ◽  
pp. 1765-1778 ◽  
Author(s):  
J. Kasper ◽  
R. H. Schor ◽  
V. J. Wilson
Keyword(s):  
Head Rotation ◽  
The Body ◽  
Head Movements ◽  
Body Tilt ◽  
Whole Body ◽  
Frequency Range ◽  
Vestibular Input ◽  
Response Dynamics ◽  
Neck Input ◽  
Wide Range

1. We have studied the responses of neurons in the lateral and descending vestibular nuclei of decerebrate cats to stimulation of neck receptors, produced by rotating the body in vertical planes with the head stationary. The responses to such neck stimulation were compared with the responses to vestibular stimulation produced by whole-body tilt, described in the preceding paper. 2. After determining the optimal vertical plane of neck rotation (response vector orientation), the dynamics of the neck response were studied over a frequency range of 0.02-1 Hz. The majority of the neurons were excited by neck rotations that brought the chin toward the ipsilateral side; most neurons responded better to roll than to pitch rotations. The typical neck response showed a low-frequency phase lead of 30 degrees, increasing to 60 degrees at higher frequencies, and a gain that increased about threefold per decade. 3. Neck input was found in about one-half of the vestibular-responsive neurons tested with vertical rotations. The presence of a neck response was correlated with the predominant vestibular input to these neurons; neck input was most prevalent on neurons with vestibular vector orientations near roll and receiving convergent vestibular input, either input from both ipsilateral vertical semicircular canals, or from canals plus the otolith organs. 4. Neurons with both vestibular and neck responses tend to have the respective orientation vectors pointing in opposite directions, i.e., a head tilt that produces an excitatory vestibular response would produce an inhibitory neck response. In addition, the gain components of these responses were similar. These results suggest that during head movements on a stationary body, these opposing neck and vestibular inputs will cancel each other. 5. Cancellation was observed in 12 out of 27 neurons tested with head rotation in the mid-frequency range. For most of the remaining neurons, the response to such a combined stimulus was greatly attenuated: the vestibular and neck interaction was largely antagonistic. 6. Neck response dynamics were similar to those of the vestibular input in many neurons, permitting cancellation to take place over a wide range of stimulus frequencies. Another pattern of interaction, observed in some neurons with canal input, produced responses to head rotation that had a relatively constant gain and remained in phase with position over the entire frequency range; such neurons possibly code head position in space.

scholarly journals Aerodynamic analysis of aircraft model using indigenously developed wind tunnel facility

2021 ◽  
Vol 1206 (1) ◽  
pp. 012013
Author(s):  
D Makhija ◽  
S V Jain ◽  
A M Achari ◽  
K Ghosh
Keyword(s):  
Wind Tunnel ◽  
Lift Force ◽  
Lift Coefficient ◽  
Pressure Coefficient ◽  
Angle Of Attack ◽  
Open Circuit ◽  
Force Balance ◽  
Number Range ◽  
Aircraft Model ◽  
Wide Range

Abstract This paper presents a design of force balance setup that can measure lift force acting on the aircraft model. The setup was developed indigenously and installed in an open circuit low-speed wind tunnel. It mainly consists of two components viz. a traverse mechanism that can hold the model in the test section at different angles of attack and air speeds and a supporting frame to hold the traverse mechanism over it. The spring balances are used to obtain lift force readings at different angles and air speeds. The experimental and numerical investigations were done in the wide range of Reynolds number (range: 0.55 to 1.12 lakh) and angle of attack (range: -6° to 20°). The results are presented in terms of pressure contours, velocity contours, pressure coefficient and lift coefficient. From the experiments it was found that value of lift coefficient increases with angle of attack and stalling occurs at 18° for all the air speeds. However, in the numerical results the stalling was observed little earlier than 18° angle of attack. The experimental results were compared with CFD results and an average relative error of 18% was observed which may be due to assumption of 2-D airfoil in CFD analysis.

The metabolic cost of flight in unrestrained birds

1978 ◽  
Vol 75 (1) ◽  
pp. 223-229 ◽  
Author(s):  
J. R. Torre-Bueno ◽  
J. Larochelle
Keyword(s):  
Carbon Dioxide ◽  
Metabolic Rate ◽  
Metabolic Cost ◽  
Large Change ◽  
Carbon Dioxide Production ◽  
The Body ◽  
Wingbeat Frequency ◽  
Bird Flight ◽  
Body Attitude ◽  
High Speeds

Oxygen consumption and carbon dioxide production were measured during flight in unrestrained starlings by a new method. Mean RQ after the first 30 min of flight was 0.69 +/− 0.08 (+/− S.D.). Mean rate of carbon dioxide production was 19.7 +/− 2.2 ml CO2/min, which corresponds to a metabolic rate of 8.9 +/− 1 W. Metabolic rate during flight did not change significantly over a range of air speeds from 8 to 18 m/s and birds would not fly at speeds outside of this range. Current theories of bird flight predict a large change in metabolic rate over the same range of speeds. Wingbeat frequency was constant at 12 +/− 0.5 Hz. Wingbeat amplitude reached a minimum at a speed of 14 m/s and increased at both higher and lower speeds. Angle between the body and horizontal was least at high speeds and increased at low speeds. As existing theories do not take into account the change of drag resulting from changes in body attitude, this may be a cause of the discrepancies between theory and observation.

Flexibility in flight behaviour of barn swallows (Hirundo rustica) and house martins (Delichon urbica) tested in a wind tunnel

2001 ◽  
Vol 204 (8) ◽  
pp. 1473-1484 ◽  
Author(s):  
L. Bruderer ◽  
F. Liechti ◽  
D. Bilo
Keyword(s):  
Wind Tunnel ◽  
Hirundo Rustica ◽  
Wingbeat Frequency ◽  
Flight Behaviour ◽  
Delichon Urbica ◽  
Gliding Flight ◽  
Mechanical Power Output ◽  
Intermittent Flight ◽  
Barn Swallows ◽  
Air Speed

The flight behaviour of barn swallows (Hirundo rustica) and house martins (Delichon urbica) was tested in a wind tunnel at 15 combinations of flight angles and speeds. In contrast to that of most other small passerines, the intermittent flight of hirundines rarely consists of regular patterns of flapping and rest phases. To vary mechanical power output, both species used intermittent flight, controlling the number of single, pulse-like wingbeats per unit time. House martins in descent tended to concentrate their wingbeats into bursts and performed true gliding flight during rest phases. Barn swallows mainly performed partial bounds during brief interruptions of upstrokes, which they progressively prolonged with decreasing flight angle. Thus, identification of distinct flapping phases to calculate wingbeat frequencies was not feasible. Instead, an effective wingbeat frequency for flight intervals of 20 s, including partial bounds, was introduced. The effective wingbeat frequencies of house martins (N=3) ranged from 2 to 10.5 s(−)(1), those of barn swallows (N=4) from 2.5 to 8.5 s(−)(1). In both hirundine species, effective wingbeat frequency was found to decrease almost linearly with decreasing flight angle. With changes in air speed, wingbeat frequency varied according to a U-shaped curve, suggesting a minimum power speed of roughly 9 m s(−)(1). The duration of the down- and upstrokes varied systematically depending on flight angle and air speed.

Creating the Wind

2020 ◽  
Vol 2 (4) ◽  
pp. 14-31
Author(s):  
Élodie Dupey García
Keyword(s):  
Indigenous Communities ◽  
The Body ◽  
Historical Sources ◽  
Natural Behavior ◽  
Sensory Experiences ◽  
Identity And Agency ◽  
Wide Range ◽  
Late Postclassic ◽  
Comparative Examination ◽  
Meteorological Phenomenon

This article explores how the Nahua of late Postclassic Mesoamerica (1200–1521 CE) created living and material embodiments of their wind god constructed on the basis of sensory experiences that shaped their conception of this divinized meteorological phenomenon. In this process, they employed chromatic and design devices, based on a wide range of natural elements, to add several layers of meaning to the human, painted, and sculpted supports dressed in the god’s insignia. Through a comparative examination of pre-Columbian visual production—especially codices and sculptures—historical sources mainly written in Nahuatl during the viceregal period, and ethnographic data on indigenous communities in modern Mexico, my analysis targets the body paint and shell jewelry of the anthropomorphic “images” of the wind god, along with the Feathered Serpent and the monkey-inspired embodiments of the deity. This study identifies the centrality of other human senses beyond sight in the conception of the wind god and the making of its earthly manifestations. Constructing these deity “images” was tantamount to creating the wind because they were intended to be visual replicas of the wind’s natural behavior. At the same time, they referred to the identity and agency of the wind god in myths and rituals.

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