Aerodynamics of a Rugby Ball

2012 ◽  
Vol 79 (2) ◽  
Author(s):  
A. J. Vance ◽  
J. M. Buick ◽  
J. Livesey
Keyword(s):  
Aerodynamic Force ◽  
Angular Position ◽  
Separation Point ◽  
Aerodynamic Forces ◽  
Ball Speed ◽  
Flow Visualizations ◽  
Lift And Drag ◽  
Yaw Angle ◽  
Linear Manner ◽  
Existing Data

This paper describes the aerodynamic forces on a rugby ball traveling at speeds between 5 and 15 ms−1. This range is typical of the ball speed during passing play and a range of kicking events during a game of rugby, and complements existing data for higher velocities. At the highest speeds considered here, the lift and drag coefficients are found to be compatible with previous studies at higher velocities. In contrast to these higher speed investigations, a significant variation is observed in the aerodynamic force over the range of velocities considered. Flow visualizations are also presented, indicating how the flow pattern, which is responsible for the aerodynamic forces, changes with the yaw angle of the ball. This flow and, in particular, the position of the separation points, is examined in detail. The angular position of the separation point is found to vary in a linear manner over much of the surface of the rugby ball; however, this behavior is interrupted when the separation point is close to the ‘tip’ of the ball.

scholarly journals How oscillating aerodynamic forces explain the timbre of the hummingbird’s hum and other animals in flapping flight

eLife ◽  
2021 ◽  
Vol 10 ◽  
Author(s):  
Ben J Hightower ◽  
Patrick W A Wijnings ◽  
Rick Scholte ◽  
Rivers Ingersoll ◽  
Diana D Chin ◽  
...  
Keyword(s):  
Aerodynamic Force ◽  
Microphone Array ◽  
Flapping Wings ◽  
Acoustic Model ◽  
Acoustic Measurements ◽  
Aerodynamic Forces ◽  
Drag Forces ◽  
Radiated Power ◽  
Lift And Drag

How hummingbirds hum is not fully understood, but its biophysical origin is encoded in the acoustic nearfield. Hence, we studied six freely hovering Anna's hummingbirds, performing acoustic nearfield holography using a 2176 microphone array in vivo, while also directly measuring the 3D aerodynamic forces using a new aerodynamic force platform. We corroborate the acoustic measurements by developing an idealized acoustic model that integrates the aerodynamic forces with wing kinematics, which shows how the timbre of the hummingbird's hum arises from the oscillating lift and drag forces on each wing. Comparing birds and insects, we find that the characteristic humming timbre and radiated power of their flapping wings originates from the higher harmonics in the aerodynamic forces that support their bodyweight. Our model analysis across insects and birds shows that allometric deviation makes larger birds quieter and elongated flies louder, while also clarifying complex bioacoustic behavior.

Interferometrically Measured Aerodynamic Forces on a Vibrating Turbine Blade Group

1980 ◽  
Vol 102 (3) ◽  
pp. 638-644
Author(s):  
Z. Kovats
Keyword(s):  
Turbine Blade ◽  
Aerodynamic Force ◽  
Low Pressure ◽  
Vibration Modes ◽  
Aerodynamic Forces ◽  
Low Pressure Turbine ◽  
Pressure Distributions ◽  
Twist Mode ◽  
Lift And Drag ◽  
Measured Pressure

The instantaneous aerodynamic force and force center during a vibration cycle were determined from interferometrically measured pressure distributions around the leading blade of a low pressure turbine blade group vibrating in the tangential, axial or twist modes. The corresponding reduced frequencies were 0.0796, 0.1088 and 0.1312, and the inlet flow Mach number was 0.59 in all tests. The energy exchange per vibration cycle between the air flow and the leading blade of a group, and the lift and drag dynamic loops were determined for each of the three vibration modes. The periodic aerodynamic force coefficients were nearly sinusoidal for the axial and torsional modes but not for the tangential mode. At large negative flow incidence, the four-blade group tested is strongly unstable in the twist mode, weakly unstable in the axial mode, and strongly stable in the tangential mode. The experimental results can be used to investigate the validity of analytical predictions of the aerodynamic forces on a vibrating low pressure blade group.

scholarly journals Inter-species variation in number of bristles on forewings of tiny insects does not impact clap-and-fling aerodynamics

2020 ◽  
Author(s):  
Vishwa T. Kasoju ◽  
Mitchell P. Ford ◽  
Truc T. Ngo ◽  
Arvind Santhanakrishnan
Keyword(s):  
Drag Reduction ◽  
Aerodynamic Force ◽  
Physical Models ◽  
Species Variation ◽  
Aerodynamic Forces ◽  
Minimal Impact ◽  
Wing Span ◽  
Broad Variation ◽  
Geometric Variables ◽  
Lift And Drag

ABSTRACTFlight-capable miniature insects of body length (BL) < 2 mm typically possess wings with long bristles on the fringes. Though their flight is challenged by needing to overcome significant viscous resistance at chord-based Reynolds number (Rec) on the order of 10, these insects use clap-and-fling mechanism coupled with bristled wings for lift augmentation and drag reduction. However, inter-species variation in the number of bristles (n) and inter-bristle gap (G) to bristle diameter (D) ratio (G/D) and their effects on clap-and-fling aerodynamics remain unknown. Forewing image analyses of 16 species of thrips and 21 species of fairyflies showed that n and maximum wing span were both positively correlated with BL. We conducted aerodynamic force measurements and flow visualization on simplified physical models of bristled wing pairs that were prescribed to execute clap-and-fling kinematics at Rec=10 using a dynamically scaled robotic platform. 23 bristled wing pairs were tested to examine the isolated effects of changing dimensional (G, D, span) and non-dimensional (n, G/D) geometric variables on dimensionless lift and drag. Within biologically observed ranges of n and G/D, we found that: (a) increasing G provided more drag reduction than decreasing D; (b) changing n had minimal impact on lift generation; and (c) varying G/D produced minimal changes in aerodynamic forces. Taken together with the broad variation in n (32-161) across the species considered here, the lack of impact of changing n on lift generation suggests that tiny insects may experience reduced biological pressure to functionally optimize n for a given wing span.SUMMARY STATEMENTIntegrating morphological analysis of bristled wings seen in miniature insects with physical model experiments, we find that aerodynamic forces are unaffected across the broad biological variation in number of bristles.

Extremely Gusty Winds from a Viewpoint of Aerodynamic Force

2020 ◽  
Author(s):  
Junji Maeda ◽  
Takashi Takeuchi ◽  
Eriko Tomokiyo ◽  
Yukio Tamura
Keyword(s):  
Wind Speed ◽  
Wind Tunnel ◽  
Rise Time ◽  
Aerodynamic Force ◽  
Step Function ◽  
Object Size ◽  
Aerodynamic Forces ◽  
Wind Force ◽  
Wind Observation

To quantitatively investigate a gusty wind from the viewpoint of aerodynamic forces, a wind tunnel that can control the rise time of a step-function-like gust was devised and utilized. When the non-dimensional rise time, which is calculated using the rise time of the gusty wind, the wind speed, and the size of an object, is less than a certain value, the wind force is greater than under the corresponding steady wind. Therefore, this wind force is called the “overshoot wind force” for objects the size of orbital vehicles in an actual wind observation. The finding of the overshoot wind force requires a condition of the wind speed recording specification and depends on the object size and the gusty wind speed.

CFD study of aerodynamic performance of non-pneumatic tyre with hexagonal spokes

2021 ◽  
pp. 095440702110131
Author(s):  
Daksh Bhatia ◽  
Praneeth KR ◽  
Babu Rao Ponangi ◽  
Meghana Athadkar ◽  
Carine V Dsouza
Keyword(s):  
Comparative Study ◽  
Lift Coefficient ◽  
Aerodynamic Performance ◽  
Practical Implementation ◽  
Air Velocity ◽  
Aerodynamic Forces ◽  
Steering Angle ◽  
Camber Angle ◽  
Drag And Lift ◽  
Yaw Angle

Non-pneumatic tyres (NPT) provide a greater advantage over the pneumatic type owing to their construct which increases the reliability of the tyre operation and effectively reduces maintenance involved. Analysing the aerodynamic forces acting on a NPT becomes a crucial factor in understanding it’s suitability for practical implementation. In the present work, the aerodynamic performance of a NPT using CFD tool – SimScale® is studied. This work includes a comparative study of a pneumatic tyre, a NPT with wedge spokes and a NPT with hexagonal spokes (NPT-HS). The effect of air velocity, steering (yaw) angle and camber angle on the aerodynamic performance of the NPT-HS is evaluated using CFD. By increasing the steering angle from 0° to 15°, the lift coefficient decreases by 37% approximately at all velocities. Whereas drag coefficient initially decreases by 21% till 7.5° steering angle and then starts increasing. Increasing camber angle from 0° to 1.5°, both drag and lift coefficients goes on decreasing by approximately 7% and 27% respectively.

Runway debris impact threat maps for transport aircraft

2014 ◽  
Vol 118 (1201) ◽  
pp. 229-266 ◽  
Author(s):  
S. N. Nguyen ◽  
E. S. Greenhalgh ◽  
J. M. R. Graham ◽  
A. Francis ◽  
R. Olsson
Keyword(s):  
Finite Element ◽  
Finite Element Modelling ◽  
Impact Damage ◽  
Landing Gear ◽  
Aerodynamic Forces ◽  
Element Modelling ◽  
Transport Aircraft ◽  
Lift And Drag ◽  
The Impact ◽  
Debris Impact

AbstractLarge transport aircraft are particularly susceptible to impact damage from runway debris thrown up by the landing gear. A methodology was developed to predict the trajectories of stones lofted by the nose wheel and subjected to aerodynamic forces due to the wake behind the nose landing gear and beneath the aircraft. In conjunction with finite element modelling of the stone/ground/tyre contact mechanics, an analytical model was used to perform a stochastic prediction of the trajectories of runway stones to generate impact threat maps which showed the relative likelihood of stones impinging upon various areas on the underside of a C-130 Hercules. The impact envelopes for the C-130 extended three to eighteen metres behind the nose wheel and two metres either side of the centre of the aircraft. The impact threat maps were especially sensitive to the values of the coefficients of lift and drag acting on the stone during its flight.

scholarly journals DeepPilot: A CNN for Autonomous Drone Racing

Sensors ◽  
2020 ◽  
Vol 20 (16) ◽  
pp. 4524
Author(s):  
Leticia Oyuki Rojas-Perez ◽  
Jose Martinez-Carranza
Keyword(s):  
Deep Learning ◽  
Flight Control ◽  
Rotational Speed ◽  
Angular Position ◽  
Body Frame ◽  
Mosaic Image ◽  
Vertical Speed ◽  
Translation Motion ◽  
Yaw Angle ◽  
Detection And Localization

Autonomous Drone Racing (ADR) was first proposed in IROS 2016. It called for the development of an autonomous drone capable of beating a human in a drone race. After almost five years, several teams have proposed different solutions with a common pipeline: gate detection; drone localization; and stable flight control. Recently, Deep Learning (DL) has been used for gate detection and localization of the drone regarding the gate. However, recent competitions such as the Game of Drones, held at NeurIPS 2019, called for solutions where DL played a more significant role. Motivated by the latter, in this work, we propose a CNN approach called DeepPilot that takes camera images as input and predicts flight commands as output. These flight commands represent: the angular position of the drone’s body frame in the roll and pitch angles, thus producing translation motion in those angles; rotational speed in the yaw angle; and vertical speed referred as altitude h. Values for these 4 flight commands, predicted by DeepPilot, are passed to the drone’s inner controller, thus enabling the drone to navigate autonomously through the gates in the racetrack. For this, we assume that the next gate becomes visible immediately after the current gate has been crossed. We present evaluations in simulated racetrack environments where DeepPilot is run several times successfully to prove repeatability. In average, DeepPilot runs at 25 frames per second (fps). We also present a thorough evaluation of what we called a temporal approach, which consists of creating a mosaic image, with consecutive camera frames, that is passed as input to the DeepPilot. We argue that this helps to learn the drone’s motion trend regarding the gate, thus acting as a local memory that leverages the prediction of the flight commands. Our results indicate that this purely DL-based artificial pilot is feasible to be used for the ADR challenge.

Aerodynamic effects of bio-inspired corrugated wings on gliding and hovering performances

2020 ◽  
pp. 095440622091799
Author(s):  
Haibin Xuan ◽  
Jun Hu ◽  
Yong Yu ◽  
Jiaolong Zhang
Keyword(s):  
Inclination Angle ◽  
Fluid Dynamic ◽  
Angle Of Attack ◽  
Aerodynamic Forces ◽  
Limited Effect ◽  
Gliding Flight ◽  
Significant Difference ◽  
Inclination Angles ◽  
Underlying Mechanisms ◽  
Lift And Drag

Recently, numerous studies have been conducted to clarify the effects of corrugation wing on aerodynamic performances. The effects of the corrugation patterns and inclination angles were investigated using computational fluid dynamic method in gliding and hovering flight at Reynolds numbers of order 104. The instantaneous aerodynamic forces and the vorticity field around the wing models were provided to research the underlying mechanisms of aerodynamic effects of corrugated wing models. The findings can be concluded as follows: (1) the corrugation patterns have different effects on aerodynamic performance. The effect of noncamber corrugated wing is to decrease the lift and increase drag compared with a flat-plate when the angle of attack is less than 25° during gliding flight. The corrugated wing with a camber (corrug-2) after the valleys enhances the aerodynamic forces when angle of attack is higher than 35°. The valley inclination angle has limited effect on aerodynamic forces in gliding flight. (2) The lift forces of different corrugation patterns show significantly asymmetric during the upstroke and downstroke. The main reason leads to this phenomenon is the case that two sides of the corrugated wings are not symmetric around the pitching axis. The corrugated wing with only two valleys (corrug-1) changes the lift and drag very slightly. Corrug-2 produces larger peak during downstroke and smaller peak during upstroke. The increase in the inclination angle has limited effect on the aerodynamic forces. The possible reason for these small aerodynamic effects might be that the corrugated wings are smoothed by small vortices trapped in valleys. The main reason for the significant difference between plate and corrug-2 is that the recirculating vortices trapped in the saddle and hump reduce the pressure above the wing surface.

Bifurcation Analysis of Parametrically Excited Moving String With Aerodynamic Forces

2012 ◽  
Author(s):  
Changzhao Qian ◽  
Changping Chen ◽  
Liming Dai
Keyword(s):  
Bifurcation Analysis ◽  
Parametric Analysis ◽  
Aerodynamic Force ◽  
Equation Of Motion ◽  
Stable Region ◽  
Second Law ◽  
Bifurcation Equation ◽  
Aerodynamic Forces ◽  
Average Equation ◽  
Prototypical Model

Considering the large deformation of the string, A prototypical model of a elastic moving string with aerodynamic forces is studied. The equation of motion is obtained by Newton’s second law. Then the Perturbation method is used to obtain the average equation and bifurcation equation. Based on the average equation, the stable region of this system is discussed. Based on the bifurcation equation, the multivalued property of response amplitude is studied. At last, the flutter effects of aerodynamic force are discussed by the parametric analysis.

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