scholarly journals On the autorotation of animal wings

2017 ◽  
Vol 14 (126) ◽  
pp. 20160870 ◽  
Author(s):  
Victor Manuel Ortega-Jimenez ◽  
Antonio Martín-Alcántara ◽  
Ramon Fernandez-Feria ◽  
Robert Dudley
Keyword(s):  
Scaling Law ◽  
Practical Method ◽  
Aerodynamic Performance ◽  
Centre Of Mass ◽  
Aerodynamic Forces ◽  
Partial Removal ◽  
Wing Base ◽  
Improved Performance ◽  
Outer Primary ◽  
Wing Aspect Ratio

Botanical samaras spin about their centre of mass and create vertical aerodynamic forces which slow their rate of descent. Descending autorotation of animal wings, however, has never been documented. We report here that isolated wings from Anna's hummingbirds, and also from 10 species of insects, can stably autorotate and achieve descent speeds and aerodynamic performance comparable to those of samaras. A hummingbird wing loaded at its base with the equivalent of 50% of the bird's body mass descended only twice as fast as an unloaded wing, and rotated at frequencies similar to those of the wings in flapping flight. We found that even entire dead insects could stably autorotate depending on their wing postures. Feather removal trials showed no effect on descent velocity when the secondary feathers were removed from hummingbird wings. By contrast, partial removal of wing primaries substantially improved performance, except when only the outer primary was present. A scaling law for the aerodynamic performance of autorotating wings is well supported if the wing aspect ratio and the relative position of the spinning axis from the wing base are included. Autorotation is a useful and practical method that can be used to explore the aerodynamics of wing design.

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.

scholarly journals Effect of Single-Row and Double-Row Passive Vortex Generators on the Deep Dynamic Stall of a Wind Turbine Airfoil

Energies ◽  
2020 ◽  
Vol 13 (10) ◽  
pp. 2535
Author(s):  
Chengyong Zhu ◽  
Tongguang Wang ◽  
Jie Chen ◽  
Wei Zhong
Keyword(s):  
Wind Turbine ◽  
Flow Separation ◽  
Aerodynamic Performance ◽  
Vortex Generators ◽  
Dynamic Stall ◽  
Aerodynamic Forces ◽  
Double Row ◽  
Single Row ◽  
Maximum Angle ◽  
Wind Turbine Airfoil

Passive vortex generators (VGs) have been widely applied on wind turbines to boost the aerodynamic performance. Although VGs can delay the onset of static stall, the effect of VGs on dynamic stall is still incompletely understood. Therefore, this paper aims at investigating the deep dynamic stall of NREL S809 airfoil controlled by single-row and double-row VGs. The URANS method with VGs fully resolved is used to simulate the unsteady airfoil flow. Firstly, both single-row and double-row VGs effectively suppress the flow separation and reduce the fluctuations in aerodynamic forces when the airfoil pitches up. The maximum lift coefficient is therefore increased beyond 40%, and the onset of deep dynamic stall is also delayed. This suggests that deep dynamic-stall behaviors can be properly controlled by VGs. Secondly, there is a great difference in aerodynamic performance between single-row and double-row VGs when the airfoil pitches down. Single-row VGs severely reduce the aerodynamic pitch damping by 64%, thereby undermining the torsional aeroelastic stability of airfoil. Double-row VGs quickly restore the decreased aerodynamic efficiency near the maximum angle of attack, and also significantly accelerate the flow reattachment. The second-row VGs can help the near-wall flow to withstand the adverse pressure gradient and then suppress the trailing-edge flow separation, particularly during the downstroke process. Generally, double-row VGs are better than single-row VGs concerning controlling deep dynamic stall. This work also gives a performance assessment of VGs in controlling the highly unsteady aerodynamic forces of a wind turbine airfoil.

scholarly journals Complexity Analysis on the Aerodynamic Performance of the Mega High-Speed Train Caused by the Wind Barrier on the Embankment

Complexity ◽  
2018 ◽  
Vol 2018 ◽  
pp. 1-17
Author(s):  
He-xuan Hu ◽  
Wan-xin Lei ◽  
Ye Zhang
Keyword(s):  
Negative Pressure ◽  
High Speed ◽  
Complexity Analysis ◽  
Aerodynamic Force ◽  
Pressure Change ◽  
Aerodynamic Performance ◽  
Head Wave ◽  
High Speed Train ◽  
Aerodynamic Forces ◽  
Negative Wave

With the world development of high-speed railways and increasing speeds, aerodynamic forces and moments acting on trains have been increased further, making trains stay at a “floated” state. Under a strong crosswind, the aerodynamic performance of a train on the embankment is greatly deteriorated; lift force and horizontal force borne by trains will be increased quickly; trains may suffer derailing or overturning more easily compared with the flat ground; train derailing will take place when the case is serious. All of these phenomena have brought risks to people’s life and properties. Hence, the paper establishes an aerodynamic model about a high-speed train passing an air barrier, computes aerodynamic forces and moments, and analyzes pulsating pressures on the train surface as well as those of unsteady flow fields around the train. Computational results indicate that when the train passed the embankment air barrier, the head wave of air pressure full wave is more than the tail wave; the absolute value of negative wave is more than that of the positive wave, which is more obvious in the head train. When the train is passing the air barrier, pressure pulsation values at head train points are more than those at other points, while pressure changes most violently at the train bottom, and pressure values close to the air barrier are more than those points far from the air barrier. Pressure values at the cross section 1 were larger than those of other points. Pressure values at measurement points of the tail train ranked the second place, with the maximum negative pressure of 1253 Pa. Pressure change amplitudes and maximum negative pressure on the train surface are increased quickly, while pressure peak values on the high-speed train surface are in direct ratio to the running speed. With the increased speed of the high-speed train, when it is running in the embankment air barrier, the aerodynamic force and moment borne by each train body are increased sharply, while the head train suffers the most obvious influences of aerodynamic effects.

scholarly journals An Experimental Analysis on the Effects of Stagger on the Aerodynamic Forces of Tandem Wings

AVIA ◽  
2021 ◽  
Vol 2 (2) ◽  
Author(s):  
Y Parlindungan ◽  
S Tobing
Keyword(s):  
Experimental Analysis ◽  
Numerical Study ◽  
Lift Coefficient ◽  
Angle Of Attack ◽  
Aerodynamic Performance ◽  
Open Loop ◽  
Aerodynamic Forces ◽  
Subsonic Wind Tunnel ◽  
Lift And Drag ◽  
Naca 0012

This study is inspired by the flapping motion of natural flyers: insects. Many insects have two pairs of wings referred as tandem wings. Literature review indicates that the effects of tandem wing are influenced by parameters such as stagger (the stream-wise distance between the aerodynamic center of the front and the rear airfoil), angle-of-attack and flow velocity. As a first stage, this study focuses on the effects of stagger (St) on the aerodynamic performance of tandem wings. A recent numerical study of stagger on tandem airfoils in turbulent flow (Re = 6000000) concluded that a larger stagger resulted in a decrease in lift force, and an increase in drag force. However, for laminar flow (Re = 2000), increasing the stagger was not found to be detrimental for aerodynamic performance. Another work also revealed that the maximum lift coefficient for a tandem configuration decreased with increasing stagger. The focus of this study is to perform an experimental analysis of tandem two-dimensional (2D) NACA 0012 airfoils. The two airfoils are set at the same angle-of-attack of 0° to 15° with 5° interval and three variations of stagger: 1c, 1.5c and 2c. The experiments are conducted using an open-loop-subsonic wind tunnel at a Reynolds number of 170000. The effects of St on the aerodynamic forces (lift and drag) are analyzed

Aerodynamic Performance of Offwind Sails Attached to Sprits

2001 ◽  
Author(s):  
Robert Ranzenbach ◽  
Jim Teeters
Keyword(s):  
Aerodynamic Performance ◽  
Performance Potential ◽  
Prediction Program ◽  
Aerodynamic Modeling ◽  
Specific Goal ◽  
Velocity Prediction ◽  
Size Type ◽  
Improved Performance ◽  
Pole Configuration ◽  
International Measurement

The primary purpose of this offwind sail investigation was to better understand the relative performance of symmetric spinnakers flown from conventional poles and asymmetric spinnakers flown from conventional poles or sprits, i.e. poles restricted to the centerline. The specific goal was to improve the aerodynamic modeling of offwind sails used in the International Measurement System (IMS) handicapping formula to address perceived inequities in their performance potential, particularly when running at very deep angles. Running style offwind sails of varying size, type, and pole configuration were evaluated over appropriate ranges of angle of attack and trim settings. Improved performance coefficients were developed from this data for inclusion into the 2001 IMS velocity prediction program.

II. The angular motion of a freely falling rocket

1964 ◽  
Vol 279 (1379) ◽  
pp. 523-533
Keyword(s):  
Angular Velocity ◽  
Unit Length ◽  
Free Fall ◽  
Axisymmetric Body ◽  
Rigid Bodies ◽  
Angular Motion ◽  
Time Interval ◽  
Angular Momentum Vector ◽  
Centre Of Mass ◽  
Aerodynamic Forces

The motion of a rocket with its propellant exhausted and above the heights where aerodynamic forces can be used to control its motion, can be considered as that of a rigid body in free flight, subjected to small perturbations by weak aerodynamic forces. This permits the separate consideration of the motion of the centre of mass of the rocket along an approximately ‘free fall’ trajectory and the rotation of the rocket about its centre of mass. The rotational motion of free rigid bodies is well known and may be readily visualized by means of Poinsot’s construction (Corben & Stehle 1960). This analysis may be applied to the motion of a rocket with an accuracy which depends on the smallness of the residual aerodynamic forces and the time interval over which the ‘free fall’ approximation is applied. The Skylark rocket vehicle is a long axisymmetric body of approximately uniform mass per unit length. The momental ellipsoid of such a body is a long ellipsoid of revolution with its major axis along the spin axis of the rocket. In this case, the angular motion will consist only of roll and regular precession. In the early stages of the flight the rocket is given some spin motion by aero­dynamic forces on the fins. The angle between the geometrical axis of the rocket and the angular momentum vector is small and can change only slowly because of the aerodynamic forces which are important during the initial stages of the flight. The rate of precession of the rocket axis is much smaller than the rate of spin. In these circumstances, the angular motion will be as shown in figure 11 and can be regarded as roll about the vehicle axis OV with angular velocity ω and precession of this axis about an invariant direction OC with angular velocity Ω. The semi-angle, COV = ρ , of the precession cone is given by cos p = I L / I T ω / Ω , where I L and I T are the moments of inertia about longitudinal and transverse axes passing through the centre of mass.

Design of a Bio-Inspired Spherical Four-Bar Mechanism for Flapping-Wing Micro Air-Vehicle Applications

2008 ◽  
Author(s):  
Matt McDonald ◽  
Sunil K. Agrawal
Keyword(s):  
Three Dimensional ◽  
Micro Air Vehicles ◽  
Aerodynamic Performance ◽  
Flapping Wing ◽  
Micro Air Vehicle ◽  
Aerodynamic Forces ◽  
Flapping Motion ◽  
Wing Motion ◽  
Air Vehicle ◽  
Flapping Mechanism

Design of flapping-wing micro air-vehicles presents many engineering challenges. As observed by biologists, insects and birds exhibit complex three-dimensional wing motions. It is believed that these unique patterns of wing motion create favorable aerodynamic forces that enable these species to fly forward, hover, and execute complex motions. From the perspective of micro air-vehicle applications, extremely lightweight designs that accomplish these motions of the wing, using just a single, or a few actuators, are preferable. This paper presents a method to design a spherical four-bar flapping mechanism that approximates a given spatial flapping motion of a wing, considered to have favorable aerodynamics. A spherical flapping mechanism was then constructed and its aerodynamic performance was compared to the original spatially moving wing using an instrumented robotic flapper with force sensors.

scholarly journals Span efficiency in hawkmoths

2013 ◽  
Vol 10 (84) ◽  
pp. 20130099 ◽  
Author(s):  
Per Henningsson ◽  
Richard J. Bomphrey
Keyword(s):  
Aerodynamic Performance ◽  
Aerodynamic Forces ◽  
Time Resolved ◽  
Flight Muscles ◽  
Induced Flow ◽  
Instantaneous Values ◽  
Advance Ratio ◽  
Spatio Temporal ◽  
Animal Flight ◽  
Suitable Approximation

Flight in animals is the result of aerodynamic forces generated as flight muscles drive the wings through air. Aerial performance is therefore limited by the efficiency with which momentum is imparted to the air, a property that can be measured using modern techniques. We measured the induced flow fields around six hawkmoth species flying tethered in a wind tunnel to assess span efficiency, e i , and from these measurements, determined the morphological and kinematic characters that predict efficient flight. The species were selected to represent a range in wingspan from 40 to 110 mm (2.75 times) and in mass from 0.2 to 1.5 g (7.5 times) but they were similar in their overall shape and their ecology. From high spatio-temporal resolution quantitative wake images, we extracted time-resolved downwash distributions behind the hawkmoths, calculating instantaneous values of e i throughout the wingbeat cycle as well as multi-wingbeat averages. Span efficiency correlated positively with normalized lift and negatively with advance ratio. Average span efficiencies for the moths ranged from 0.31 to 0.60 showing that the standard generic value of 0.83 used in previous studies of animal flight is not a suitable approximation of aerodynamic performance in insects.

A Multi-Point Approach to Airfoil Shape Optimization

2012 ◽  
Vol 591-593 ◽  
pp. 59-62
Author(s):  
Kai Huang ◽  
Zhi Jun Meng ◽  
Jun Huang
Keyword(s):  
Fluid Dynamics ◽  
Numerical Optimization ◽  
Single Point ◽  
Aerodynamic Performance ◽  
Aerodynamic Forces ◽  
Flow Solver ◽  
The Poor ◽  
Civil Aircraft ◽  
Shape Parameterization ◽  
Overall Performance

Airfoil design is essential for civil aircraft. A multi-point method is presented in this article to improve the aerodynamic performance of airfoil over a range of the flight envelope. This method combines computational fluid dynamics and numerical optimization. It comprises of three phases: 1) Airfoil shape parameterization method to develop candidate shapes. 2) Flow solver validation to calculate aerodynamic forces. 3) Searching for the optimized airfoil shape using the genetic algorithm. The major limitation of single-point design is the poor off-design performance. By basing the objective on a combination of the drag at three design points, the resulting overall performance can be improved with respect to the single-point result.

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