Wind Tunnel Experiments to Assess the Effect of Back-Mounted Radio Transmitters on Bird Body Drag

1988 ◽  
Vol 135 (1) ◽  
pp. 265-273 ◽  
Author(s):  
HOLLIDAY H. OBRECHT ◽  
C. J. PENNYCUICK ◽  
MARK R. FULLER

To whom reprint requests should be addressed. The aerodynamic drag of bird bodies was measured in a wind tunnel, with and without back-mounted dummy radio transmitters. Flight performance estimates indicate that the drag of a large transmitter can cause a substantial reduction of a migrant's range, that is, the distance it can cover in non-stop flight. The drag of the transmitter can be reduced by arranging the components in an elongated shape, so minimizing the frontal area. The addition of a rounded fairing to the front end, and a pointed fairing behind, was found to reduce the drag of the transmitter by about onethird, as compared with an unfaired rectangular box.

2019 ◽  
Vol 141 (5) ◽  
Author(s):  
Nur Alom ◽  
Ujjwal K. Saha

The elliptical-bladed Savonius wind turbine rotor has become a subject of interest because of its better energy capturing capability. Hitherto, the basic parameters of this rotor such as overlap ratio, aspect ratio, and number of blades have been studied and optimized numerically. Most of these studies estimated the torque and power coefficients (CT and CP) at given flow conditions. However, the two important aerodynamic forces, viz., the lift and the drag, acting on the elliptical-bladed rotor have not been studied. This calls for a deeper investigation into the effect of these forces on the rotor performance to arrive at a suitable design configuration. In view of this, at the outset, two-dimensional (2D) unsteady simulations are conducted to find the instantaneous lift and drag forces acting on an elliptical-bladed rotor at a Reynolds number (Re) = 0.892 × 105. The shear stress transport (SST) k–ω turbulence model is used for solving the unsteady Reynolds averaged Navier–Stokes equations. The three-dimensional (3D) unsteady simulations are then performed which are then followed by the wind tunnel experiments. The drag and lift coefficients (CD and CL) are analyzed for 0–360 deg rotation of rotor with an increment of 1 deg. The total pressure, velocity magnitude, and turbulence intensity contours are obtained at various angles of rotor rotation. For the elliptical-bladed rotor, the average CD, CL, and CP, from 3D simulation, are found to be 1.31, 0.48, and 0.26, respectively. The average CP for the 2D elliptical profile is found to be 0.34, whereas the wind tunnel experiments demonstrate CP to be 0.19.


Author(s):  
Yusuke Miyazaki ◽  
Kazuki Iida ◽  
Motomu Nakashima ◽  
Takeo Maruyama ◽  
Kaohru Yamanobe

To improve competitive skills, it is important to clarify the relationship between the propulsion motion (the propulsive force in the use of racing wheelchairs optimized for athletes) and aerodynamic drag, which can change during propulsive motion. Therefore, the purpose of this research was to construct a novel force sensor system that is attachable to racing wheelchairs for individual athletes and usable in a wind tunnel facility to examine differences in the push-rim force characteristics of athletes based on the measured results. The system was composed of four two-dimensional component force sensors, batteries, and radio transmitters. From the output of the four two-dimensional component sensors, tangential and radial components of the push-rim force were measured. Three top-class long-distance wheelchair athletes participated in this study, which required each athlete to push a racing wheelchair at 5.56 m/s on a wheelchair roller system in a wind tunnel facility. The force sensor system was mounted on the participants’ individual racing wheelchairs. The measured tangential force waveforms were classified as either bimodal or unimodal depending on the athletes’ propulsion styles. Although two athletes showed similar propulsion style characteristics, the athlete with more years of experience showed better propulsive work efficiency and repeatability. Therefore, a difference in skill for applying propulsive force during the push phase, which is difficult to estimate by kinematic analysis, could be estimated by using the force sensor system.


Author(s):  
J J C Chua ◽  
F K Fuss ◽  
A Subic

Tyre-caster systems such as wheelchairs consist of several components with different bearing and rolling friction, with the latter depending on the tyre pressure. The aim of this study was to determine the rolling friction of a rugby wheelchair with deflated and maximally inflated tyres. The rolling friction was determined with coast-down tests by instrumenting the wheelchair with an accelerometer. As the energy loss of coasting down comes primarily from the rolling friction and aerodynamic drag, the latter (including the lift) was determined using wind tunnel experiments. The ratio of the sum of horizontal forces (drag and inertial) to the sum of vertical forces (lift and gravitational) determined the rolling friction coefficient. The rolling friction coefficient expressed as a function of the velocity was found to be highly non-linear, consisting of an initial viscous spike at low velocities, a constant component, and a parabolic component increasing with velocity. The rolling friction coefficient of the wheelchair with deflated tyres was on average three times higher than the one with maximally inflated tyres.


Fluids ◽  
2021 ◽  
Vol 6 (1) ◽  
pp. 44
Author(s):  
Jeff Howell ◽  
Steve Windsor ◽  
Martin Passmore

The car aerodynamicist developing passenger cars is primarily interested in reducing aerodynamic drag. Considerably less attention is paid to the lift characteristics except in the case of high-performance cars. Lift, however, can have an effect on both performance and stability, even at moderate speeds. In this paper, the basic shape features which affect lift and the lift distribution, as determined from the axle loads, are examined from wind tunnel tests on various small-scale bodies representing passenger cars. In most cases, the effects of yaw are also considered. The front-end shape is found to have very little effect on overall lift, although it can influence the lift distribution. The shape of the rear end of the car, however, is shown to be highly influential on the lift. The add-on components and other features can have a significant effect on the lift characteristics of real passenger cars and are briefly discussed. The increase in lift at yaw is, surprisingly, almost independent of shape, as shown for the simple bodies. This characteristic is less pronounced on real passenger cars but lift increase at yaw is shown to rise with vehicle length.


Author(s):  
Tian Li ◽  
Ming Li ◽  
Zheng Wang ◽  
Jiye Zhang

In wind tunnel experiments, the inter-car gaps are designed in such a way as to separate the force measurements for each car and prevent the interference between cars during tests. Moreover, the inter-car gap has a significant effect on the aerodynamic drag of a train. In order to guide the design of the inter-car gaps between cars in wind tunnel experiments, the impact of the inter-car gap length on the aerodynamic characteristics of a 1/8th scale high-speed train is investigated using computational fluid dynamics. The shear stress transport k-ω model is used to simulate the flow around a high-speed train. The aerodynamic characteristics of the train with 10 different inter-car gap lengths are numerically simulated and compared. The 10 different inter-car gap lengths are 5, 8, 10, 15, 20, 30, 40, 50, 60, and 80 mm. Results indicate that the aerodynamic drag coefficients obtained using computational fluid dynamics fit the experimental data well. Rapid pressure variations appear in the upper and lower parts of the inter-car gaps. With the increase of the inter-car gap length, the drag force coefficient of the head car gradually increases. The total drag force coefficients of the trains with the inter-car gap length less than 10 mm are practically equal to those of the trains without inter-car gaps. Therefore, it can be concluded from the present study that 10 mm is recommended as the inter-car gap length for the 1/8th scale high-speed train models in wind tunnel experiments.


2014 ◽  
Vol 575 ◽  
pp. 300-305 ◽  
Author(s):  
Lalit Patidar ◽  
Sri Ramya Bhamidipati

Aerodynamic drag plays an important role in fuel economy of the vehicle especially for electric cars directly affecting the range. The objective of Aerodynamics subsystem of IIT Bombay racing team is to predict and minimize drag force on the Formula student electric race car thereby improving the performance. A standard generic car body known as Ahmed body is taken to set up simulation parameters in FLUENT by validating a test case against the experimental data available in literature. Variation and dependence of drag force on parameters such as frontal area, distribution of pressure coefficient and pressure loss in wake region is studied numerically. Comparison is made between Formula Student 2013 car Evo2 and newly designed car Evo3 for coming season of Formula Student 2014. A substantial reduction in drag force of 18.8% is achieved which can be attributed to lower frontal area and streamlined bodyworks design. Energy consumption of the vehicle for endurance race is reduced by 11.5 % improving the fuel economy.


2011 ◽  
Vol 60 (1) ◽  
pp. 87-102 ◽  
Author(s):  
Andrea Farsang ◽  
József Szatmári ◽  
Gábor Négyesi ◽  
Máté Bartus ◽  
Károly Barta

Összefoglalva megállapítható, hogy nagyobb szélsebesség hatására több talajanyag erodálódott, és ezzel együtt megnőtt az áthalmozott tápanyag mennyisége is. Minden vizsgált szélsebesség esetében a szélerózió következtében 3–7%-kal megnőtt az 1 mm és annál nagyobb szemcsék, illetve aggregátumok aránya a kiindulási talajanyag felső 0–1 cm-es rétegében. A finomabb szemcse-, illetve aggregátum-átmérők esetén a fújatást követően csökkenést tapasztaltunk. A leginkább a 315 μm és az annál kisebb szemcsék aránya csökkent, átlagosan 1–2%-kal. A minták kémiai és fizikai elemzéseiből megállapítható, hogy a láda utáni humuszosabb, aggregátumosabb szerkezetű minták N-tartalma nagyobb, mint az alapmintáé. A fogók mintáiban nem tapasztaltunk feldúsulást egy vizsgált elem esetében sem, a fogókban összegyűlt talajanyag kálium- és foszfortartalma is kisebb volt, mint az alapmintáé. Ennek oka, hogy az itt csapdázódott üledékben kisebb a tápanyag-megkötődés helyéül szolgáló leiszapolható rész aránya, mint a kiindulási talajanyagban. A vizsgálatainkból látszik, hogy a szélerózió hatására a lebegtetve, illetve ugráltatva áthalmozott talajszemcsékkel és aggregátumokkal szállított humusz 500–3500 kg/ha nagyságrendben mozoghat a vizsgált csernozjom területen akár egyetlen szélesemény hatására is. A kálium-áthalmozódás mértéke elérheti a 100 kg/ha értéket, a foszforé a 70 kg/ha-t, a nitrogénveszteség mértéke pedig akár 200–300 kg/ha is lehet egy szélesemény alkalmával. E tápanyagmennyiség nagy része több száz méter, de akár kilométeres távolságokra is távozhat a területről. Az általunk végzett szélcsatornás vizsgálatok eredményei becslésnek tekinthetők, hiszen vizsgálatunk során növénymaradvány-mentes, szitált és légszáraz talajanyaggal dolgoztunk. A szitálás eredményeként csupán a 2 mm-es és annál kisebb aggregátumok maradtak meg, ami azonban az intenzív művelés alá vont, porosodott, leromlott szerkezetű talajfelszín körülményeit jól közelíti. Ugyanakkor a természetben zajló széleróziós eseményeknek a szélcsatorna-kísérlet csak leegyszerűsített modellváltozata, hiszen az általunk szimulált szélesemények 15 percig tartottak, s nem tudtunk széllökéseket előállítani, melyek a széleróziós események alakulásában nagy jelentőségűek. Ennek tudatában kell a kapott eredményeket értékelni, mégis érdemes velük foglalkozni. A terepi mérésekkel szemben a szélcsatornában végzett vizsgálatoknak éppen az a legfontosabb előnye, hogy ellenőrzött, kontrollált körülmények között végezzük a méréseket, így rengeteg olyan szempontot meg tudunk vizsgálni, amit terepi mérésekkel lehetetlen lenne. Ilyen szempontok a pontos szélsebesség és szélirány hatása, az erodált felület nagysága és tulajdonságai. Kutatásunk következő lépése a szélcsatornás kísérletekkel vizsgált mintaterületeken terepi, mobil szélcsatornás vizsgálatok végzése, valamint terepi üledékcsapdák elhelyezésével a valós szélesemények által elszállított talaj mennyiségének és minőségének meghatározása. Célunk mind pontosabb képet alkotni a hazai jó minőségű csernozjom talajok szélerózió okozta tápanyagveszteségének mértékéről. A mezőgazdasági művelés alatt álló csernozjom területek feltalajában a tápanyag és szerves anyag szélerózió útján történő mozgási törvényszerűségeinek feltárása több szempontból is hasznos: segítséget jelent a területi tervezésben, a defláció szempontjából optimális területhasználat és művelési módok meghatározásában. Képet kapunk arról, hogy a legnagyobb gazdasági potenciállal rendelkező termőtalajunk milyen veszélyeknek van kitéve, s hogy a nem megfelelő időben, nem megfelelő nedvességviszonyok mellett történő talajművelés következtében kialakuló szerkezetromlás (porosodás) miatti deflációs károk milyen tápanyagveszteséggel járhatnak együtt.


2012 ◽  
Vol 28 (3) ◽  
pp. 317-323 ◽  
Author(s):  
Vincent Chabroux ◽  
Caroline Barelle ◽  
Daniel Favier

The present work is focused on the aerodynamic study of different parameters, including both the posture of a cyclist’s upper limbs and the saddle position, in time trial (TT) stages. The aerodynamic influence of a TT helmet large visor is also quantified as a function of the helmet inclination. Experiments conducted in a wind tunnel on nine professional cyclists provided drag force and frontal area measurements to determine the drag force coefficient. Data statistical analysis clearly shows that the hands positioning on shifters and the elbows joined together are significantly reducing the cyclist drag force. Concerning the saddle position, the drag force is shown to be significantly increased (about 3%) when the saddle is raised. The usual helmet inclination appears to be the inclination value minimizing the drag force. Moreover, the addition of a large visor on the helmet is shown to provide a drag coefficient reduction as a function of the helmet inclination. Present results indicate that variations in the TT cyclist posture, the saddle position and the helmet visor can produce a significant gain in time (up to 2.2%) during stages.


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