scholarly journals Overcoming Stopovers in Cycloidal Rotor Propulsion Integration on Air Vehicles

2012 ◽  
Author(s):  
José C. Páscoa ◽  
Galina I. Ilieva
Keyword(s):  
Large Scale ◽  
Reynolds Numbers ◽  
Rotational Axis ◽  
Major Drawback ◽  
Drag Forces ◽  
Flow Mechanisms ◽  
Weight Penalty ◽  
Thrust Vector ◽  
Lift And Drag ◽  
Rotating Wing

A cyclorotor (also known as a cyclocopter or cyclogiro) is a rotating-wing system where the span of the blades runs parallel to the axis of its rotation. The pitch angle of each of the blades is varied cyclically by mechanical means such that the blades experiences positive angles of attack at both the top and bottom positions of the azimuth cycle. The resulting time-varying lift and drag forces produced by each blade can be resolved into the vertical and horizontal directions. Varying the amplitude and phase of the cyclic blade pitch can be used to change the magnitude and direction of the net thrust vector produced by the cyclorotor. Compared to a conventional rotor, each spanwise blade element of a cyclorotor operates at similar aerodynamic conditions (i.e., at similar flow velocities, Reynolds numbers, and angles of incidence), and so the blades can be optimized to achieve the best aerodynamic efficiency. Moreover, because the blades are cyclically pitched once per revolution (1/rev), unsteady flow mechanisms may delay blade stall onset and in turn may augment the lift produced by the blades. Albeit proposed to MAV-scale, its use on large scale vehicles turns problematic, and we proposed in this paper to address their stopovers. Furthermore, since the thrust vector of a cyclorotor can be instantaneously set to any direction perpendicular to the rotational axis, a cyclorotor-based air vehicle may ultimately show better maneuverability and agility as compared to a classical powered conventional rotor system. One major drawback of a cyclorotor is its relatively large rotating structure which might offer a weight penalty when compared to a conventional rotor.

A Novel Look at the Performance of the Cyclorotor Propulsion System for Air Vehicles

2012 ◽  
Author(s):  
José C. Páscoa ◽  
Antonio Dumas ◽  
Michele Trancossi
Keyword(s):  
Large Scale ◽  
Reynolds Numbers ◽  
Unsteady Motion ◽  
Rotational Axis ◽  
Rotor Systems ◽  
Drag Forces ◽  
Blade Optimization ◽  
Weight Penalty ◽  
Lift And Drag ◽  
Rotating Wing

A system in which a rotating-wing device, comprising several pitching blades, turns around an axis along the span of the blades is called a cyclorotor. During the azimuthal rotation of the blades they also experience a change in the pitch angle. For each of the blades its pitch is varied cyclically by mechanical means such that the blades experience positive angles of attack at both the top and bottom positions of the azimuth cycle. The resultant unsteady motion of each blade can then be summed up into a resultant lift and drag forces. An almost instantaneous variation of magnitude and direction of the total cyclo rotor thrust can be obtained by changing the amplitude and phase of the cyclic blade pitch. In this rotor, conversely to classical propellers, each spanwise blade element operates at similar flow velocities, Reynolds numbers and incidence, this allows an easier blade optimization to achieve the best aerodynamic efficiency. Further, the cyclorotor is based on using dynamic pitching in order to delay stall and in this way increase the lift produced by the blades. Realistic flying vehicles have only be presented for the MAV-scale, its use on large scale vehicles turns problematic, herein we will analyze its stopovers. Finally, a very advantageous characteristic is the possibility to achieve almost instantaneous thrust variation in any direction perpendicular to the rotational axis, this will result in an air vehicle with a much better maneuverability, as compared with vehicles powered by classical rotor systems. This comes at a cost of a larger structure which might lead to a weight penalty.

On the reverse swing of a cricket ball—modelling and measurements

2001 ◽  
Vol 215 (1) ◽  
pp. 45-55 ◽  
Author(s):  
A T Sayers
Keyword(s):  
Boundary Layer ◽  
Flow Visualization ◽  
Reynolds Numbers ◽  
Flow Conditions ◽  
Drag Forces ◽  
Cricket Ball ◽  
Direct Measurements ◽  
Scale Ratio ◽  
Lift And Drag ◽  
At Will

The phenomenon of reverse swing of the ball in a game of cricket is achieved by very few bowlers, and then only by those who seem able to bowl at speeds in excess of 85 mile/h. It also seems that reverse swing cannot be achieved at will. Rather, it is obtained perhaps by accident as much as by design, its inception being as much of a surprise to the bowler as to the batsman. This would suggest that the flow conditions pertaining to reverse swing are extremely marginal at best. This paper investigates the flow conditions required for reverse swing to occur and presents data describing the lift and drag on the ball. While some direct measurements are made on a cricket ball for comparison purposes, the flow over the ball is modelled through a 2.7:1 scale ratio sphere. This permitted relatively large lift and drag forces to be measured. The results define the range of Reynolds numbers and seam angles over which reverse swing will occur, as well as the corresponding forces on the cricket ball. Flow visualization is used to indicate the state of the boundary layer.

Vortex-Excited Response of Large-Scale Cylinders in Sheared Flow

1988 ◽  
Vol 110 (3) ◽  
pp. 272-277 ◽  
Author(s):  
J. A. Humphries ◽  
D. H. Walker
Keyword(s):  
Large Scale ◽  
Shear Velocity ◽  
Reynolds Numbers ◽  
Hydrodynamic Drag ◽  
Flow Induced Vibration ◽  
Sheared Flow ◽  
Drag Forces ◽  
Linear Shear ◽  
Series Of Experiments ◽  
The Mean

A series of experiments were performed to measure the vortex-excited response of a 0.168-m-dia slender circular cylinder in a range of linear shear velocity profiles. Reynolds numbers of up to 2.5 × 105 were achieved. The results clearly showed that regular large-amplitude cylinder vibrations occurred well within the critical drag transition region. It was found that increasing the linear shear profile decreased the peak amplitude response but broadened the range of lock-on over which large oscillations occurred. The flow-induced vibration of the cylinder caused amplification of the mean hydrodynamic drag forces acting on the cylinder when compared with those expected for a similar rigid cylinder.

Dragonfly flight. I. Gliding flight and steady-state aerodynamic forces.

1997 ◽  
Vol 200 (3) ◽  
pp. 543-556 ◽  
Author(s):  
JM Wakeling ◽  
CP Ellington
Keyword(s):  
Steady State ◽  
Lift Coefficient ◽  
Reynolds Numbers ◽  
The Body ◽  
Flat Plates ◽  
Viscous Forces ◽  
Drag Forces ◽  
Aerodynamic Properties ◽  
Gliding Flight ◽  
Lift And Drag

The free gliding flight of the dragonfly Sympetrum sanguineum was filmed in a large flight enclosure. Reconstruction of the glide paths showed the flights to involve accelerations. Where the acceleration could be considered constant, the lift and drag forces acting on the dragonfly were calculated. The maximum lift coefficient (CL) recorded from these glides was 0.93; however, this is not necessarily the maximum possible from the wings. Lift and drag forces were additionally measured from isolated wings and bodies of S. sanguineum and the damselfly Calopteryx splendens in a steady air flow at Reynolds numbers of 700-2400 for the wings and 2500-15 000 for the bodies. The maximum lift coefficients (CL,max) were 1.07 for S. sanguineum and 1.15 for C. splendens, which are greater than those recorded for all other insects except the locust. The drag coefficient at zero angle of attack ranged between 0.07 and 0.14, being little more than the Blassius value predicted for flat plates. Dragonfly wings thus show exceptional steady-state aerodynamic properties in comparison with the wings of other insects. A resolved-flow model was tested on the body drag data. The parasite drag is significantly affected by viscous forces normal to the longitudinal body axis. The linear dependence of drag on velocity must thus be included in models to predict the parasite drag on dragonflies at non-zero body angles.

scholarly journals Design, Modeling, and Simulation of a Wing Sail Land Yacht

2021 ◽  
Vol 11 (6) ◽  
pp. 2760
Author(s):  
Vítor Tinoco ◽  
Benedita Malheiro ◽  
Manuel F. Silva
Keyword(s):  
Modeling And Simulation ◽  
3D Model ◽  
Angular Position ◽  
Simulation Method ◽  
Polar Diagram ◽  
Control Techniques ◽  
Drag Forces ◽  
Lift And Drag ◽  
Rotating Wing ◽  
Novel Design

Autonomous land yachts can play a major role in the context of environmental monitoring, namely, in open, flat, windy regions, such as iced planes or sandy shorelines. This work addresses the design, modeling, and simulation of a land yacht probe equipped with a rigid free-rotating wing sail and tail flap. The wing was designed with a symmetrical airfoil and dimensions to provide the necessary thrust to displace the vehicle. Specifically, it proposes a novel design and simulation method for free rotating wing sail autonomous land yachts. The simulation relies on the Gazebo simulator together with the Robotic Operating System (ROS) middleware. It uses a modified Gazebo aerodynamics plugin to generate the lift and drag forces and the yawing moment, two newly created plugins, one to act as a wind sensor and the other to set the wing flap angular position, and the 3D model of the land yacht created with Fusion 360. The wing sail aligns automatically to the wind direction and can be set to any given angle of attack, stabilizing after a few seconds. Finally, the obtained polar diagram characterizes the expected sailing performance of the land yacht. The described method can be adopted to evaluate different wing sail configurations, as well as control techniques, for autonomous land yachts.

Design Optimization and Analysis of NACA 0012 Airfoil Using Computational Fluid Dynamics and Genetic Algorithm

2014 ◽  
Vol 664 ◽  
pp. 111-116 ◽  
Author(s):  
R.K. Ganesh Ram ◽  
Yashaan Nari Cooper ◽  
Vishank Bhatia ◽  
R. Karthikeyan ◽  
C. Periasamy
Keyword(s):  
Reynolds Numbers ◽  
Ansys Fluent ◽  
Airfoil Optimization ◽  
Drag Forces ◽  
Fluent Software ◽  
Numerical Computing ◽  
Cfd Method ◽  
Lift And Drag ◽  
Naca 0012 ◽  
Mathematical Relations

CFD method is inexpensive method of analysis of flow over aerodynamic structure. It incorporates mathematical relations and algorithms to analyze and solve the problems regarding fluid flow. CFD analysis of an airfoil produces results such as lift and drag forces which determines the ability of an airfoil. Optimization of an airfoil involves improving the design of the airfoil in order to manipulate the lift and drag coefficients according to the requirements. It is a very common method used in all fields of engineering. MATLAB is a numerical computing environment which supports interface with other software. XFoil is airfoil analysis software which calculates the lift and drag characteristics for different Reynolds numbers, Mach numbers and angles of attack. MALAB is interfaced with XFoil and the optimization of NACA 0012 airfoil is done and the results are analyzed. The performance of optimized air foil is analyzed using ANSYS FLUENT software.

Unsteady numerical investigation of two different corrugated airfoils

2016 ◽  
Vol 231 (13) ◽  
pp. 2423-2437 ◽  
Author(s):  
WH Ho ◽  
TH New
Keyword(s):  
Large Scale ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Reynolds Numbers ◽  
Mean Flow ◽  
Airfoil Surface ◽  
Low Reynolds Numbers ◽  
Corrugated Surfaces ◽  
Large Scale Flow ◽  
Lift And Drag

An unsteady, two-dimensional numerical study was conducted to investigate the aerodynamic and flow characteristics of two bio-inspired corrugated airfoils at Re = 14,000 and compared with those of a smooth NACA0010 airfoil. Mean aerodynamic results reveal that the corrugated airfoils have better lift performance compared to the NACA0010 airfoil but incur slightly higher drag penalty. Mean flow streamlines indicate that this favourable performance is due to the ability of the corrugated airfoils in mitigating large-scale flow separations and stall. Unsteady flow field results show persistent formations of small recirculating vortices that remain within the corrugations at 10° angle-of-attack or less for one of the corrugated airfoil and below 15° for the other. In contrast, the flow behaviour can be highly turbulent with regular pairings of large-scale flow separation vortices along the upper surface at higher angles-of-attack. This not only disrupts the small recirculating vortices and causes them to detach from the corrugated surfaces, but it gets increasingly dominant at higher angles-of-attack resulting in regular lift and drag oscillations. At the end of each cycle, there is a sudden ejection of flow perpendicular to the airfoil surface and these disruptions manifest themselves as “kinks” in the instantaneous lift and drag of the corrugated airfoils. Therefore instead of regular fluctuations, the lift and drag curves have additional undulations. Despite that, the corrugations are able to produce larger pressure differentials between the upper and lower surfaces than the smooth airfoil. The current study demonstrates the intricate relationships between different sharp surface corrugations and favourable aerodynamic performance. In particular, results from this paper supports earlier investigations that corrugated airfoils may be used to good effects even at low Reynolds numbers, where flow separations are more likely.

Investigation of Large-Scale Cooling System Fan Blade Vibration

2014 ◽  
Author(s):  
Jacques Muiyser ◽  
Danie N. J. Els ◽  
Sybrand J. van der Spuy ◽  
Albert Zapke
Keyword(s):  
Large Scale ◽  
Cooling System ◽  
Vibrational Amplitude ◽  
Flow Conditions ◽  
Blade Vibration ◽  
Aerodynamic Loads ◽  
Drag Forces ◽  
Fan Blade ◽  
Lift And Drag ◽  
Do So

Fans operating at the edges of large-scale air-cooled steam condensers often do so under distorted inlet air flow conditions. These conditions create variations in the aerodynamic loads exerted on a fan blade during rotation which causes it to vibrate. In order to isolate the sources of the unsteady aerodynamic loads as well as their effects on blade vibration, a potential flow fluid dynamics code was written to determine the aerodynamic loads exerted on a fan blade as a function of its rotation. The lift and drag forces were exported to a finite element code approximating the fan blade as a cantilever beam. With these two sets of code the response of the blade when subjected to varying aerodynamic loads could be determined. Furthermore, the effect of changing certain parameters such as blade stiffness or damping can be investigated. It was found that the blade’s response closely resembles that which was measured at the full-scale facility and that slight changes to the blade’s stiffness can potentially reduce the vibrational amplitude but may also lead to resonance.

Effects of smart flap on aerodynamic performance of sinusoidal leading-edge wings at low Reynolds numbers

2020 ◽  
pp. 095441002094690
Author(s):  
AA Mehraban ◽  
MH Djavareshkian ◽  
Y Sayegh ◽  
B Forouzi Feshalami ◽  
Y Azargoon ◽  
...  
Keyword(s):  
High Performance ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Low Reynolds Numbers ◽  
Drag Forces ◽  
Wide Range ◽  
Beam Bending ◽  
Low Reynolds ◽  
Lift And Drag ◽  
Drag Ratio

Sinusoidal leading-edge wings have shown a high performance after the stall region. In this study, the role of smart flaps in the aerodynamics of smooth and sinusoidal leading-edge wings at low Reynolds numbers of 29,000, 40,000 and 58,000 is investigated. Four wings with NACA 634-021 profile are firstly designed and then manufactured by a 3 D printer. Beam bending equation is used to determine the smart flap chord deflection. Next, wind tunnel tests are carried out to measure the lift and drag forces of proposed wings for a wide range of angles of attack, from zero to 36 degrees. Results show that using trailing-edge smart flap in sinusoidal leading-edge wing delays the stall point compared to the same wing without flap. However, a combination of smooth leading-edge wing and smart flap advances the stall. Furthermore, it is found that wings with smart flap generally have a higher lift to drag ratio due to their excellent performance in producing lift.

Vortex force map method for viscous flows of general airfoils

2017 ◽  
Vol 836 ◽  
pp. 145-166 ◽  
Author(s):  
Juan Li ◽  
Zi-Niu Wu
Keyword(s):  
Flat Plate ◽  
Normal Force ◽  
Viscous Flows ◽  
Reynolds Numbers ◽  
The Body ◽  
Drag Forces ◽  
Edge Force ◽  
Lift And Drag ◽  
Critical Regions ◽  
Map Approach

In a previous paper, an inviscid vortex force map approach was developed for the normal force of a flat plate at arbitrarily high angle of attack and leading/trailing edge force-producing critical regions were identified. In this paper, this vortex force map approach is extended to viscous flows and general airfoils, for both lift and drag forces due to vortices. The vortex force factors for the vortex force map are obtained here by using Howe’s integral force formula. A decomposed form of the force formula, ensuring vortices far away from the body have negligible effect on the force, is also derived. Using Joukowsky and NACA0012 airfoils for illustration, it is found that the vortex force map for general airfoils is similar to that of a flat plate, meaning that force-producing critical regions similar to those of a flat plate also exist for more general airfoils and for viscous flow. The vortex force approach is validated against NACA0012 at several angles of attack and Reynolds numbers, by using computational fluid dynamics.

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