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.

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.

Computational Aerodynamics of a Winston-Cup-Series Race Car

2002 ◽  
Author(s):  
Oktay Baysal ◽  
Terry L. Meek
Keyword(s):  
Present Model ◽  
Pressure Coefficient ◽  
The Body ◽  
Race Car ◽  
Drag Forces ◽  
Surface Pressure Distribution ◽  
Computational Aerodynamics ◽  
Baseline Case ◽  
Quantitative Results ◽  
Lift And Drag

Since the goal of racing is to win and since drag is a force that the vehicle must overcome, a thorough understanding of the drag generating airflow around and through a race car is greatly desired. The external airflow contributes to most of the drag that a car experiences and most of the downforce the vehicle produces. Therefore, an estimate of the vehicle’s performance may be evaluated using a computational fluid dynamics model. First, a computer model of the race car was created from the measurements of the car obtained by using a laser triangulation system. After a computer-aided drafting model of the actual car was developed, the model was simplified by removing the tires, roof strakes, and modification of the spoiler. A mesh refinement study was performed by exploring five cases with different mesh densities. By monitoring the convergence of the computed drag coefficient, the case with 2 million elements was selected as being the baseline case. Results included flow visualization of the pressure and velocity fields and the wake in the form of streamlines and vector plots. Quantitative results included lift and drag, and the body surface pressure distribution to determine the centerline pressure coefficient. When compared with the experimental results, the computed drag forces were comparable but expectedly lower than the experimental data mainly attributable to the differences between the present model and the actual car.

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.

Controlling subterranean forces enables a fast, steerable, burrowing soft robot

2021 ◽  
Vol 6 (55) ◽  
pp. eabe2922
Author(s):  
Nicholas D. Naclerio ◽  
Andras Karsai ◽  
Mason Murray-Cooper ◽  
Yasemin Ozkan-Aydin ◽  
Enes Aydin ◽  
...  
Keyword(s):  
Granular Media ◽  
The Body ◽  
Nonlinear Dependence ◽  
Soft Robot ◽  
Flow Angle ◽  
Drag Forces ◽  
Tip Extension ◽  
Order Of Magnitude ◽  
Lift And Drag ◽  
And Control

Robotic navigation on land, through air, and in water is well researched; numerous robots have successfully demonstrated motion in these environments. However, one frontier for robotic locomotion remains largely unexplored—below ground. Subterranean navigation is simply hard to do, in part because the interaction forces of underground motion are higher than in air or water by orders of magnitude and because we lack for these interactions a robust fundamental physics understanding. We present and test three hypotheses, derived from biological observation and the physics of granular intrusion, and use the results to inform the design of our burrowing robot. These results reveal that (i) tip extension reduces total drag by an amount equal to the skin drag of the body, (ii) granular aeration via tip-based airflow reduces drag with a nonlinear dependence on depth and flow angle, and (iii) variation of the angle of the tip-based flow has a nonmonotonic effect on lift in granular media. Informed by these results, we realize a steerable, root-like soft robot that controls subterranean lift and drag forces to burrow faster than previous approaches by over an order of magnitude and does so through real sand. We also demonstrate that the robot can modulate its pullout force by an order of magnitude and control its direction of motion in both the horizontal and vertical planes to navigate around subterranean obstacles. Our results advance the understanding and capabilities of robotic subterranean locomotion.

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.

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.

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.

Fluid forces on a body in shear-flow; experimental use of ‘stationary flow'

1974 ◽  
Vol 340 (1621) ◽  
pp. 147-171 ◽  
Keyword(s):  
Shear Flow ◽  
Lift Force ◽  
Force Measurement ◽  
Fluid Velocity ◽  
Stationary Flow ◽  
The Body ◽  
Fluid Forces ◽  
Drag Forces ◽  
Lift And Drag ◽  
Repulsive Forces

The lift and drag forces have been measured on a sphere and a transverse cylinder immersed in an open liquid shear-flow and situated close to the lower, frictional, boundary (the bed). Two conditions were investigated: ( a ) that of zero drag, when the body was drifting with the flow, and ( b ) that when it was held against the flow. In condition ( a ) the body could be either allowed to rotate about a transverse axis subject to unavoidable pivot friction, or prevented from rotating. Marked difference was found in the magnitude of the lift force according to the applied resistance to rotation. The lift force was a maximum when rotation was prevented and small or undetectable when free rotation was allowed. In the conditions ( a ) and ( b ) the lift force decreased with increasing clearance between body and boundary, to zero when the clearance exceeded approximately one body diameter. In condition ( b ) lift, i. e. normally repulsive, forces of approximately equal magnitudes to those below were exerted as the body approached the upper free liquid surface. In the drifting condition ( a ) the considerable difficulties of observation and force measurement when a body is moving with the flow were removed by the use of a backward-moving bed boundary. By thus superimposing a reverse velocity on the whole system, the mean fluid velocity at any desired distance from the boundary can be made zero relative to the observer without appreciably affecting the internal dynamics of the flow. This device also permitted the repetition of the measurements made by using liquids of greater viscosity than water available in limited quantities. The results are interpreted with an explanation in mind of certain aspects of the motions of unsuspended solids in saltation over a stream bed.

Simulation of Viscous Diffusion for Extension of the Surface Vorticity Method to Boundary Layer and Separated Flows

1981 ◽  
Vol 23 (3) ◽  
pp. 157-167 ◽  
Author(s):  
D. T. C. Porthouse ◽  
R. I. Lewis
Keyword(s):  
Boundary Layer ◽  
Flow Separation ◽  
Point Vortex ◽  
Fluid Flows ◽  
Reynolds Numbers ◽  
Separated Flows ◽  
Two Dimensional ◽  
Drag Forces ◽  
Boundary Layer Parameter ◽  
Lift And Drag

A numerical method for two-dimensional incompressible viscous fluid flows is tested on the diffusion of a point vortex. It is then applied to the boundary layer to reconstruct the Blasius profile, to demonstrate flow separation, and to simulate turbulence. The significance of Thwaites' boundary layer parameter for flow separation is explained. The Kelvin-Helmholtz instability, which is responsible for two-dimensional turbulence, is represented by the motion of an array of point vortices after an initial disturbance. The formation of the Von Karman vortex street downstream of a circular cylinder is described by computer simulation, and the influence of viscous diffusion is shown. For two different cylinder Reynolds numbers the vortex shedding frequencies and oscillating lift and drag forces are evaluated.

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