Perspective: Unsteady Wing Theory—The Ka´rma´n/Sears Legacy

1993 ◽  
Vol 115 (4) ◽  
pp. 548-560 ◽  
Author(s):  
J. E. McCune ◽  
T. S. Tavares
Keyword(s):  
Aspect Ratio ◽  
Small Amplitude ◽  
Leading Edge ◽  
Aerodynamic Characteristics ◽  
Unsteady Motion ◽  
Low Aspect Ratio ◽  
Key Concepts ◽  
Edge Separation ◽  
Point Of Departure ◽  
Large Amplitude Motion

The aerodynamic analysis of wings and their vortex wakes is discussed from a perspective of its relation to the 1938 work of Ka´rma´n and Sears. The key concepts from this early paper on the analysis of airfoils in small amplitude unsteady motion are reviewed. These concepts are then used as a point of departure for developing techniques for calculating and interpreting the aerodynamic characteristics of both airfoils in large amplitude motion with deforming vortex wakes, and maneuvering low-aspect-ratio wings with leading-edge separation. Calculated examples are presented for this extended set of applications, and are compared to related analyses and experiments.

Aerodynamic Investigations of Low-Aspect-Ratio Thin Plate Wings at Low Reynolds Numbers

2012 ◽  
Vol 28 (1) ◽  
pp. 77-89 ◽  
Author(s):  
Y.-C. Liu ◽  
F.-B. Hsiao
Keyword(s):  
Aspect Ratio ◽  
Thin Plate ◽  
Angle Of Attack ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Aerodynamic Characteristics ◽  
Flow Structures ◽  
Low Aspect Ratio ◽  
Aerodynamic Properties ◽  
Stall Angle

ABSTRACTTo realize the relationship between flow structures of wingtip vortices and post stall characteristics of low aspect-ratio wings, this paper experimentally studies the aerodynamic characteristics and the corresponding flow structures of the rectangular thin-plate wings at Reynolds numbers between 104 and 105. The aerodynamic properties to be studied include lift, drag, slopes at linear and nonlinear range of the lift curves and lift-to-drag ratios of the tested wings with the aspect ratio varying from 1.0 to 3.0. The flow structures regarding the leading-edge separation vortices and wingtip vortices at upper surface and near-wake regions of the wings are also investigated by smoke-wire visualization. Results indicate that the high stall angle of attack and vortex lift are clearly manifested to induce the nonlinear increase in the lift curves as the aspect ratio reaches less than 1.6. This phenomenon is specifically observed to augment the aerodynamic properties with the decrease of the aspect ratio. Additionally, the corresponding flow visualization also indicates that the wingtip vortices and the areas of highly affected regions are duly increased with the increase of the angle of attack up to 40°, which makes certain that the extra increase of the nonlinear lift results from these vortices. This result can be practically applied to the planform design for unmanned aerial vehicles.

scholarly journals Secondary Flow Control in Low Aspect Ratio Vanes Using Splitters

2016 ◽  
Author(s):  
Christopher Clark ◽  
Graham Pullan ◽  
Eric Curtis ◽  
Frederic Goenaga
Keyword(s):  
Kinetic Energy ◽  
Aspect Ratio ◽  
Secondary Flow ◽  
Current Practice ◽  
Leading Edge ◽  
Horseshoe Vortex ◽  
Secondary Flows ◽  
Optimization Approach ◽  
Flow Strength ◽  
Low Aspect Ratio

Low aspect ratio vanes, often the result of overall engine architecture constraints, create strong secondary flows and high endwall loss. In this paper, a splitter concept is demonstrated that reduces secondary flow strength and improves stage performance. An analytic conceptual study, corroborated by inviscid computations, shows that the total secondary kinetic energy of the secondary flow vortices is reduced when the number of passages is increased and, for a given number of vanes, when the inlet endwall boundary layer is evenly distributed between the passages. Viscous computations show that, for this to be achieved in a splitter configuration, the pressure-side leg of the low aspect ratio vane horseshoe vortex, must enter the adjacent passage (and not “jump” in front of the splitter leading edge). For a target turbine application, four vane designs were produced using a multi-objective optimization approach. These designs represent: current practice for a low aspect ratio vane; a design exempt from thickness constraints; and two designs incorporating splitter vanes. Each geometry is tested experimentally, as a sector, within a low-speed turbine stage. The vane designs with splitters geometries were found to reduce the measured secondary kinetic energy, by up to 85%, to a value similar to the design exempt from thickness constraints. The resulting flowfield was also more uniform in both the circumferential and radial directions. One splitter design was selected for a full annulus test where a mixed-out loss reduction, compared to the current practice design, of 15.3% was measured and the stage efficiency increased by 0.88%.

Leading Edge and Wing Tip Flow Control on Low Aspect Ratio Wings

2010 ◽  
Author(s):  
Stefan Vey ◽  
David Greenblatt ◽  
Christian Nayeri ◽  
Christian Paschereit
Keyword(s):  
Aspect Ratio ◽  
Flow Control ◽  
Leading Edge ◽  
Low Aspect Ratio ◽  
Wing Tip ◽  
Low Aspect Ratio Wings

scholarly journals On the lift-optimal aspect ratio of a revolving wing at low Reynolds number

2018 ◽  
Vol 15 (143) ◽  
pp. 20170933 ◽  
Author(s):  
T. Jardin ◽  
T. Colonius
Keyword(s):  
Aspect Ratio ◽  
Lift Coefficient ◽  
Leading Edge ◽  
Rossby Number ◽  
Subsequent Work ◽  
High Lift ◽  
Low Aspect Ratio ◽  
Axis Of Rotation ◽  
Edge Vortex ◽  
Convergent Solution

Lentink & Dickinson (2009 J. Exp. Biol. 212 , 2705–2719. ( doi:10.1242/jeb.022269 )) showed that rotational acceleration stabilized the leading-edge vortex on revolving, low aspect ratio (AR) wings and hypothesized that a Rossby number of around 3, which is achieved during each half-stroke for a variety of hovering insects, seeds and birds, represents a convergent high-lift solution across a range of scales in nature. Subsequent work has verified that, in particular, the Coriolis acceleration plays a key role in LEV stabilization. Implicit in these results is that there exists an optimal AR for wings revolving about their root, because it is otherwise unclear why, apart from possible morphological reasons, the convergent solution would not occur for an even lower Rossby number. We perform direct numerical simulations of the flow past revolving wings where we vary the AR and Rossby numbers independently by displacing the wing root from the axis of rotation. We show that the optimal lift coefficient represents a compromise between competing trends with competing time scales where the coefficient of lift increases monotonically with AR, holding Rossby number constant, but decreases monotonically with Rossby number, when holding AR constant. For wings revolving about their root, this favours wings of AR between 3 and 4.

Effects of leading-edge separation on the vortex shedding and aerodynamic characteristics of an elongated bluff body

2020 ◽  
Vol 206 ◽  
pp. 104356
Author(s):  
Guiyue Duan ◽  
Shujin Laima ◽  
Wenli Chen ◽  
Hui Li
Keyword(s):  
Vortex Shedding ◽  
Bluff Body ◽  
Leading Edge ◽  
Aerodynamic Characteristics ◽  
Edge Separation

Numerical investigation of leading-edge vortex for low-aspect ratio thin wings

AIAA Journal ◽  
1976 ◽  
Vol 14 (2) ◽  
pp. 253-255 ◽  
Author(s):  
Colmar Rehbach
Keyword(s):  
Aspect Ratio ◽  
Numerical Investigation ◽  
Leading Edge ◽  
Leading Edge Vortex ◽  
Low Aspect Ratio ◽  
Edge Vortex

Aerodynamic characteristics of low-aspect-ratio prismatic bodies near a screen

1971 ◽  
Vol 3 (2) ◽  
pp. 73-74
Author(s):  
G. E. Khudyakov
Keyword(s):  
Aspect Ratio ◽  
Aerodynamic Characteristics ◽  
Low Aspect Ratio ◽  
Prismatic Bodies
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