The Alula and Its Aerodynamic Effect on Avian Flight

2007 ◽  
Author(s):  
Bridget Austin ◽  
Ann M. Anderson
Keyword(s):  
Lift Coefficient ◽  
Aix Sponsa ◽  
Bird Flight ◽  
Avian Flight ◽  
Minimum Drag ◽  
Lesser Scaup ◽  
Aythya Americana ◽  
Image Velocimetry ◽  
Stall Angle ◽  
Wood Duck

The alula, a small thumb-like appendage on a bird wing, is often credited with increasing lift and decreasing the risk of stall during bird flight. Using field based studies; researchers have observed that the alula lifts away from the wing at critical moments in flight, such as take-off and landing. However, to date, there has been no conclusive experimental evidence to support the idea that use of the alula affects lift. To determine the effect of the alula on avian flight, we used a wind tunnel to study the wings of four ducks: the Wood Duck (Aix sponsa), the Redhead Duck (Aythya americana), the Black Scoter (Melanitta americana), and the Lesser Scaup (Aythya affinis). We used a combination of lift/drag measurements and Particle Image Velocimetry (PIV) to test the wings at velocities from 10–16 m/s and angles of attack from −20 to 25 degrees. The alula was observed to naturally lift as the stall angle was approached. Of the four wings, the Black Scoter demonstrated the largest maximum lift coefficient (1.4), followed by the Wood Duck (1.3), the Lesser Scaup (1.2) and lastly, the Redhead Duck (0.9). All four wings had minimum drag coefficients near 0.1. The Lesser Scaup was the only wing which had a measurable change in lift (10%) attributable to alula deployment. PIV results for the flow field around the Lesser Scaup wing showed higher velocities on the top side of the wing when the alula was deflected.

Wind Tunnel Experimental Study of Wind Turbine Airfoil Aerodynamic Characteristics

2012 ◽  
Vol 260-261 ◽  
pp. 125-129
Author(s):  
Xin Zi Tang ◽  
Xu Zhang ◽  
Rui Tao Peng ◽  
Xiong Wei Liu
Keyword(s):  
Wind Tunnel ◽  
Wind Turbine ◽  
Lift Coefficient ◽  
Turbine Blades ◽  
Aerodynamic Characteristics ◽  
Wind Turbine Blades ◽  
High Lift ◽  
Minimum Drag ◽  
Stall Angle ◽  
High Reynolds

High lift and low drag are desirable for wind turbine blade airfoils. The performance of a high lift airfoil at high Reynolds number (Re) for large wind turbine blades is different from that at low Re number for small wind turbine blades. This paper investigates the performance of a high lift airfoil DU93-W-210 at high Re number in low Re number flows through wind tunnel testing. A series of low speed wind tunnel tests were conducted in a subsonic low turbulence closed return wind tunnel at the Re number from 2×105to 5×105. The results show that the maximum lift, minimum drag and stall angle differ at different Re numbers. Prior to the onset of stall, the lift coefficient increases linearly and the slope of the lift coefficient curve is larger at a higher Re number, the drag coefficient goes up gradually as angle of attack increases for these low Re numbers, meanwhile the stall angle moves from 14° to 12° while the Re number changes from 2×105to 5×105.

scholarly journals Experimental Investigation of Lift Enhancement and Drag Reduction of Discrete Co-Flow Jet Rotor Airfoil

2021 ◽  
Vol 11 (20) ◽  
pp. 9561
Author(s):  
Shunlei Zhang ◽  
Xudong Yang ◽  
Bifeng Song ◽  
Zhuoyuan Li ◽  
Bo Wang
Keyword(s):  
Drag Reduction ◽  
High Performance ◽  
Performance Enhancement ◽  
Fundamental Problem ◽  
Unit Length ◽  
Lift Coefficient ◽  
Angle Of Attack ◽  
Relative Unit ◽  
Lift Enhancement ◽  
Stall Angle

Rotor airfoil design involves multi-point and multi-objective complex constraints. How to significantly improve the maximum lift coefficient and lift-to-drag ratio of rotor airfoil is a fundamental problem, which should be solved urgently in the development of high-performance helicopter rotor blades. To address this, discrete co-flow jet (DCFJ) technology is one methods with the most potential that can be harnessed to improve the performance of the rotor airfoil. In this study, wind tunnel experiments are conducted to study the effect of DCFJ technology on lift enhancement and drag reduction of OA312 airfoil. Furthermore, the performance improvement effects of the open co-flow jet (CFJ) and DCFJ technologies are studied. In addition, the influence of fundamental parameters, such as the obstruction factor and relative unit length, are analyzed. Results demonstrate that DCFJ technology is better than CFJ technology on the performance enhancement of the OA312 airfoil. Moreover, the DCFJ rotor airfoil can significantly reduce the drag coefficient and increase the maximum lift coefficient and the stall angle of attack. The maximum lift coefficient can be increased by nearly 67.3%, and the stall angle of attack can be delayed by about 12°. The DCFJ rotor airfoil can achieve the optimal performance when the obstruction factor is 1/2 and the relative unit length is 0.025.

scholarly journals On the Wake Properties of Segmented Trailing Edge Extensions

2018 ◽  
Author(s):  
Sidaard Gunasekaran ◽  
Daniel Curry
Keyword(s):  
Lift Coefficient ◽  
Free Shear Layer ◽  
Structural Vibrations ◽  
Trailing Edge ◽  
Total Drag ◽  
Image Velocimetry ◽  
Effective Angle ◽  
The University ◽  
Naca 0012 ◽  
Low Speed Wind Tunnel

Changes in the amount and the distribution of mean and turbulent quantities in the free shear layer wake of a 2D NACA 0012 airfoil and AR 4 NACA 0012 wing with passive segmented rigid trailing edge (TE) extensions was investigated at the University of Dayton Low Speed Wind Tunnel (UD-LSWT). The TE extensions were intentionally placed at zero degrees with respect to the chord line to study the effects of segmented extensions without changing the effective angle of attack. Force based experiments was used to determine the total lift coefficient variation of hte wing with seven segmented trailing edge extensions distributed across the span. The segmented trailing edge extensions had negligible effect of lift coefficient but showed measurable decrement in sectional and total drag coefficient. Investigation of turbulent quantities (obtained through Particle Image Velocimetry (PIV)) such as Reynolds stress, streamwise and transverse RMS in the wake, reveal a significant decrease in magnitude when compared to the baseline. The decrease in the magnitude of turbulent parameters was supported by the changes in coherent structures obtained through two-point correlations. Apart from the reduction in drag, the lower turbulent wake generated by the extensions has implications in reducing structural vibrations and acoustic tones.

Elliptic Airfoil Stall Analysis With Trailing Edge Slots

2010 ◽  
Author(s):  
Jonathan Kweder ◽  
Mary Ann Clarke ◽  
James E. Smith
Keyword(s):  
Lift Coefficient ◽  
Leading Edge ◽  
Surface Velocity ◽  
Circulation Control ◽  
West Virginia University ◽  
Trailing Edge ◽  
Near Surface ◽  
Wind Speeds ◽  
Edge Location ◽  
Stall Angle

Circulation control (CC) is a high-lift methodology that can be used on a variety of aerodynamic applications. This technology has been in the research and development phase for over sixty years primarily for fixed wing aircraft where the early models were referred to as “blown flaps”. Circulation control works by increasing the near surface velocity of the airflow over the leading edge and/or trailing edge of a lifting surface This phenomenon keeps the boundary layer jet attached to the wing surface thus increasing the lift generated on the surface. The circulation control airflow adds energy to the lift force through conventional airfoil lift production and by altering the circulation of stream lines around the airfoil. For this study, a 10:1 aspect ratio elliptical airfoil with a chord length of 11.8 inches and a span of 31.5 inches was inserted into the West Virginia University Closed Loop Wind Tunnel and was tested at varying wind speeds (80, 100, and 120 feet per second), angle of attack (zero to sixteen degrees), and blowing coefficients, ranging from 0.0006 to 0.0127 depending on plenum pressure. By comparing the non-circulation controlled wing with the active circulation control data, a trend was found as to the influence of circulation control on the stall characteristics of the wing for trailing edge active control. For this specific case, when the circulation control is in use on the 10:1 elliptical airfoil, the stall angle decreased, from eight degrees to six degrees, while providing a 70% increase in lift coefficient. It should be noted that due to the trailing edge location of the circulation control exit jet, a “virtual” camber is created with the free stream air adding length to the overall airfoil. Due to this phenomena, the actual stall angle measured increased from eight degrees on the un-augmented airfoil, to a maximum of twelve degrees.

Wood Duck (Aix sponsa)

1995 ◽  
Author(s):  
Gary R. Hepp ◽  
Frank C. Bellrose
Keyword(s):  
Aix Sponsa ◽  
Wood Duck

Experimental analysis of cell pattern on grid fin aerodynamics in subsonic flow

2019 ◽  
Vol 234 (3) ◽  
pp. 537-562
Author(s):  
Manish Tripathi ◽  
Mahesh M Sucheendran ◽  
Ajay Misra
Keyword(s):  
Subsonic Flow ◽  
Lift Coefficient ◽  
Aerodynamic Performance ◽  
Aerodynamic Efficiency ◽  
Grid Fin ◽  
Stall Angle ◽  
The Individual ◽  
The Impact ◽  
Control Surfaces

Grid fins consisting of a lattice of high aspect ratio planar members encompassed by an outer frame are unconventional control surfaces used on numerous missiles and bombs due to their enhanced lifting characteristics at high angles of attack and across wider Mach number regimes. The current paper accomplishes and compares the effect of different grid fin patterns on subsonic flow aerodynamics of grid fins by virtue of the determination of their respective aerodynamic forces. Furthermore, this study deliberates the impact of gap variation on aerodynamics of different patterns. Results enunciate enhanced aerodynamic efficiency, and lift slope for web-fin cells and single diamond patterns compared to the baseline model. Moreover, the study indicates improved aerodynamic performance for diamond patterns with higher gaps by providing elevated maximum lift coefficient, delayed stall angle, and comparable drag at lower angles. The study established the presence of an additional effect termed as the inclination effect alongside the cascade effect leading to deviations with respect to lift, stall, and aerodynamic efficiency amongst different gap variants of the individual patterns. Thus, optimization based on the aerodynamic efficiency, stall angle requirements, and construction cost by optimum pattern and gap selection can be carried out through this analysis, which can lead to elevated aerodynamic performance for grid fins.

Effects of leading-edge bevel angle on the aerodynamic forces of a non-slender 50° delta wing

2005 ◽  
Vol 109 (1098) ◽  
pp. 403-407 ◽  
Author(s):  
J. J. Wang ◽  
S. F. Lu
Keyword(s):  
Delta Wing ◽  
Lift Coefficient ◽  
Leading Edge ◽  
Relative Thickness ◽  
Aerodynamic Performances ◽  
Stall Angle ◽  
Drag Ratio ◽  
Low Speed Wind Tunnel ◽  
Lift To Drag Ratio ◽  
Blunt Leading Edge

Abstract The aerodynamic performances of a non-slender 50° delta wing with various leading-edge bevels were measured in a low speed wind tunnel. It is found that the delta wing with leading-edge bevelled leeward can improve the maximum lift coefficient and maximum lift to drag ratio, and the stall angle of the wing is also delayed. In comparison with the blunt leading-edge wing, the increment of maximum lift to drag ratio is 200%, 98% and 100% for the wings with relative thickness t/c = 2%, t/c = 6.7% and t/c = 10%, respectively.

scholarly journals Design and Validation of a New Morphing Camber System by Testing in the Price—Païdoussis Subsonic Wind Tunnel

Aerospace ◽  
2020 ◽  
Vol 7 (3) ◽  
pp. 23 ◽  
Author(s):  
David Communier ◽  
Ruxandra Mihaela Botez ◽  
Tony Wong
Keyword(s):  
Wind Tunnel ◽  
Unmanned Aerial Vehicle ◽  
Lift Coefficient ◽  
Angle Of Attack ◽  
Leading Edge ◽  
Trailing Edge ◽  
Subsonic Wind Tunnel ◽  
Aerial Vehicle ◽  
Stall Angle

This paper presents the design and wind tunnel testing of a morphing camber system and an estimation of performances on an unmanned aerial vehicle. The morphing camber system is a combination of two subsystems: the morphing trailing edge and the morphing leading edge. Results of the present study show that the aerodynamics effects of the two subsystems are combined, without interfering with each other on the wing. The morphing camber system acts only on the lift coefficient at a 0° angle of attack when morphing the trailing edge, and only on the stall angle when morphing the leading edge. The behavior of the aerodynamics performances from the MTE and the MLE should allow individual control of the morphing camber trailing and leading edges. The estimation of the performances of the morphing camber on an unmanned aerial vehicle indicates that the morphing of the camber allows a drag reduction. This result is due to the smaller angle of attack needed for an unmanned aerial vehicle equipped with the morphing camber system than an unmanned aerial vehicle equipped with classical aileron. In the case study, the morphing camber system was found to allow a reduction of the drag when the lift coefficient was higher than 0.48.

Vortex wakes of birds: recent developments using digital particle image velocimetry in a wind tunnel

2006 ◽  
Vol 56 (4) ◽  
pp. 535-549 ◽  
Author(s):  
◽  
◽  
◽  
Keyword(s):  
Particle Image Velocimetry ◽  
Wind Tunnel ◽  
Particle Image ◽  
Lift Coefficient ◽  
Time History ◽  
Digital Particle Image Velocimetry ◽  
Wake Vortices ◽  
Image Velocimetry ◽  
Recent Developments ◽  
Size And Morphology

AbstractA flying animal generates a trail of wake vortices that contain information about the time history and magnitude of aerodynamic forces developed on the wings and body. Methods for visualising and recording wake vortices have been developed, allowing quantitative measurements by digital particle image velocimetry (DPIV). Results from DPIV experiments in a wind tunnel are presented for four passerine species of differing size and morphology. The normalised vorticity and its integrated quantity, circulation (Γ) both decline gradually with increasing flight speed. The measured circulations are successfully explained by a simple aerodynamic model where a normalised circulation, Γ/Uc, represents half the time-averaged lift coefficient, which is >2 at 4 m s−1 for a thrush nightingale.

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