A Leading-Edge Alula-Inspired Device (LEAD) for Stall Mitigation and Lift Enhancement for Low Reynolds Number Finite Wings

2018 ◽  
Author(s):  
Mihary R. Ito ◽  
Chengfang Duan ◽  
Leonardo P. Chamorro ◽  
Aimy A. Wissa
Keyword(s):  
Aspect Ratio ◽  
Flow Separation ◽  
Three Dimensional ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Tip Vortices ◽  
Low Reynolds Numbers ◽  
Lift Enhancement ◽  
Low Reynolds ◽  
Torque Transducer

Even though Unmanned Aerial Vehicles (UAVs) operating at low Reynolds numbers are becoming common, their performance and maneuverability are still greatly limited due to aerodynamic phenomena such as stall and flow separation. Birds mitigate these limitations by adapting their wings and feather shapes during flight. Equipped with a set of small feathers, known as the alula, located near the leading edge and covering 5% to 20% of the span, bird wings can sustain the lift necessary to fly at low velocities and high angles of attack. This paper presents the effect on lift generation of different placements of a Leading-Edge Alula-inpsired Device (LEAD) along the span of a moderate aspect-ratio wing. The device is modeled after the alula on a bird, and it increases the capability of a wing to maintain higher pressure gradients by modifying the near-wall flow close to the leading-edge. It also generates tip vortices that modify the turbulence on the upper-surface of the wing, delaying flow separation. The effect of the LEAD can be compared to traditional slats or vortex generators on two-dimensional wings. For finite wings, on the other hand, the effect depends on the interaction between the LEADs tip vortices and those from the main structure. Wind tunnel experiments were conducted on a cambered wing at post-stall and deep-stall angles of attack at low Reynolds numbers of 100,000 and 135,000. To quantify the aerodynamic effect of the device, the lift generated by the wing with and without the LEAD were measured using a 6-axis force and torque transducer, and the resulting lift coefficients were compared. Results show that the location of the LEAD yielding the highest lift enhancement was 50% semi-span away from the wing root. Lift improvements of up to 32% for post stall and 37% for deep stall were obtained at this location, demonstrating that the three-dimensional effects of the LEAD are important. The lift enhancement was also more prominent on a finite moderate aspect-ratio wing (3D) than on an airfoil (2D), confirming that the LEAD is a three-dimensional device. Identifying the configurations and deployment parameters that improve lift generation the most is needed to design an adaptive LEAD that can be implemented on a UAV wing for increased mission-adaptability.

Experiments on the Velocity Field Around a Low Aspect Ratio Wing at Low Reynolds Numbers

2009 ◽  
Author(s):  
Daniel R. Morse ◽  
James A. Liburdy
Keyword(s):  
Reynolds Number ◽  
Aspect Ratio ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Shear Stresses ◽  
Tip Vortices ◽  
Low Reynolds Numbers ◽  
Low Aspect Ratio ◽  
Low Reynolds ◽  
Wing Tip

The flow structure around a low aspect ratio wing at low Reynolds numbers and a fixed angle of attack of 20° is discussed using flow visualization as well as Three-Component Time-Resolved Particle Image Velocimetry (3C TR PIV). Mean quantities and statistical measurements of velocity were obtained and used to describe the average and transient characteristics of the flow field. Effects of spanwise variation from centerline to wingtip and Reynolds number variation from 1.3×104 to 6.6×104 are discussed. The role of the wing tip vortices is observed to be large in a low aspect ratio wing. The transfer of momentum via Reynolds shear stresses is shown in the leading edge region. Normalized spanwise shear stresses associated with the wing tip vortices are observed to increase with increasing Reynolds number.

Vortex separation and interaction in the wake of inclined trapezoidal plates

2015 ◽  
Vol 771 ◽  
pp. 341-369 ◽  
Author(s):  
Yuqi Huang ◽  
James Venning ◽  
Mark C. Thompson ◽  
John Sheridan
Keyword(s):  
Aspect Ratio ◽  
Strouhal Number ◽  
Angle Of Attack ◽  
Three Dimensional ◽  
Leading Edge ◽  
Reynolds Numbers ◽  
Taper Angle ◽  
Low Reynolds Numbers ◽  
Vortex Loops ◽  
Trailing Edges

Full three-dimensional numerical simulations are employed to investigate the flows over inclined trapezoidal low-aspect-ratio plates at low Reynolds numbers, aiming to understand the unsteadiness induced by the interaction between the trailing vortical wake structures originating from the swept edges, and those from the leading and trailing edges. The flows past eighteen different plate geometries in three broad sets are simulated to study the influence of aspect ratio, taper angle and angle of attack on the wake vortices and the force coefficients. Both taper ratio and angle of attack of plates with the same area are found to have a broadly predictable influence on the wake stability and asymptotic forces. Smaller taper ratios result in lower maximum lift, while an increase in the angle of attack results in a reduction in the differences in maximum lift. Two distinct modes of periodic unsteady flow with significant differences in frequency are observed. The corresponding vortex-shedding mechanisms are analysed with the aid of $Q$-criterion isosurfaces and streamlines. A low wake frequency is observed at small taper angles when there is relative independence between the von Kármán vortices originating from the leading and trailing edges, and weak swept-edge vortices. The dominant Strouhal number in this state is approximately 0.09. When the taper angle or angle of attack increases, the flows over the swept edges form stronger trailing vortex structures which interact strongly with the leading-edge vortices, combining to produce a regular stream of vortex loops shed into the wake. In this regime, the dominant Strouhal number increases to approximately 0.14–0.18. Higher Reynolds numbers and/or angles of attack result in a loss of centre plane reflection symmetry in the wake. The aerodynamic forces have been quantified as a function of the problem parameters and plate geometry.

Investigation on the effect of leading edge tubercles of sweptback wing at low reynolds number

2020 ◽  
Vol 21 (6) ◽  
pp. 621
Author(s):  
Veerapathiran Thangaraj Gopinathan ◽  
John Bruce Ralphin Rose ◽  
Mohanram Surya
Keyword(s):  
Leading Edge ◽  
Reynolds Numbers ◽  
Sweep Angle ◽  
Laminar Separation ◽  
Low Reynolds Numbers ◽  
Flow Energy ◽  
Airplane Wing ◽  
Low Reynolds ◽  
Naca 0015 ◽  
Wing Performance

Aerodynamic efficiency of an airplane wing can be improved either by increasing its lift generation tendency or by reducing the drag. Recently, Bio-inspired designs have been received greater attention for the geometric modifications of airplane wings. One of the bio-inspired designs contains sinusoidal Humpback Whale (HW) tubercles, i.e., protuberances exist at the wing leading edge (LE). The tubercles have excellent flow control characteristics at low Reynolds numbers. The present work describes about the effect of tubercles on swept back wing performance at various Angle of Attack (AoA). NACA 0015 and NACA 4415 airfoils are used for swept back wing design with sweep angle about 30°. The modified wings (HUMP 0015 A, HUMP 0015 B, HUMP 4415 A, HUMP 4415 B) are designed with two amplitude to wavelength ratios (η) of 0.1 & 0.24 for the performance analysis. It is a novel effort to analyze the tubercle vortices along the span that induce additional flow energy especially, behind the tubercles peak and trough region. Subsequently, Co-efficient of Lift (CL), Co-efficient of Drag (CD) and boundary layer pressure gradients also predicted for modified and baseline (smooth LE) models in the pre & post-stall regimes. It was observed that the tubercles increase the performance of swept back wings by the enhanced CL/CD ratio in the pre-stall AoA region. Interestingly, the flow separation region behind the centerline of tubercles and formation of Laminar Separation Bubbles (LSB) were asymmetric because of the sweep.

The influence of the flow separation bubble and transition location on the profile drag of three 4-digit NACA aerofoil profiles

2021 ◽  
pp. 0309524X2110550
Author(s):  
Moutaz Elgammi ◽  
Tonio Sant ◽  
Atiyah Abdulmajid Ateeah
Keyword(s):  
Wind Tunnel ◽  
Flow Separation ◽  
Separation Bubble ◽  
Reynolds Numbers ◽  
Force Balance ◽  
Navier Stokes ◽  
Separation Mechanism ◽  
Numerical Work ◽  
Low Reynolds Numbers ◽  
Low Reynolds

Modeling of the flow over aerofoil profiles at low Reynolds numbers is difficult due to the complex physics associated with the laminar flow separation mechanism. Two major problems arise in the estimation of profile drag: (1) the drag force at low Reynolds numbers is extremely small to be measured in a wind tunnel by force balance techniques, (2) the profile drag is usually calculated by pressure integration, hence the skin friction component of drag is excluded. In the present work, three different 4-digit NACA aerofoils are investigated. Measurements are conducted in an open-ended subsonic wind tunnel, while numerical work is performed by time Reynolds-averaged Navier Stokes (RANS) coupled with the laminar-kinetic-energy ( K-kl-w) turbulence model. The influence of the flow separation bubbles and transition locations on the profile drag is discussed and addressed. This paper gives important insights into importance of measurements at low Reynolds numbers for better aerodynamic loads predictions.

scholarly journals Three-dimensional wake transition in the flow over four square cylinders at low Reynolds numbers

AIP Advances ◽  
2020 ◽  
Vol 10 (1) ◽  
pp. 015142
Author(s):  
Yuhang Zhang ◽  
Rui Wang ◽  
Yaoran Chen ◽  
Yan Bao ◽  
Zhaolong Han ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Reynolds Numbers ◽  
Low Reynolds Numbers ◽  
Square Cylinders ◽  
Low Reynolds ◽  
Four Square ◽  
Wake Transition
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