Flow Structure Above Stationary and Oscillating Low-Aspect-Ratio Wing

2012 ◽  
Author(s):  
Miguel R. Visbal ◽  
Daniel J. Garmann
Keyword(s):  
Reynolds Number ◽  
Aspect Ratio ◽  
Flow Structure ◽  
Large Scale ◽  
Lift Coefficient ◽  
Pressure Fluctuations ◽  
Leading Edge ◽  
Tip Vortex ◽  
Eddy Simulation ◽  
Moderate Reynolds Number

Computations have been carried out in order to describe the complex unsteady flow structure over a stationary and plunging aspect-ratio-two wing under low Reynolds number conditions (Rec = 104). The flow fields are computed employing a high-fidelity implicit large-eddy simulation (ILES) approach found to be effective for moderate Reynolds number flows exhibiting mixed laminar, transitional and turbulent regions. The evolution of the flow structure and aerodynamic loading as a function of increasing angle of attack is presented. Lift and pressure fluctuations are found to be primarily dominated by the large scale circulatory pattern established above the wing due to separation from the leading edge, and by the inherent three dimensionality of the flow induced by the finite aspect ratio. The spanwise distribution of the sectional lift coefficient revealed only a minor direct contribution to the loading exherted by the tip vortex. High-frequency, small-amplitude oscillations are shown to have a significant effect on the separation process and accompanying loads suggesting potential flow control through either suitable actuation or aero-elastic tailoring.

Flow structure on a simultaneously pitching and rotating wing

2014 ◽  
Vol 756 ◽  
pp. 354-383 ◽  
Author(s):  
M. Bross ◽  
D. Rockwell
Keyword(s):  
Flow Structure ◽  
Large Scale ◽  
Three Dimensional ◽  
Leading Edge ◽  
Tip Vortex ◽  
Pure Rotation ◽  
Large Scale Vortex ◽  
Edge Vortex ◽  
Vorticity Flux ◽  
Rotating Wing

AbstractA technique of particle image velocimetry is employed to characterize the three-dimensional flow structure on a wing subjected to simultaneous pitch-up and rotational motions. Distinctive vortical structures arise, relative to the well-known patterns on a wing undergoing either pure pitch-up or pure rotation. The features associated with these simultaneous motions include: stabilization of the large-scale vortex generated at the leading edge, which, for pure pitch-up motion, rapidly departs from the leading-edge region; preservation of the coherent vortex system involving both the tip vortex and the leading-edge vortex (LEV), which is severely degraded for pure rotational motion; and rapid relaxation of the flow structure upon termination of the pitch-up component, whereby the relaxed flow converges to a similar state irrespective of the pitch rate. Three-dimensional surfaces of iso-$\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}{Q}$and helicity are employed in conjunction with sectional representations of spanwise vorticity, velocity and vorticity flux to interpret the flow physics.

Analysis of Vortical Flow Field in a Propeller Fan by LDV Measurements and LES—Part II: Unsteady Nature of Vortical Flow Structures Due to Tip Vortex Breakdown

2001 ◽  
Vol 123 (4) ◽  
pp. 755-761 ◽  
Author(s):  
Choon-Man Jang ◽  
Masato Furukawa ◽  
Masahiro Inoue
Keyword(s):  
Vortex Breakdown ◽  
Pressure Fluctuations ◽  
Leading Edge ◽  
Vortex Structures ◽  
Tip Vortex ◽  
Vortical Flow ◽  
Small Scale ◽  
Pressure Surface ◽  
Eddy Simulation ◽  
Cyclic Movements

The unsteady nature of vortex structures has been investigated by a large eddy simulation (LES) in a propeller fan with a shroud covering only the rear region of its rotor tip. The simulation shows that the tip vortex plays a major role in the structure and unsteady behavior of the vortical flow in the propeller fan. The spiral-type breakdown of the tip vortex occurs near the midpitch, leading to significant changes in the nature of the tip vortex. The breakdown gives rise to large and cyclic movements of the tip vortex, so that the vortex impinges cyclically on the pressure surface of the adjacent blade. The movements of the tip vortex cause the leading edge separation vortex to oscillate in a cycle, but on a small scale. The movements of the vortex structures induce high-pressure fluctuations on the rotor blade and in the blade passage.

Alula-Inspired Leading Edge Device for Low Reynolds Number Flight

2016 ◽  
Author(s):  
Boris A. Mandadzhiev ◽  
Michael K. Lynch ◽  
Leonardo P. Chamorro ◽  
Aimy A. Wissa
Keyword(s):  
Reynolds Number ◽  
Wind Tunnel ◽  
Drag Coefficient ◽  
Lift Coefficient ◽  
Angle Of Attack ◽  
Leading Edge ◽  
Aerodynamic Performance ◽  
Tip Vortex ◽  
Relative Angle ◽  
Lift And Drag

Robust and predictable aerodynamic performance of unmanned aerial vehicles at the limits of their design envelope is critical for safety and mission adaptability. In order for a fixed wing aircraft to maintain the lift necessary for sustained flight at very low speeds and large angles of attack (AoA), the wing shape has to change. This is often achieved by using deployable aerodynamic surfaces, such as flaps or slats, from the wing leading or trailing edges. In nature, one such device is a feathered structure on birds’ wings called the alula. The span of the alula is 5% to 20% of the wing and is attached to the first digit of the wing. The goal of the current study is to understand the aerodynamic effects of the alula on wing performance. A series of wind tunnel experiments are performed to quantify the effect of various alula deployment parameters on the aerodynamic performance of a cambered airfoil (S1223). A full wind tunnel span wing, with a single alula located at the wing mid-span is tested under uniform low-turbulence flow at three Reynolds numbers, Re = 85,000, 106,00 and 146,000. An experimental matrix is developed to find the range of effectiveness of an alula-type device. The alula relative angle of attack measured measured from the mean chord of the airfoil is varied to modulate tip-vortex strength, while the alula deflection is varied to modulate the distance of the tip vortex to the wing surface. Lift and drag forces were measured using a six axis force transducer. The lift and drag coefficients showed the greatest sensitivity to the the alula relative angle of attack, increasing the normalized lift coefficient by as much as 80%. Improvements in lift are strongly correlated to higher alula angle, with β = 0° – 5°, while reduction in the drag coefficient is observed with higher alula tip deflection ratios and lower β angles. Results show that, as the wing angle of attack and Reynolds number are increased, the overall lift co-efficient improvement is diminished while the reduction in drag coefficient is higher.

Aspect-ratio effects on rotating wings: circulation and forces

2015 ◽  
Vol 767 ◽  
pp. 497-525 ◽  
Author(s):  
Zakery R. Carr ◽  
Adam C. DeVoria ◽  
Matthew J. Ringuette
Keyword(s):  
Aspect Ratio ◽  
Lift Force ◽  
Slow Growth ◽  
Lift Coefficient ◽  
Leading Edge ◽  
Tip Vortex ◽  
Trailing Edge ◽  
Data Set ◽  
Edge Vortex ◽  
Total Circulation

AbstractWe employ experiments to study aspect ratio ($\def\AR{A\mkern-8muR}\AR$) effects on the vortex structure, circulation and lift force for flat-plate wings rotating from rest at 45° angle of attack, which represents a simplified hovering-wing half-stroke. We use the time-varying, volumetric $\AR =2$ data of Carr et al. (Exp. Fluids, vol. 54, 2013, pp. 1–26), reconstructed from phase-locked, phase-averaged stereoscopic digital particle image velocimetry (S-DPIV), and an $\AR =4$ volumetric data set matching the span-based Reynolds number ($\mathit{Re}$) of $\AR =2$. For $\AR =1{-}4$ and $\mathit{Re}_{\mathit{span}}$ of $O$($10^{3}$–$10^{4}$), we directly measure the lift force. The total leading-edge-region circulation for $\AR =2$ and 4 compares best overall using a span-based normalization and for matching rotation angles. The total circulation increases across the span to the tip region, and is larger for $\AR =2$. After the startup, the total circulation for each $\AR$ has a similar slope and a slow growth. The first leading-edge vortex (LEV) and the tip vortex (TV) for $\AR =4$ move past the trailing edge, followed by substantial breakdown. For $\AR =2$ the outboard, aft-tilted LEV merges with the TV and resides over the tip, although breakdown also occurs. Where the LEV is ‘stable’ inboard, its circulation saturates for $\AR =2$ and the growth slows for $\AR =4$. Aft LEV tilting reduces the spanwise LEV circulation for each $\AR$. Both positive and negative axial flow are found in the first LEV for $\AR =2$ and 4, with the positive component being somewhat larger. This yields a generally positive (outboard) average vorticity flux. The average lift coefficient is essentially constant with $\AR$ from 1 to 4 during the slow growth phase, although the large-time behaviour shows a slight decrease in lift coefficient with increasing $\AR$. The S-DPIV data are used to obtain the lift impulse and the spanwise and streamwise components contributing to the lift coefficient. The spanwise contribution is similar for $\AR =2$ and 4, due to similar trailing-edge vortex interactions, LEV saturation behaviour and total circulation slopes. However, for $\AR =2$ the streamwise contribution is much larger, because of the stronger, coherent TV and aft-tilted LEV, which will create a relatively lower-pressure region over the tip.

Computations of Flow Structure and Heat Transfer in a Dimpled Channel at Low to Moderate Reynolds Number

2004 ◽  
Author(s):  
Wilfred V. Patrick ◽  
Danesh K. Tafti
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Flow Structure ◽  
Large Scale ◽  
Channel Height ◽  
Turbulent Regime ◽  
Laminar Regime ◽  
Flux Boundary Condition ◽  
Flow And Heat Transfer ◽  
Moderate Reynolds Number

Time-accurate calculations are used to investigate the three-dimensional flow structure and understand its influence on the heat transfer in a channel with concave indentations on one wall. A dimple depth to channel height ratio of 0.4 and dimple depth to imprint diameter ratio of 0.2 is used in the calculations. The Reynolds number (based on channel height) varies from Re = 280 in the laminar regime to Re = 2000 in the early turbulent regime. Fully developed flow and heat transfer conditions were assumed and a constant heat flux boundary condition was applied to the walls of the channel. In the laminar regime, the flow and heat transfer characteristics are dominated by the recirculation zones in the dimple with resulting augmentation ratios below unity. Flow transition is found to occur between Re = 1020 and 1130 after which both heat transfer and friction augmentation increase to values of 3.22 and 2.75, respectively, at Re = 2000. The presence of large scale vortical structures ejected from the dimple cavity dominate all aspects of the flow and heat transfer, not only on the dimpled surface but also on the smooth wall. In all cases the thermal efficiency using dimples was found to be significantly larger than other heat transfer augmentation techniques currently employed.

Uncoupling the effects of aspect ratio, Reynolds number and Rossby number on a rotating insect-wing planform

2018 ◽  
Vol 859 ◽  
pp. 921-948 ◽  
Author(s):  
Shantanu S. Bhat ◽  
Jisheng Zhao ◽  
John Sheridan ◽  
Kerry Hourigan ◽  
Mark C. Thompson
Keyword(s):  
Reynolds Number ◽  
Aspect Ratio ◽  
Large Scale ◽  
Stokes Equations ◽  
Rotation Axis ◽  
Leading Edge ◽  
Rossby Number ◽  
Insect Wing ◽  
Wide Range ◽  
The Individual

The individual and combined influences of aspect ratio ($A$), Reynolds number ($Re$) and Rossby number ($Ro$) on the leading-edge vortex (LEV) of a rotating wing of insect-like planform are investigated numerically. A previous study from our group has determined the wingspan to be an appropriate length scale governing the large-scale LEV structure. In this study, the $A$ range considered is further extended, to show that this scaling works well as $A$ is varied by a factor of 4 ($1.8\leqslant A\leqslant 7.28$) and over a $Re$ range of two orders of magnitude. The present study also extends this scaling for wings with an offset from the rotation axis, which is typically the case for actual insects and often for experiments. Remarkably, the optimum range of $A$ based on the lift coefficients at different $Re$ coincides with that observed in nature. The scaling based on the wingspan is extended to the acceleration terms of the Navier–Stokes equations, suggesting a modified scaling of $Ro$, which decouples the effects of $A$. A detailed investigation of the flow structures, by increasing $Ro$ in a wide range, reveals the weakening of the LEV due to the reduced spanwise flow, resulting in a reduced lift. Overall, the use of span-based scaling of $Re$ and $Ro$, together with $A$, may help reconcile apparent conflicting trends between observed variations in aerodynamic performance in different sets of experiments and simulations.

scholarly journals Optimizing Effect of Wavy Leading Edge (WLE) in Rectangular Wing and Taper Wing

2021 ◽  
Vol 1 (2) ◽  
pp. 56-68
Author(s):  
Iis Rohmawati ◽  
Hiroshi Arai ◽  
Hidemi Mutsuda ◽  
Takuji Nakashima ◽  
Rizal Mahmud
Keyword(s):  
Reynolds Number ◽  
Aspect Ratio ◽  
Lift Coefficient ◽  
Leading Edge ◽  
Wing Shape ◽  
Aspect Ratios ◽  
Impressive Result ◽  
Rectangular Form ◽  
Numerical Research ◽  
Wing Aspect Ratio

Experimental and numerical research have been performed to investigate the Wavy Leading Edge (WLE) effect on the rectangular wing. The WLE is inspired by humpback whale flipper morphology which is blunt and rounded in certain form pattern. This flipper shape plays an important role for its behaviour specially capturing their prey. This advantage could be applied to other systems such as fin stabilizers or wind turbines. Steady cases in various aspect ratios were conducted to find out the optimum effect of WLE with baseline NACA 0018 profile at Reynolds number 1.4 x 105. The chord length of the wing (c) was 125 mm. The WLE shape defined as wavelength (W) 8% of c and amplitude (d) is 5% of c. The aspect ratio (AR) variations were 1.6; 3.9; 5.1; 7.9 and 9.6.  A simple rectangular form of the wing was selected to analysis the WLE effect on the various ARs. The taper wing shape is applied to find out the WLE effect at the AR 7.9. three types of taper ratio (TR) are 0.1; 0.3 and 0.5. The results show that the WLE on the taper wing has better advantage to control the stall in steady case. Another impressive result was the WLE wing with AR 7.9 and TR 0.3 has the best lift coefficient and pressure distribution.Keywords: stall, wavy leading edge, steady case, rectangle wing, taper wing, aspect ratio. 

A time-domain analysis of the large-scale flow structure in a circular jet. Part 1. Moderate Reynolds number

1977 ◽  
Vol 83 (4) ◽  
pp. 641-671 ◽  
Author(s):  
H. H. Bruun
Keyword(s):  
Reynolds Number ◽  
Flow Structure ◽  
Time Domain ◽  
Large Scale ◽  
Time Domain Analysis ◽  
Large Scale Structure ◽  
Scale Structure ◽  
Moderate Reynolds Number ◽  
Temporal And Spatial ◽  
Large Scale Flow

This paper presents a new experimental time-domain technique for the evaluation of the large-scale structure in a turbulent flow. The technique is demonstrated by hot-wire anemometry for a circular jet flow at a moderate Reynolds number of 104, and the large-scale structure identified is compared successfully with smoke flow-visualization observations. The temporal and spatial relationships of the separate large-scale flow events have been derived, and this information enabled the evaluation of the nonlinear spatial development of the large-scale flow structure.

Numerical Investigation of Intermittent Corner Separation in a Linear Compressor Cascade

2016 ◽  
Author(s):  
Wei Ma ◽  
Feng Gao ◽  
Xavier Ottavy ◽  
Lipeng Lu ◽  
A. J. Wang
Keyword(s):  
Flow Field ◽  
Large Scale ◽  
Leading Edge ◽  
Suction Side ◽  
Detached Eddy Simulation ◽  
Compressor Cascade ◽  
Linear Compressor ◽  
Corner Separation ◽  
Eddy Simulation ◽  
Linear Compressor Cascade

Recently bimodal phenomenon in corner separation has been found by Ma et al. (Experiments in Fluids, 2013, doi:10.1007/s00348-013-1546-y). Through detailed and accurate experimental results of the velocity flow field in a linear compressor cascade, they discovered two aperiodic modes exist in the corner separation of the compressor cascade. This phenomenon reflects the flow in corner separation is high intermittent, and large-scale coherent structures corresponding to two modes exist in the flow field of corner separation. However the generation mechanism of the bimodal phenomenon in corner separation is still unclear and thus needs to be studied further. In order to obtain instantaneous flow field with different unsteadiness and thus to analyse the mechanisms of bimodal phenomenon in corner separation, in this paper detached-eddy simulation (DES) is used to simulate the flow field in the linear compressor cascade where bimodal phenomenon has been found in previous experiment. DES in this paper successfully captures the bimodal phenomenon in the linear compressor cascade found in experiment, including the locations of bimodal points and the development of bimodal points along a line that normal to the blade suction side. We infer that the bimodal phenomenon in the corner separation is induced by the strong interaction between the following two facts. The first is the unsteady upstream flow nearby the leading edge whose angle and magnitude fluctuate simultaneously and significantly. The second is the high unsteady separation in the corner region.

Pressure and velocity measurements of an incompressible moderate Reynolds number jet interacting with a tangential flat plate

2015 ◽  
Vol 770 ◽  
pp. 247-272 ◽  
Author(s):  
A. Di Marco ◽  
M. Mancinelli ◽  
R. Camussi
Keyword(s):  
Reynolds Number ◽  
Flat Plate ◽  
Scaling Laws ◽  
Pressure Fluctuations ◽  
Wall Pressure ◽  
Theoretical Modelling ◽  
Wall Pressure Fluctuations ◽  
Moderate Reynolds Number ◽  
The Mean ◽  
Pressure And Velocity Measurements

The statistical properties of wall pressure fluctuations generated on a rigid flat plate by a tangential incompressible single stream jet are investigated experimentally. The study is carried out at moderate Reynolds number and for different distances between the nozzle axis and the flat plate. The overall aerodynamic behaviour is described through hot wire anemometer measurements, providing the effect of the plate on the mean and fluctuating velocity. The pressure field acting on the flat plate was measured by cavity-mounted microphones, providing point-wise pressure signals in the stream-wise and span-wise directions. Statistics of the wall pressure fluctuations are determined in terms of time-domain and Fourier-domain quantities and a parametric analysis is conducted in terms of the main geometrical length scales. Possible scaling laws of auto-spectra and coherence functions are presented and implications for theoretical modelling are discussed.

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