3D Effects in the Wake Vortex Formation of an Elliptic Flat Plate in Hover

2017 ◽  
Author(s):  
Vivek Nair ◽  
Siddarth Chintamani ◽  
B. H. Dennis
Keyword(s):  
Flat Plate ◽  
Vortex Formation ◽  
Three Dimensional ◽  
Leading Edge ◽  
Leading Edge Vortex ◽  
Elliptic Geometry ◽  
3D Effects ◽  
Edge Vortex ◽  
Formation Number ◽  
Vorticity Transport

A Numerical Analysis is conducted to investigate the Leading Edge Vortex (LEV) dynamics of an elliptic flat plate undergoing 2 dimensional symmetric flapping motion in hover. The plate is modeled with an aspect ratio of 3 and a flapping trajectory resulting in Reynolds number 225 is studied. The leading edge vortex stability is analyzed as a function of the non dimensional formation number and a vorticity transport analysis is carried to understand the flux budgets present. The LEV formation number is found to be 2.6. The results of vorticity analysis show the highly three dimensional nature of the LEV growth for an elliptic geometry.

Optimal Leading Edge Vortex Formation of a Flapping Foil in Energy Harvesting Regime

2017 ◽  
Author(s):  
Firas F. Siala ◽  
Alexander D. Totpal ◽  
James A. Liburdy
Keyword(s):  
Energy Harvesting ◽  
Vortex Formation ◽  
Leading Edge ◽  
Flux Analysis ◽  
Leading Edge Vortex ◽  
Flapping Foil ◽  
Flow Energy ◽  
Edge Vortex ◽  
Formation Number ◽  
Harvesting Regime

An experimental investigation is conducted to study the leading edge vortex (LEV) evolution of a simultaneously heaving and pitching foil operating in the energy harvesting regime. Two dimensional particle image velocimetry measurements are collected in a wind tunnel at reduced frequencies of k = fc/U = 0.05–0.20. Vorticity flux analysis is performed to calculate the constant C in the vortex formation number equation proposed by J. O. Dabiri [1], and it is shown that for a flapping foil operating in the energy harvesting regime, this constant is approximately equal to 1.33. We demonstrate that the optimal LEV formation number (T̂max ≈ 4) is achieved at k = 0.11, which is well within the range of optimal reduced frequency for energy harvesting applications (k = 0.1–0.15). This suggests that the flow energy extraction is closely related to the efficient evolution process of the LEV.

Vortex formation and shedding from a cyber-physical pitching plate

2016 ◽  
Vol 793 ◽  
pp. 229-247 ◽  
Author(s):  
Kyohei Onoue ◽  
Kenneth S. Breuer
Keyword(s):  
Flat Plate ◽  
Physical System ◽  
Vortex Formation ◽  
Leading Edge ◽  
Cyber Physical System ◽  
Leading Edge Vortex ◽  
Unsteady Aerodynamic ◽  
Wide Range ◽  
Edge Vortex ◽  
Aerodynamic Torque

We report on the dynamics of the formation and growth of the leading-edge vortex and the corresponding unsteady aerodynamic torque induced by large-scale flow-induced oscillations of an elastically mounted flat plate. All experiments are performed using a high-bandwidth cyber-physical system, which enables the user to access a wide range of structural dynamics using a feedback control system. A series of two-dimensional particle image velocimetry measurements are carried out to characterize the behaviour of the separated flow structures and its relation to the plate kinematics and unsteady aerodynamic torque generation. By modulating the structural properties of the cyber-physical system, we systematically analyse the formation, strength and separation of the leading-edge vortex, and the dependence on kinematic parameters. We demonstrate that the leading-edge vortex growth and strength scale with the characteristic feeding shear-layer velocity and that a potential flow model using the measured vortex circulation and position can, when coupled with the steady moment of the flat plate, accurately predict the net aerodynamic torque on the plate. Connections to previous results on optimal vortex formation time are also discussed.

Vorticity transport in the leading-edge vortex on a rotating blade

2014 ◽  
Vol 743 ◽  
pp. 249-261 ◽  
Author(s):  
Craig J. Wojcik ◽  
James H. J. Buchholz
Keyword(s):  
Leading Edge ◽  
Quasi Equilibrium ◽  
Transport Mechanisms ◽  
Leading Edge Vortex ◽  
Rotating Blade ◽  
Edge Vortex ◽  
Rotation Motion ◽  
Vorticity Transport ◽  
Control Volumes ◽  
Quiescent Fluid

AbstractVorticity transport is analysed within the leading-edge vortex generated on a rectangular flat plate of aspect ratio 4 undergoing a starting rotation motion in a quiescent fluid. Two analyses are conducted on the inboard half of the blade to better understand the vorticity transport mechanisms responsible for maintaining the quasi-equilibrium state of the leading-edge vortex. An initial global analysis between the $25$ and $50\, \%$ spanwise positions suggests that, although spanwise velocity is significant, spanwise convection of vorticity is insufficient to balance the flux of vorticity from the leading-edge shear layer. Subsequent detailed analyses of vorticity transport in planar control volumes at the $25$ and $50\, \%$ spanwise positions verify this conclusion and demonstrate that vorticity annihilation due to interaction between the leading-edge vortex and the opposite-sign layer on the plate surface is an important, often dominant, mechanism for regulation of leading-edge-vortex circulation. Thus, it provides an important condition for maintenance of an attached leading-edge vortex on the inboard portion of the blade.

scholarly journals Video: Leading edge vortex formation in aquatic swimming

2014 ◽  
Author(s):  
Mohsen Daghooghi ◽  
Richard G. Bottom ◽  
Iman Borazjani
Keyword(s):  
Vortex Formation ◽  
Leading Edge ◽  
Leading Edge Vortex ◽  
Edge Vortex

Initiation of Leading-Edge-Vortex Formation on Finite Wings in Unsteady Flow

2015 ◽  
Author(s):  
Yoshikazu Hirato ◽  
Minao Shen ◽  
Sachin Aggarwal ◽  
Ashok Gopalarathnam ◽  
Jack R. Edwards
Keyword(s):  
Unsteady Flow ◽  
Vortex Formation ◽  
Leading Edge ◽  
Leading Edge Vortex ◽  
Edge Vortex

scholarly journals The leading-edge vortex on a rotating wing changes markedly beyond a certain central body size

2018 ◽  
Vol 5 (7) ◽  
pp. 172197 ◽  
Author(s):  
Shantanu S. Bhat ◽  
Jisheng Zhao ◽  
John Sheridan ◽  
Kerry Hourigan ◽  
Mark C. Thompson
Keyword(s):  
Reynolds Number ◽  
Body Size ◽  
Central Body ◽  
Three Dimensional ◽  
Leading Edge ◽  
Particle Image Velocimetry Technique ◽  
Leading Edge Vortex ◽  
Rapid Acquisition ◽  
Edge Vortex ◽  
Rotating Wing

Stable attachment of a leading-edge vortex (LEV) plays a key role in generating the high lift on rotating wings with a central body. The central body size can affect the LEV structure broadly in two ways. First, an overall change in the size changes the Reynolds number, which is known to have an influence on the LEV structure. Second, it may affect the Coriolis acceleration acting across the wing, depending on the wing-offset from the axis of rotation. To investigate this, the effects of Reynolds number and the wing-offset are independently studied for a rotating wing. The three-dimensional LEV structure is mapped using a scanning particle image velocimetry technique. The rapid acquisition of images and their correlation are carefully validated. The results presented in this paper show that the LEV structure changes mainly with the Reynolds number. The LEV-split is found to be only minimally affected by changing the central body radius in the range of small offsets, which interestingly includes the range for most insects. However, beyond this small offset range, the LEV-split is found to change dramatically.

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