A leading-edge vortex initiation criteria for large amplitude foil oscillations using a discrete vortex model

2021 ◽  
Vol 33 (11) ◽  
pp. 115123
Author(s):  
Kiana Kamrani Fard ◽  
Vickie Ngo ◽  
James A. Liburdy
Keyword(s):  
Large Amplitude ◽  
Leading Edge ◽  
Discrete Vortex ◽  
Leading Edge Vortex ◽  
Vortex Model ◽  
Edge Vortex ◽  
Discrete Vortex Model

Discrete-vortex method with novel shedding criterion for unsteady aerofoil flows with intermittent leading-edge vortex shedding

2014 ◽  
Vol 751 ◽  
pp. 500-538 ◽  
Author(s):  
Kiran Ramesh ◽  
Ashok Gopalarathnam ◽  
Kenneth Granlund ◽  
Michael V. Ol ◽  
Jack R. Edwards
Keyword(s):  
Vortex Shedding ◽  
Leading Edge ◽  
Vortex Method ◽  
Critical Value ◽  
Empirical Parameter ◽  
Discrete Vortex ◽  
Suction Parameter ◽  
Leading Edge Vortex ◽  
Edge Vortex ◽  
Leading Edges

AbstractUnsteady aerofoil flows are often characterized by leading-edge vortex (LEV) shedding. While experiments and high-order computations have contributed to our understanding of these flows, fast low-order methods are needed for engineering tasks. Classical unsteady aerofoil theories are limited to small amplitudes and attached leading-edge flows. Discrete-vortex methods that model vortex shedding from leading edges assume continuous shedding, valid only for sharp leading edges, or shedding governed by ad-hoc criteria such as a critical angle of attack, valid only for a restricted set of kinematics. We present a criterion for intermittent vortex shedding from rounded leading edges that is governed by a maximum allowable leading-edge suction. We show that, when using unsteady thin aerofoil theory, this leading-edge suction parameter (LESP) is related to the $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}A_0$ term in the Fourier series representing the chordwise variation of bound vorticity. Furthermore, for any aerofoil and Reynolds number, there is a critical value of the LESP, which is independent of the motion kinematics. When the instantaneous LESP value exceeds the critical value, vortex shedding occurs at the leading edge. We have augmented a discrete-time, arbitrary-motion, unsteady thin aerofoil theory with discrete-vortex shedding from the leading edge governed by the instantaneous LESP. Thus, the use of a single empirical parameter, the critical-LESP value, allows us to determine the onset, growth, and termination of LEVs. We show, by comparison with experimental and computational results for several aerofoils, motions and Reynolds numbers, that this computationally inexpensive method is successful in predicting the complex flows and forces resulting from intermittent LEV shedding, thus validating the LESP concept.

Discrete Vortex Modeling of a Flapping Foil Energy Harvester With LEV Shedding Criterion

2020 ◽  
Author(s):  
Kiana Kamrani Fard ◽  
James A. Liburdy
Keyword(s):  
Energy Harvesting ◽  
Leading Edge ◽  
Cfd Simulations ◽  
Trailing Edge ◽  
Discrete Vortex ◽  
Suction Parameter ◽  
Vortex Model ◽  
Reduced Frequency ◽  
Overall Efficiency ◽  
Discrete Vortex Model

Abstract The energy harvesting performance of a flapping airfoil is studied through discrete vortex model. Results are obtained for a thin flat airfoil that undergoes a sinusoidal flapping motion for reduced frequencies of k = fC/U∞ = 0.06–0.16 where f is the heaving frequency of the foil, C is the chord length and U∞ is the freestream velocity. The airfoil pitches about the mid-chord and the heaving and pitching amplitudes of the airfoil are h0 = 0.5C and θ0 = 70° respectively, as these numbers have been shown to give optimal energy harvesting results for a rigid airfoil. The study applies a panel-based discrete vortex model that incorporates a leading edge suction parameter criterion to understand the flow behavior around the airfoil. The leading edge suction parameter is found from 2D CFD simulations (Navier-Stokes equations solved in Fluent) for all K values. A correlation between the critical leading edge suction parameter and reduced frequency is found from the identified critical LESP values. An empirical trailing edge separation correction is also applied to the transient force results since flow separation at the trailing edge is anticipated. The parameters of interest from the model are transient distributions of force, power output, and overall efficiency. Model results are then validated against 2D CFD simulations. The effect of reduced frequency on power production and overall efficiency is finally studied to identify the optimal reduced frequency for energy harvesting applications.

Modulation of the Leading-Edge Vortex Shedding Rate in Discrete-Vortex Methods

2022 ◽  
Author(s):  
Alfonso Martínez ◽  
Guosheng He ◽  
Karen Mulleners ◽  
Kiran Kumar Ramesh
Keyword(s):  
Vortex Shedding ◽  
Leading Edge ◽  
Vortex Methods ◽  
Discrete Vortex ◽  
Leading Edge Vortex ◽  
Edge Vortex

Flight

2018 ◽  
Author(s):  
Anders Hedenström
Keyword(s):  
Bird Species ◽  
Leading Edge ◽  
Micro Air Vehicles ◽  
Leading Edge Vortex ◽  
Confined Spaces ◽  
Unsteady Aerodynamic ◽  
Maneuvering Flight ◽  
Edge Vortex ◽  
Lifting Surfaces ◽  
Animal Flight

Animal flight represents a great challenge and model for biomimetic design efforts. Powered flight at low speeds requires not only appropriate lifting surfaces (wings) and actuator (engine), but also an advanced sensory control system to allow maneuvering in confined spaces, and take-off and landing. Millions of years of evolutionary tinkering has resulted in modern birds and bats, which are achieve controlled maneuvering flight as well as hovering and cruising flight with trans-continental non-stop migratory flights enduring several days in some bird species. Unsteady aerodynamic mechanisms allows for hovering and slow flight in insects, birds and bats, such as for example the delayed stall with a leading edge vortex used to enhance lift at slows speeds. By studying animal flight with the aim of mimicking key adaptations allowing flight as found in animals, engineers will be able to design micro air vehicles of similar capacities.

Flow criticality governs leading-edge-vortex initiation on finite wings in unsteady flow

2021 ◽  
Vol 910 ◽  
Author(s):  
Yoshikazu Hirato ◽  
Minao Shen ◽  
Ashok Gopalarathnam ◽  
Jack R. Edwards
Keyword(s):  
Unsteady Flow ◽  
Leading Edge ◽  
Leading Edge Vortex ◽  
Edge Vortex

Abstract

A numerical study of vortex interaction

1984 ◽  
Vol 146 ◽  
pp. 331-345 ◽  
Author(s):  
I. G. Bromilow ◽  
R. R. Clements
Keyword(s):  
Flow Visualization ◽  
Numerical Study ◽  
Experimental Studies ◽  
Shear Layers ◽  
Controlled Study ◽  
Vortex Interaction ◽  
Flow Conditions ◽  
Discrete Vortex ◽  
Vortex Model ◽  
Discrete Vortex Model

Flow visualization has shown that the interaction of line vortices is a combination of tearing, elongation and rotation, the extent of each depending upon the flow conditions. A discrete-vortex model is used to study the interaction of two and three growing line vortices of different strengths and to assess the suitability of the method for such simulation.Many of the features observed in experimental studies of shear layers are reproduced. The controlled study shows the importance and rapidity of the tearing process under certain conditions.

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.

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