scholarly journals Limit-cycle oscillations in unsteady flows dominated by intermittent leading-edge vortex shedding

2015 ◽  
Vol 55 ◽  
pp. 84-105 ◽  
Author(s):  
Kiran Ramesh ◽  
Joseba Murua ◽  
Ashok Gopalarathnam
Keyword(s):  
Limit Cycle ◽  
Vortex Shedding ◽  
Unsteady Flows ◽  
Leading Edge ◽  
Limit Cycle Oscillations ◽  
Leading Edge Vortex ◽  
Edge Vortex

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.

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

Observation and Discussion of Leading Edge Vortex Shedding From Laboratory-Scaled Cross-Flow Hydrokinetic Turbines in Counter-Rotating Configurations

2021 ◽  
Author(s):  
Minh Doan ◽  
Yuriko Kai ◽  
Takuya Kawata ◽  
Ivan Alayeto ◽  
Shinnosuke Obi
Keyword(s):  
Vortex Shedding ◽  
Power Output ◽  
Turbine Blades ◽  
Cross Flow ◽  
Leading Edge ◽  
Vertical Axis ◽  
Freestream Velocity ◽  
Leading Edge Vortex ◽  
Hydrokinetic Turbines ◽  
Edge Vortex

Abstract In 2011, John Dabiri proposed the use of counter-rotating vertical-axis wind turbines to achieve enhanced power output per unit area of a wind farm. Since then, various studies in the wind energy and marine hydrokinetic (MHK) literature have been dedicated to pairs of vertical axis turbines in both co-rotating and counter-rotating configurations, in terms of their power production, wake characterization, and optimal array design. Previous experimental works suggest an enhancement of up to 27.9% in the system power coefficient of pair configurations compared to a single turbine. Additionally, previous numerical studies have indicated that the increased power output is correlated with higher torque on the turbine blades which correspondingly produces a stronger leading edge vortex. This paper presents an extended investigation into a pair of laboratory scaled cross-flow hydrokinetic turbines in counter-rotating configurations. Experiments were conducted to observe, compare, and discuss the leading edge vortex shedding from the turbine blades during their positive torque phase. The turbines operated in a small water flume at the diameter-based Reynolds number of 22,000 with a 0.316 m/s freestream velocity and 4% turbulent intensity. Using a monoscopic particle image velocimetry setup, multiple realizations of the water flow around each blade at their positive torque phase were recorded and phase-averaged. Results show consistent leading vortex shedding at these turbine angles while a correlation between the turbine power performance and the vortex size and strength was observed.

scholarly journals Vortex-Sheet Representation of Leading-Edge Vortex Shedding from Finite Wings

2019 ◽  
Vol 56 (4) ◽  
pp. 1626-1640 ◽  
Author(s):  
Yoshikazu Hirato ◽  
Minao Shen ◽  
Ashok Gopalarathnam ◽  
Jack R. Edwards
Keyword(s):  
Vortex Shedding ◽  
Leading Edge ◽  
Vortex Sheet ◽  
Leading Edge Vortex ◽  
Edge Vortex

scholarly journals Leading-edge vortex shedding from rotating wings

2014 ◽  
Vol 46 (3) ◽  
pp. 031421 ◽  
Author(s):  
Dmitry Kolomenskiy ◽  
Yossef Elimelech ◽  
Kai Schneider
Keyword(s):  
Vortex Shedding ◽  
Leading Edge ◽  
Leading Edge Vortex ◽  
Edge Vortex

scholarly journals The leading-edge vortex and quasisteady vortex shedding on an accelerating plate

2010 ◽  
Vol 22 (3) ◽  
pp. 033601 ◽  
Author(s):  
Kevin K. Chen ◽  
Tim Colonius ◽  
Kunihiko Taira
Keyword(s):  
Vortex Shedding ◽  
Leading Edge ◽  
Leading Edge Vortex ◽  
Edge Vortex
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