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

Ramesh, K. , Gopalarathnam, A., Granlund, K., Ol, M. V. and Edwards, J. R. (2014) Discrete-vortex method with novel shedding criterion for unsteady airfoil flows with intermittent leading-edge vortex shedding. Journal of Fluid Mechanics, 751, pp. 500-538. (doi:10.1017/jfm.2014.297)

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Publisher's URL: http://dx.doi.org/10.1017/jfm.2014.297

Abstract

Unsteady 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 A0 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.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Ramesh, Dr Kiran
Authors: Ramesh, K., Gopalarathnam, A., Granlund, K., Ol, M. V., and Edwards, J. R.
College/School:College of Science and Engineering > School of Engineering > Aerospace Sciences
Journal Name:Journal of Fluid Mechanics
Publisher:Cambridge University Press
ISSN:0022-1120
ISSN (Online):1469-7645

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
UNSPECIFIED9550Theoretical, Computational, and Experimental Studies of the Aerodynamics of Perching FlightDr. Ashok GopalarathnamAFOSRUNSPECIFIEDUNSPECIFIED