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Abstract
Two-dimensional flows over harmonically oscillating symmetrical aerofoil at reduced frequency of 0.1 were investigated for a Reynolds number of 135,000, with focus on the unsteady aerodynamic forces, pressure and vortex dynamics at post-stall angles of attack. Numerical simulations using ANSYS® FLUENT CFD solver, validated by wind tunnel experiment, were performed to study the method of sliding mesh employed to control the wing oscillation. The transport of flow was solved using incompressible, unsteady Reynolds-Averaged Navier-Stokes equations. The 2-equation k-e realizable turbulence model was used as turbulence closure. At large angle of attack, complex flows structure developed on the upper surface of the aerofoil induced vortex shedding from the activity of separated flows and interaction of the leading edge vortex with the trailing edge one. This interaction at some stage promotes the generation of lift force and delays the static stall. In this investigation, it was found that the sliding mesh method combined with the k-e realizable turbulence model provides better aerodynamic loads predictions compared to the methods reported in literature.
Highlights
Among the earliest documented phenomena of dynamic stall, there is the report of Kramer (1932) summarizing his experimental investigation on the effect of vertical gust on a wing stress
The results presented in this paper refer to the aerofoil subjected to a harmonic oscillation which is defined as a function of the angle of attack variation, α(t) = αm + αo sin(ωt), where ω is the oscillation frequency
The purposes of this research were to investigate the potential of sliding mesh and k-ε realizable turbulent model in the simulation of aerofoil in unsteady oscillation, in order to support wind tunnel experiment, to fully understand the aerodynamic behavior of aerofoils in harmonic oscillation and for the design of control system for flexible wing
Summary
Among the earliest documented phenomena of dynamic stall, there is the report of Kramer (1932) summarizing his experimental investigation on the effect of vertical gust on a wing stress. Numerous experimental papers (McCroskey 1981; Kim and Chang 2009; Lee and Gerontakos 2004; McCroskey et al 1976; Panda and Zaman 1994; Coton and Galbraith 1999) and numerical investigations (McCroskey and Pucci 1982; Ericsson and Reding 1970; Gaitonde and Fiddes 1993; Dumlupinar and Murthy 2011; Barakos and Drikakis 1999) have been carried out and show that the unsteady flow can be separating or reattaching over a large portion of the upper surface of an aerofoil, features which reverse flow circulation, formation and shedding of leading and trailing vortex system that induces non-linear fluctuating pressure field and produce transient variation in forces and moments that are different to its steady-state conditions (Lee and Gerontakos 2004). The solution of the CFD using sliding mesh is compared against dynamic mesh method and available experimental data
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