Linear Reduced-Order Model for Unsteady Aerodynamics of an L-Shaped Gurney Flap

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Linear Reduced-Order Model for Unsteady Aerodynamics of an L-Shaped Gurney Flap

Motta, Valentina / Quaranta, Giuseppe

The purpose of the work is to investigate the mechanism that underlies the development of unsteady loads by a novel L-shaped Gurney flap conceived to perform vibration control on rotorcraft blades. The device is combination of a spoiler with a Gurney flap. Exploiting the capabilities of a Reynolds-averaged Navier–Stokes flow solver employing the overset mesh approach, several numerical simulations are carried out at low Mach number. These simulations are used to develop a physically based linear reduced-order model in the frequency domain for the unsteady lift and pitching moment of a NACA 0012 airfoil, considering as input the pitch and plunge harmonic oscillations of the airfoil, together with the oscillations of the L-shaped Gurney flap. The aerodynamic assessment of the L-tab shows that the behavior of the loads can be predicted using an equivalent flat-plate model to represent the airfoil composed by three segments: the first representing the fixed part of the airfoil, the second representing the longitudinal edge of the tab, and the third representing the counter-rotating vortical structures that appear behind the movable device. The same approach is used to model the static lift and moment enhancements, as due to an equivalent camber modification effect. The strong connection of the parameters of the reduced-order model with the physical quantities is highlighted as well as its predictive capability for arbitrary parameters of the imposed motion laws.