Physically-based Reduced Order Model for Unsteady Aerodynamic Loads of a L-shaped Gurney Flap

A physically-based linear reduced order model is developed for a NACA 0012 section oscillating in pitch and plunge, equipped with a L-tab Gurney flap in unsteady motion. The model allows for a quick and accurate computation of the first harmonic component of unsteady loads on a three degrees of freedom helicopter blade section model. Moreover, a physically-based identification procedure is carried out for fixed configurations of the airfoil and the L-tab, to complete the reduced order model with the mean steady contribution to aerodynamic loads. Numerical computations carried out with a finite volumes solver for compressible Reynolds Averaged Navier-Stokes equations, are performed and used as reference for the derivation of the reduced order model. Structured multi-block overlapped grids in relative motion are used as computational domain. The reliability of numerical simulations is verified by means of convergence analysis and comparisons with empirical and experimental data. The achieved reduced order model is an equivalent three segments piecewise mean line geometry, which correctly reproduces the effects of the airfoil mean line, including the L-tab, as well as contributions to loads of vortical structures behind the movable device. All these effects are well captured both on the mean value and the first harmonic of aerodynamic loads over the blade section. The strong connection of the parameters of the reduced order model with physical quantities is highlighted, as well as its predictive capability for arbitrary parameters of the imposed motion laws.