Unsteady aerodynamics of miniature trailing-edge effectors based on indicial methods

The aerodynamics of miniature trailing-edge effectors (MiTEs), or active Gurney flaps, is explored in many aspects with regards to their applicability to rotorcraft. MiTEs hold strong potential to be used as active devices to improve performance, reduce vibrations, and reduce noise of rotors. Analysis of available computational fluid-dynamic (CFD) predictions for MiTEs positioned upstream from the trailing edge indicates the formation and convection of an unsteady vortex in the lower surface of the airfoil, immediately following a MiTE deployment. This disturbance can introduce non-harmonic components in the aerodynamic response, substantially affecting the loads and complicating the analysis. In order to account for these effects during routine helicopter performance and design studies, available CFD results are used to develop a reduced-order, less computationally-intensive model based on indicial concepts. The model extends a work previously done for trailing-edge MiTEs by incorporating a vortex model to predict the unsteady lift of upstream MiTEs. A physicsbased approach is adopted to minimize the number of constants and improve overall generality. The results from the unsteady-lift model are compared with CFD and experiments for different airfoils, MiTE deployment schedules, MiTE chordwise positions, and Mach numbers. Very good agreement is shown for a wide range of conditions that are typical of rotorcraft.