Computational analysis of a microtab-based aerodynamic load control system for rotor blades

A computational analysis of a microtab-based aerodynamic load control system for rotor blades is presented. The microtab load control concept consists of a small tab, roughly 1% of chord, that emerges approximately perpendicular from a lifting surface, typically near its trailing edge. Lift enhancement and mitigation is achieved by deploying the tab on the lower (pressure) and the upper (suction) surfaces, respectively. The computational methods applied in the development of this concept solve the governing Reynolds-averaged Navier-Stokes (RaNS) equations on structured grids. The effectiveness of the proposed load control system is studied for the GU 25-5(11)8 airfoil at subsonic conditions, and the SC1095 airfoil at transonic conditions. Tab deployment on the lower surface is shown to result in an upward shift in the lift curve in the linear regime, an increase in maximum lift coefficient, and an improvement in lift-to-drag ratio at moderate to high lift coefficients. The main effect of tab deployment on the upper surface is a downward shift in the lift curve in the linear regime at the expense of an increase in drag. These changes in the aerodynamic performance characteristics are strongly dependent on the chordwise location of the tab and its deployment height in relation to the boundary layer thickness.