Unsteady Criteria for Rotor Blade Airfoil Design

Abstract

The present paper deals with the definition and application of different unsteady criteria that may be considered in a dedicated aerodynamic design of rotorcraft airfoils. Today’s airfoil design methodologies for rotorcraft applications rely on steady computations and design criteria. Due to the inherent flow unsteadiness at forward flight, caused by variable incoming flow velocity, cyclic pitching as well as blade motion and deformation, it is however deemed necessary to further take into account unsteady aerodynamic effects and characteristics of the airfoil in the design process. Unsteady criteria are introduced for both 2D rotor-environment simulations with varying freestream Mach number and angle of attack and for high-frequency, small amplitude harmonic pitch oscillations at constant Mach number. By means of URANS simulations, with numerical settings validated against experiments, these criteria are exemplarily applied to the OA209 rotor blade airfoil geometry.