Active Flow Control for Helicopters

Several active flow control helicopter applications aimed at improving aerodynamic performance have been studied at Onera and are presented in this paper. The distinction between applications for non-rotating or non-lifting parts and for rotating parts is presented. A first part deals with the application of steady/unsteady blowing to simplified rotor hub and fuselage shapes. The objective is to achieve significant drag reduction by suppressing the flow separation occurring in these areas. Numerical and experimental investigations are jointly performed to identify the best control strategies. The numerical efforts take into account the experimental constraints in the simulations. Significant work is done on the simplified fuselage drag reduction using various blowing actuations: synthetic jets, pulsed jets and steady blowing. The second part of the paper is dedicated to active flow control on rotor blades. A first application of deployable vortex generators for dynamic stall control is discussed. Then, more general active technologies aimed not only at improving the aerodynamic performance but also at reducing the vibratory loads or the noise radiation, are presented. Among the several active blade technologies that have been studied at Onera, both experimentally and numerically, this paper focuses on the active flap blade and the active twist blade concepts. The paper highlights the diversity of flow problems occurring on a rotorcraft and the various flow control strategies that must be considered to handle them. The numerical challenges to account for flow control in an unsteady environment are discussed for each flow control application.