Nonlinear Aeroelastic Response Simulation of Rotor Blades with Trailing Edge Flap Controls

Abstract

*† ‡ In the study, a numerical simulation tool to capture major vehicle flight and blade dynamic characteristics has been developed. A generic compound helicopter configuration which utilizes broader range of rotor rpm changes, auxiliary lift, and tail propulsion as additional flight control inputs is considered. Rotor of the helicopter is controlled by trailing edge flaps. The major flight characteristics and nonlinear rotor blade aeroelastic response are obtained starting from constant rotor speed forward flight to rotor rpm change quasisteady forward flight phases. For trim conditions, nonlinear aeroelastic partial differential equations (PDE’s) are solved numerically by a conditionally stable explicit finite difference scheme developed by previous studies. The major introduced result of this study is the development of a numerical simulation tool which enables designers to capture vehicle flight characteristics and blade dynamic responses. The simulation tool is primarily used to generate blade and hub components stresses, flow field perturbations due to maneuver and blade deflections and blade dynamic stall conditions. These simulations are aimed to be the replacement of outputs of different sensors on vehicle and rotor systems as well as physical effects of aeroelastic interactions around the blade in a real compound helicopter. Simulated sensor outputs are utilized as parameters in objective functions and as physical constraints on the flight control problem. As the first step of study, trim equations with vector notation for conventional control inputs are used. Additional to these conventional control inputs, left and right canard and horizontal tail incidences as well as longitudinal and lateral components of the tail propulsion are also considered as additional control inputs. Rotor rpm variations are allowed in a broad bandwidth to expand the design space for the optimization procedure. Main rotor as well as total power/torque required of the compound vehicle is governed to maintain the flight. Numerical solutions are obtained for vehicle trim and rotor blade aeroelastic nonlinear PDE’s simultaneously. Nonlinear aeroelastic rotor blade PDE’s are solved to obtain time dependent motion of the elastic axis where blade is modeled as long slender beam deflecting with geometric nonlinearities. Three dimensional deformation of the blade, stresses at blades and another load bearing parts, flow field fluctuations both due to blade deflections and vehicle motion and dynamic stalling effects are obtained. The tool is used to generate simulations of blade and hub stresses, flow field around blade and blade stalling conditions which can be used to generate the necessary design parameters closely related with the rotor slowing flight and blade dynamic characteristics needed for analysis and design. With this approach “Response Surfaces” generated for parametric design and optimization can reflect these important dynamic effects in the early stages of the Concept Exploration and Design studies.