AEROELASTIC INVESTIGATION OF HINGELESS HELICOPTER ROTOR IN HOVER Michael TODOROV 1 Ivan DOBREV 2 Fawaz MASSOUH 2 Cvetelina VELKOVA 1 michael.todorov@tu-sofia.bg ivan.dobrev@hotmail.com fawaz.massouh@ensam.eu tsveti@TF10109-1.tu-sofia.bg Department of Aeronautics, Technical University of Sofia, Sofia -1000, BULGARIA Laboratory of Fluids Mechanics, Arts et Metiers ParisTech, Paris-7513, FRANCE An aeroelastic modelling of pattern hingeless helicopter rotor in hover is presented in this paper. The coupled aeroelastic problem accounts for the mutual dependence between blade structure and rotor aerodynamics. The aerodynamic model uses Blade Element Momentum Theory (BEMT). BEMT gives good accuracy with respect to time cost. The structure model uses Finite Element Method (FEM). The investigation is based on the well-known solvers MATLAB and ANSYS. The obtained results show that the proposed modeling is efficient, rapid and gives reliable results. This modelling is also useful and applicable for airplane propellers, wind turbine rotors and airplane wings. Key Words: helicopter, aeroelasticity, aerodynamics, structural dynamics 1. Introduction Aerodynamic and inertia forces act on the helicopter blade in flight. These forces deform the helicopter blade and as a result, the aerodynamic forces distribution changes. The new aerodynamic forces distribution deforms the blade. In addition, that changes the aerodynamic forces distribution again. At a certain instant the aerodynamic and inertia forces, and elasticity forces will be balanced. Therefore the fully coupled aeroelastic problem must account for the mutual dependence between blade structure and aerodynamics. The last years of researches have provided significant successes in the prediction of airloads on the helicopter rotors. These predictions are based on a numerical approach, where the flow is simulated using Computational Fluid Dynamics (CFD) tools with moving boundary conditions. The computations normally include a comprehensive rotor code, coupled to Euler or Navier-Stockes solvers [Datta 2004, Servera 2002, Righi 2010]. The examples for a successful application of CFD are the codes FLUENT, TURNS of NASA, FLOWer of Deutshes Zentrum für Luft und Raumfahr, elsA and WAVES of ONERA [Servera 2002]. For aeroelastic calculations the CFD method has to be very time consuming. Thus it can be replaced by Blade Element Momentum Theory (BEMT) or the vortex wake method which show a good accuracy with respect to time cost [Leishman 2000]. In these methods, the helicopter blade is divided into a number of independent elements along the length of the blade. Each section of the blade acts as quasi 2-D airfoil, which produces aerodynamic forces and moments. The structure of helicopter blade has been modelled in different ways but mostly relies on a modified beam model or one-dimensional finite elements [Righi 2010]. The lumped-parameter approach is used to determine the helicopter blade deformations under the effects of aerodynamic and inertia forces. There the continuous blade is presented by a number of discrete segments, so that the partial differential equations of blade deformations are replaced by a set of simultaneous ordinary differential equations. The methods using this approach are the Holzer- Myklestad method [Bramwell 2001], collocation method [Bielawa 1992] and Finite Element Method (FEM) [Bielawa 1992, Floros 2000, Shen 2003]. The FEM solvers as ANSYS, ABAQUS, NASTRAN and ADAMS are often applied at the investigations of helicopter rotor dynamics. The advanced helicopter code called UMARC is well validated and extensively used in the helicopter rotor dynamics investigations. The rotor-fuselage equations are formulated using Hamilton’s principle and are discretized using finite elements in space and time. The blade airloads can be computed using quasi-steady aerodynamics, linear unsteady aerodynamics or nonlinear unsteady aerodynamics [Bir 1990, Freidmann]. Other successful helicopter code is CAMRAD. The used model is a combination of structural,