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lhlke ONERA, Clzritillorz. Frrrrrce DLR, B,orrr~sd~s,eig. Go,rrotl)'n v o numerical methods (the DLR code FLOWer and the ONERA code CANARI), based on the resolution of the Reynolds Averaged Navier-Stokes equations, are applied in this paper in order to compute the performance of helicopter rotors in hover. The comparison of computed performance with experimental results of the scale-1 BO-105 rotor and the model 7A rotor assuming rigid blades shows a significant overestimation of rotor thrust and power. An easy and efficient way to account for the blade elasticity in torsion is then described. The new aeroelastic computations show much better agreement with experiment, especially for the hingeless BO-105 rotor, even if the figures of merit are underestimated for a given thrust coefficient. It is finally shown that accounting for a laminar-turbulent boundary layer (instead of a fully turbulent boundary layer) in the Navier-Stokes code significantly increases the estimated figure of merit, thus improving the correlation between computations and experiment. NotationAz

This paper is part of a DLR research programme to develop a three-dimensional Euler code for the calculation of unsteady flow fields around helicopter rotors in forward flight. The present research provides a code for the solution of Euler equations around aerofoils in arbitrary unsteady motion. The aerofoil is considered rigid in motion, and an O-grid system fixed to the moving aerofoil is generated once for all flow cases. Jameson's finite volume method using Runge-Kutta time stepping schemes to solve Euler equations for steady flow is extended to unsteady flow. The essential steps of this paper are the determination of inviscid governing equations in integral form for the control volume varying with time in general, and its application to the case in which the control volume is rigid with motion. The implementation of an implicit residual averaging with variable coefficients allows the CFL number to be increased to about 60. The general description of the code, which includes the discussions of grid system, grid fineness, farfield distance, artificial dissipation, and CFL number, is given. Code validation is investigated by comparing results with those of other numerical methods, as well as with experimental results of an Onera two-bladed rotor in non-lifting flight. Some numerical examples other than periodic motion, such as angle-of-attack variation, Mach number variation, and development of pitching oscillation from steady state, are given in this paper.

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