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The presented work is dedicated to the numerical study of the aerodynamic characteristics of the helicopter rotor. Two approaches to modeling of the rotor are applied: the free wake model developed by the Authors with using steady airfoil characteristics and the Unsteady RANS method based on the Ansys Fluent software. The modes of hovering and horizontal flight in the range of advancing ratio μ = (0-0.45) are considered. The shapes of the rotor wake, the distributions of the normal force coefficient and the fields of inductive velocities for all considered flight modes are calculated. For a particular case with μ = 0.25 there is a comparison with experimental data. The time needed for calculation of the applied methods is estimated. Accuracy of the used methods in the framework of the solved task is analysed with taking into account used models assumptions. It is shown that in the range of μ = (0-0.25) the free wake model provides a fast and reliable calculation of the aerodynamic characteristics of the helicopter rotor. For values of μ > 0.35 it is necessary to take into account the unsteady characteristics of the airfoil.

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The research has been focused on aerodynamic characteristics of the Mi-8 helicopter main rotor in the hover and steep descent modes at rotor angles of attack αR = 90-30º, including vortex ring state area. The research is based on the original free wake model developed by the authors at Moscow Aviation Institute. Total and distributed aerodynamic characteristics, rotor wake shapes and streamlines have been calculated and analyzed. The vortex ring state area borders in the Vx-Vy (horizontal and vertical flight speed components) coordinates have been defined. Five criteria are used: growth of the required rotor blade pitch angle; growth of rotor power consumption with a fixed rotor thrust; increase of the averaged value of the induced velocities and amplitudes of the rotor thrust and torque pulsations. The calculation results have been compared with experimental and calculation data of other authors and indicate sufficient reliability and applicability of used free wake model for calculation and analysis of the vortex ring state modes of helicopter rotor. The results presented in the paper can also significantly supplement the available results of experimental and computational studies of the helicopter rotor operation at steep descent modes in the vortex ring state area.