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.
The paper is focused on numerical modeling of the aerodynamic characteristics of a full-scale coaxial main rotor in hover. The simulation was performed using two approaches of computational fluid dynamics (CFD): the original free wake model (FWM) developed by the authors and the unsteady Reynolds-averaged Navier-Stokes (URANS) equations method based on the Ansys Fluent software. The structure of the rotor vortex wake, flow images, vorticity and induced velocity fields, total and distributed aerodynamic characteristics of the rotor, including the rotor performance and figure of merit diagrams, have been analyzed. A comparison between FWM/URANS based calculations and calculated/experimental data by other authors has been performed. A satisfactory match of these data confirms reliability of used methods when modeling the aerodynamic characteristics of coaxial rotors. The FMW demonstrates a significant advantage in speed and resources intensity when calculating the total aerodynamic characteristics of a coaxial rotor. The URANS method makes it possible to model with significant accuracy the effects associated with the blade vortex interactions and pressure distribution over the blade surface. Finally, conclusions about most effectiveness of joint application of considered methods in solving complex problems of coaxial rotor aerodynamics has been made.
The paper is focused on the numerical study of the aerodynamic characteristics of 3bladed and scissors tail rotors used on Mi-8/17 series helicopters. The hovering and axial flow modes, including the Vortex Ring State (VRS) area are considered. The free wake model developed by authors is used in the research. The study has been performed for two approaches: with a fixed blade pitch angle and with a fixed time-average thrust value. The dependences of the rotor thrust and torque coefficients vs. axial flow velocity and vs. number of revolutions of a rotor have been obtained. The vortex wake shapes and flow images via streamlines have been analyzed. The comparative analysis of the results has been performed. Scissors rotor demonstrates better aerodynamic characteristics in comparison with 3-bladed rotor. Among them: increased hovering efficiency, lower level of thrust and torque pulsations in the VRS modes, smaller power consumption while constant thrust. The authors came to the conclusion about the greater efficiency of the aerodynamic design of scissors tail rotor compared to 3-bladed rotor both in hover and in the VRS modes area.
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