Research On Aerodynamic Characteristics Of Coaxial Twin Rotors In Ground Effect

Ground effect have a significant impact on the helicopter performance when vertical take-off and landing or flight near ground, at present, the study in ground effect basic stay in single rotor with tail rotor configurations, based on the advantage of coaxial twin rotors helicopter, it will have great applications in the future, so in this paper, the aerodynamic characteristics of coaxial rotors in ground effect will be studied.Based on time marching algorithm established a rotor free wake model which suitable for analysis the aerodynamic characteristics of coaxial twin rotors, and the surface element method are adopted to simulate the influence of the flow field near around. In the process of modeling, the blade flapping response is derived under assumption of rigid blade, the blade aerodynamic model using Weissinger-L first-order lifting surface model which considering the three-dimensional effect of blade, and fully considering the aerodynamic interference between rotor and rotor or rotor and ground, balancing coaxial rotors system under steady state, start numerical iteration solution after coupling those models.In this paper, the development of the coaxial twin rotors aerodynamic characteristics analysis model is based on the single rotor free wake model, it can use to analysis single rotor and coaxial rotors flow field characteristics in ground effect, through the existing experimental dates and the dates form experimental study in this paper, the reliability of the mathematical model was verified.At last, using the calculation model which verification by experience dates, Calculation and analysis the rotor wake geometry and the flow field induced inflow characteristics of single rotor in hovering and forward flight state in ground effect. especially emphasizes the aerodynamic interference characteristics between the rotor and ground, To calculate the horizontal ground and there is a certain angle of tilt ground rotor’s free wake geometry, and studied the aerodynamic interference characteristics of coaxial rotors, The existence of the ground has certain disturbance to the flow field around the rotors, ground meets through the boundary conditions, the impact of ground leading free-wake radial expansion and roll up. Ground has especially influence to the force of lower rotor. Through the calculation and analysis of coaxial rotors aerodynamic interference characteristics, some meaningful conclusions are obtained.