Coupled CFD And MBD Method For Aerodynamic Characteristics Analysis Of A Tilt Tri-rotor UAV

Tilt-rotor unmanned aerial vehicles(UAVs)has the characteristics of both vertical take-off and landing of rotorcrafts and high-speed and long-distance cruise of fixed-wing aircrafts,which has been studied by many scholars.As a kind of tilt-rotor aircraft,the tilt tri-rotor unmanned aerial vehicle has better overall performance than the tilt dual-rotor and tilt quad-rotor UAV.At present,aerodynamic features in conversion modes are simulated by computational fluid dynamics(CFD)solvers only,and the fuselage is fixed in the simulation process.This method does not take into account the fact that the motion of aircrafts bring effects on the aerodynamic forces and changes to the flow field.But in the simulation,especially in the simulation of conversion modes,moving aircrafts has a great impact on aerodynamic characteristics.This study developed a two-way coupled CFD/MBD computational method considering the whole model of a tilt tri-rotor UAV for helicopter and conversion modes and the complex dynamical simulation problem with large-space computational domain.Considering the motion of the tilt tri-rotor UAV in the flow field,the aerodynamic characteristics of the helicopter mode and conversion modes were analyzed.The multi-layer grid system is adopted to describe the relative motion among rotors and wing/fuselage in CFD solver.And different grid sizes,grid types and solution methods are used for different layer grid blocks.The Arbitrary Lagrangian-Eulerian(ALE)and dynamic grid are utilized for realizing the movement of the UAV in the grid.Moreover,in order to reduce the computational cost,the asynchronous solving strategy is presented.The revolving speed of the rear rotor is controlled to to keep the motion equilibrium of the UAV in simulations,while the left and right rotors tilt and the rotational speeds of them remain unchanged.As an example,the Georgia Tech(GT)rotor model was adopted as a validation case for the CFD solver.The developed two-way coupled computational method was then employed to simulate the helicopter mode and three conversion modes of the tilt tri-rotor UAV.The flow fields calculated by the coupling method were compared with that calculated by the CFD solver only.Simulation results show that the presented coupling method is effective and has the ability to capture essential aerodynamic characteristics.