Abstract: To investigate the aerodynamic interference characteristics between rotor and wing of the tiltrotor aircraft in ground effect, a high-resolution flow field simulation framework was established based on the overset technique and hybrid RANS/LES(Reynolds-Averaged Navier-Stokes/Large Eddy Simulation) method. This study focuses on investigate the variations in aerodynamic characteristics of the rotor-wing in varying heights above the ground. Results demonstrate that the presence of the ground and wing inhibits the development of rotor downwash, significantly altering the wake evolution process. Compared to out of ground effect condition, the radial position of tip vortices exhibits an initial contraction followed by expansion, while the axial migration rate decreases. With rotor thrust increasing and wing download decreasing as ground height decreases, compared to the out of ground effect condition, rotor thrust and figure of merit increase by up to 6.20% and 8.40% respectively, while wing download drops by as much as 59.05%. A computational method for Lagrangian coherent structures was developed using a fourth-order Runge-Kutta time integration and fourth-order central difference scheme to investigate the evolution of vortical structures in ground flow fields. By computing finite-time Lyapunov exponent fields at different instants, the spatiotemporal evolution of the vortex structures within the rotor-wing in the ground flow field was clarified. This revealed the physical mechanism by which recirculating structures maintain stability through continuous transport of fluid parcels, as well as the flow mechanism leading to reduced aerodynamic forces in the tip region due to downwash effects.

Key words: tiltrotor aircraft, ground effect, RANS/LES hybrid method, Lgrangian coherent structures, wake