Aerodynamic interference characteristics and wake evolution of rotor-wing in ground effect

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 grid technique, third-order MUSCL/CD scheme and RANS/LES (Reynolds-Averaged Navier-Stokes/Large Eddy Simulation) hybrid method. This study focuses on the variations in aerodynamic characteristics of the rotor-wing with different 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. The radial position of tip vortices exhibits an initial contraction followed by expansion, while the axial migration rate decreases. Furthermore, the helical motion of the blade tip vortices is characterized by phenomena including breakup, pairing and merging. Rotor thrust increases and wing downwash load decreases as ground height decreases. In comparison with the condition without ground effect, rotor thrust and figure of merit increase by up to 6.20% and 8.40% respectively, while wing downwash load drops by 59.05%. A computational method for Lagrangian Coherent Structures (LCS) was developed based on the fourthorder Runge-Kutta time integration method and the fourth-order central difference scheme to investigate the evolution of vortical structures in near-ground flow fields. By computing finite-time Lyapunov exponent fields at different instants, the spatiotemporal evolution of the vortex structures in the rotor-wing flow field under the ground effect 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 blade tip region due to downwash effects.