No abstract

In this study, a computational fluid dynamics approach based on solving the Reynolds-averaged Navier-Stokes equation and shear stress transport (SST) (Menter) k-ω turbulence model is used to solve the rotor in ground effect. A discrete element method based on solving the Hertz-Mindlin (noslip) contact model and considering the real physical properties and collision is used to solve the motion and distribution of sediment particles in the field. By coupling the two approaches, the dust cloud development in the ground-effect flow field of a helicopter with rectangular-tip and slotted-tip blades is simulated for six seconds. The characteristics of the flow field are analyzed, and the influence of the flow field generated by the two types of blades on the movement and distribution of sediment particles on the ground and the subsequent dust cloud development over time are compared. The relatively long time of numerical results show that the sediment particles initially located on the ground are uplifted by the interaction between the blade tip vortex and the ground. Over time, the particles become more concentrated around the tip vortex core. The sediment particles in the dust cloud move primarily in the radial and axial directions of the rotation center, and the circumferential movement is not significant. The optimized slotted-tip blade provides better dissipation of the tip vortex core intensity near the ground than the rectangular-tip blade, thus weakening the entrainment effect of the sediment particles on the ground and reducing the dust cloud concentration around the disc plane.

Coupled ship/coaxial-rotor simulations have been conducted to investigate the rotor loads of a shipborne coaxial-rotor helicopter during a vertical landing based on Reynolds-averaged Navier-Stokes (RANS) solver. In order to achieve two-way coupling and overcome the limitations of the momentum source method in solving the unsteady aerodynamic problems, the moving overset mesh method is employed to simulate the complex highly unsteady aerodynamic interactions between the lower/upper rotor, flight deck and hangar-door through the vertical descent. To identify pilot workload and control strategy during this phase, the results in terms of time-averaged and rootmean-square (RMS) rotor loads are discussed. The time-averaged loads show that the coaxial-rotor helicopter suffers an increase in thrust and a sharp decrease in torque difference between lower and upper rotors during the vertical landing. It suggests that the pilot has to reduce not only the collective control input, but also the differential collective pitch, to stabilize the heading of the coaxial rotors helicopter. The RMS results indicate that the aerodynamic loads of the lower and upper rotors could couple with each other, and may eventually magnify the overall unsteady loading levels of the coaxial rotor. In addition to the ground effect, the recirculation flow regime will get stronger and lead to a sharp increase in RMS roll as the rotor moves along the vertical descent path. Furthermore, the influences of hangar-door state and the location of landing spot are investigated. The findings imply that opening the hangar-door can significantly reduce the pilot workload, and descending a helicopter to a landing spot which is more closed to the hangar can decrease the RMS load levels, especially during the latter stage of vertical descent. However, the helicopter tends to be pulled towards hangar-door more easily due to greater reduction in pitch moment.