IDDES Investigation of Rotor Blade Tip Vortices in Hovering State with Tip Slots

The slots on a blade tip can effectively suppress the tip vortices by diffusing the core structure of a vortex and thus mitigate the adverse impacts of vortex interactions. In this paper, the effect of a slotted tip on vortex diffusion in the hovering state is investigated numerically by implementing the IDDES method using the fifth-order WENO scheme. The resulting wake flow field show that the number of secondary turbulent structures of so-called vortex worms near the slotted tip reduces significantly, indicating the weakening of vortex core rotation. It was found that the slotted tip reduced the peak value of velocity profiles in the vicinity of the vortex core by about 50%. The numerical result is close to the experimental conclusion. Correspondingly, the diameter of the vortex core is approximately doubled at each wake age relative to the baseline blade because the local flow passing through the slots will disintegrate the stable structure of the core region during the early stages of tip vortex generation. This promotes the turbulence mixture, resulting in the reduction in the vorticity value and rotating effect near the vortex core. Based on the overall results, the study of the slot parameters demonstrated that reducing the slot number or diameter will weaken the diffusing effect, causing a decrease in the flow rate.