On the Possibilities of Brownout Mitigation Using a Slotted-Tip Rotor Blade

The development of brownout dust clouds generated by rotor blades with rectangular and slotted tips was predicted using a Lagrangian-Lagrangian model. The slotted-tip is comprised of four internal slots at the leading edge near the tip that are connected to the side edge, and are designed to inject small-scale vorticity and turbulence to rapidly diffuse the vortex core. The effects of the rectangular and slotted-tip blades on a rotor in ground effect operation was modeled by using a Lagrangian free-vortex method combined with a semi-empirical model for the vortex core growth in terms of the initial core radius and turbulent diffusion rate for each blade. The more diffused tip vortices trailed from the slotted-tip were found to create lower velocities and velocity excursions at the ground than was obtained with the rectangular blade, a result also verified experimentally. The Lagrangian dust cloud model predicted a significant reduction in dust uplift by means of all of the primary entrainment mechanisms that were modeled. The development of the dust cloud in the pilot’s field of view was also found to be slower, and the overall density of the brownout cloud in these regions was lower than with the rectangular blade. This outcome suggested better ground visibility for the pilot and, therefore, a more benign dust cloud was produced using the rotor with the slotted-tip blade. Overall, the results obtained thus far have shown that the slotted-tip blade has great potential for mitigating the severity of brownout conditions.