Novel approach to helicopter brownout based on vortex and discrete element methods

So far, numerical methods used for brownout considered empirical and semi-empirical models, but particle-particle and particle-surface interactions were not extensively researched. In this work, a novel approach to helicopter brownout coupling a vortex method and a discrete element method is developed. In this approach, the dynamics of individual sand particles, the particle-particle and particle-surface interactions are directly computed and coupled with the flow field of a helicopter in ground effect through aerodynamic forces. The method is demonstrated for a scaled rotor of 172 mm diameter in ground effect, as well as for the US Army EH-60L in brownout. The results show that the predicted radial velocity profiles and wall jet compare well with experiments and published CFD results, and the predicted behavior of brownout agrees with observations from flight tests of the EH-60L. Compared with Lagrangian dust cloud simulation, the predicted relative error of dust cloud is reduced by 57.09% in the taxi-pass case and 28.76% in the approach-to-touchdown case.