| Rotorcraft brownout is in-flight visibility restriction caused by clouds of sand and dust particles during landing, take off, and near ground flight operations in arid desert terrain. This complex phenomenon is caused by entrainment of dust, sand, and ground particles by rotor downwash and is compounded by fuselage geometry and its orientation with respect to the ground. Nonlinear forces and moments on the fuselage, and highly unsteady wind velocities are common in near ground operations and play a significant role in the behavior of the particulate clouds that create the brownout condition.;In this current research, an efficient Computational Fluid Dynamics (CFD) based tool has been developed to analyze and predict the dust cloud formation and kinematics in the vicinity of a single or multiple rotor complete aircraft configurations operating near the ground. The flow field is calculated by solving Reynolds averaged Navier-Stokes equation by finite volume approach using the SIMPLER algorithm. The solver integrates the rotor downwash and the ground interference in a coupled viscous solution procedure wherein the rotor blades are modeled as steady momentum sources. The transport of dust is solved using an Eulerian-based dust transport equation. The modeling of dust lift-off criteria and entrainment is accomplished through empirical formulation used in geophysical research. The computational tool is used to study the effect of fuselage geometry on the rotor wake, ground signature, and brownout. The effect of different rotor configuration and variation of rotor height on rotor wake, ground signature and brownout is also discussed. |
