Concentration field characteristics of sediments entrained by rotor downwash flow

A helicopter flying near a sandy ground can easily induce the well-known brownout phenomenon, which is a big threat to both the rotor and engine of the helicopter. Although the brownout issue has been extensively studied, there is a great lack of data on the spatial concentration distribution characteristics of particles entrained by a rotor downwash flow. This paper presents a combined experimental and numerical investigation of the concentration field characteristics of particles entrained by a moderate-scale rotor hovering in ground effect. A rotor-sand test bench was set up for simulating an in-lab brownout cloud. The Discrete Phase Model (DPM) in ANSYS Fluent® was employed to track the trajectories of sediments entrained by the rotor downwash flow, which is validated by the current experimental data. The results suggest that both the number and mass concentrations are highly dependent on the spatial position including both the radial and altitude aspects, rotor height off the ground and rotor rotational speed, especially the mass concentration field. The results presented in this paper can not only provide a source of experimental data for future theoretical and numerical researches, but also offer some valuable design clues to turboshaft engine sand protection in engineering applications.