Modelling helicopter brownout

What is it about?

As a helicopter descends towards a bed of sand, a high velocity particle laden cloud can form around the helicopter body, a phenomenon known as “brownout”, and a consequence of which can potentially be a significant deterioration in visibility for the helicopter pilot. Here, we describe a mathematical model that can be used to simulate this phenomenon, and show how it can be used to enable a greater understanding of how pilot visibility and surface deformation may be affected by parameters representing, for example, the height of the helicopter, the ratio of swirl velocity to downdraft velocity, and the properties of the sand bed.

Featured Image

Photo by paul jespers on Unsplash

Photo by paul jespers on Unsplash

Why is it important?

Simulating helicopter brownout is notoriously challenging. In recent work (https://doi.org/10.1017/jfm.2024.740), we developed a better understanding of how sand is lifted into the air by the downdraft and swirling flow generated by a hovering helicopter. Here, we demonstrate how key features of the simulation, such as pilot visibility and surface deformation, can be easily calculated from the resulting mathematical model. We hope this will lead to a better understanding of these phenomenon, and ultimately improved rotorcraft safety.