Modelling visibility and surface deformation in particle-fluid flow fields generated by helicopter rotors

TL;DR

This paper models the particle cloud and surface deformation caused by helicopter rotors in sand, revealing how visibility and surface features depend on parameters, with some counterintuitive findings about altitude effects.

Contribution

It introduces a physically based mathematical model for wind-driven particle flows and surface deformation in helicopter brownout scenarios, highlighting parameter sensitivities.

Findings

Visibility can improve at lower altitudes under certain conditions.

Surface deformation features are sensitive to key parameters.

Counterintuitive visibility improvements are possible with specific parameter choices.

Abstract

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 consider a recently developed physically based rational mathematical model for the generation of wind-driven particle flow fields from otherwise static particle beds, one application of which is the scenario considered here. We introduce a directional opacity measure, defined for each observation angle from the helicopter cockpit, and show how visibility may vary in the model as certain parameters are varied. In particular, we demonstrate a counterintuitive result suggesting that, with specific yet potentially realistic parameter choices, pilot visibility may be improved in some viewing directions if the helicopter were hovering at a lower altitude. We also calculate the associated deformation of the upper surface of the particle bed, and show how certain surface deformation features may be sensitive to variation of key parameters.