Toward a physics based entrainment model for simulation of helicopter brownout

Abstract

Brownout is the name given to the degraded visual environment that can develop around a helicopter as it operates in dusty conditions. The dust cloud produced reduces visibility and makes landing the helicopter extremely difficult, there is potential for damage to the aircraft or even loss of life. This thesis works towards understanding the physical processes occurring in the generation of the dust cloud and the application of this understanding in a computational model for dust entrainment. Current brownout simulations use empirical entrainment models originally developed for aeolian sand movement. These models use parameters fitted to experimental evidence, whilst they may recreate the dust conditions of certain scenarios there is need for a physical model that can produce accurate results for prospective aircraft or scenarios. The physical brownout system is a multiphase system made up of particle dynamics of the scales less than a millimetre and fluid scales as large as metres. In this thesis computational modelling of particle systems, fluid systems and multiphase flow systems are used to understand how the rotor wake entrains particles. A model scale 3D unsteady rotor simulation was performed both in and out of ground effect. The flow compares well with experimental results. The ground vortex interaction is quantified. The model scale analysis is complemented by a full scale but steady, 2D, axisymmetric rotor flow analysis. The steady flow is demonstrated to provide sufficient aerodynamic force to lift typically medium sized particles from the ground. The Discrete Element Method is a Lagrangian particle simulation method, in this thesis it is investigated numerically and then the physical behaviour is assessed in a simulation of a probe indentation experiment. The dynamic behaviour matched the experiment well. The Discrete Element Method is recommended as a particle modelling method for a brownout modelling solution. Modelling brownout is extremely difficult due to the range of scales involved. This thesis provides an in depth understanding of the helicopter flow field at small and large scales and the aerodynamic forces and entrainment mechanisms of particles on the ground in the wake of a helicopter.

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ORCID for G. Jasion: orcid.org/0000-0001-5030-6479

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