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Prediction of brownout inception beneath a full-scale helicopter downwash

Prediction of brownout inception beneath a full-scale helicopter downwash
Prediction of brownout inception beneath a full-scale helicopter downwash
Dust entrained by low flying helicopters leads to the degraded visual environment, brownout. Particle inception is a critical stage in the development of the dust cloud. Here, near-wall Lagrangian particle forces are considered through analyzing an approximate time-averaged full-scale rotor flow. This simplified flow does not attempt to predict brownout, instead it provides scales and velocity data in the near-wall region, compares the role of particle-fluid forces, and provides a foundation for Lagrangian entrainment models. The analysis shows that three characteristic particle sizes are exposed to different physics in different boundary layer zones, a function of the distance from the helicopter. Drag is the dominant aerodynamic force, cohesion is large for small particles, but wall-bounded lift is sufficient to entrain medium-sized particles. A complementary analytical prediction of tip vortices found that both large-scale inviscid features and small-scale viscous features of the boundary layer are significant.
0002-8711
1-13
Shrimpton, J.S.
9cf82d2e-2f00-4ddf-bd19-9aff443784af
Jasion, G.
16cfff1d-d178-41d1-a092-56e6239726b8
Shrimpton, J.S.
9cf82d2e-2f00-4ddf-bd19-9aff443784af
Jasion, G.
16cfff1d-d178-41d1-a092-56e6239726b8

Shrimpton, J.S. and Jasion, G. (2012) Prediction of brownout inception beneath a full-scale helicopter downwash. Journal of the American Helicopter Society, 57 (4), 1-13. (doi:10.4050/JAHS.57.042006).

Record type: Article

Abstract

Dust entrained by low flying helicopters leads to the degraded visual environment, brownout. Particle inception is a critical stage in the development of the dust cloud. Here, near-wall Lagrangian particle forces are considered through analyzing an approximate time-averaged full-scale rotor flow. This simplified flow does not attempt to predict brownout, instead it provides scales and velocity data in the near-wall region, compares the role of particle-fluid forces, and provides a foundation for Lagrangian entrainment models. The analysis shows that three characteristic particle sizes are exposed to different physics in different boundary layer zones, a function of the distance from the helicopter. Drag is the dominant aerodynamic force, cohesion is large for small particles, but wall-bounded lift is sufficient to entrain medium-sized particles. A complementary analytical prediction of tip vortices found that both large-scale inviscid features and small-scale viscous features of the boundary layer are significant.

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More information

Published date: October 2012
Organisations: Optoelectronics Research Centre, Faculty of Engineering and the Environment

Identifiers

Local EPrints ID: 349235
URI: http://eprints.soton.ac.uk/id/eprint/349235
ISSN: 0002-8711
PURE UUID: a5f20409-270f-4704-aa53-e77ac0ec45e4
ORCID for G. Jasion: ORCID iD orcid.org/0000-0001-5030-6479

Catalogue record

Date deposited: 26 Feb 2013 16:25
Last modified: 26 Nov 2019 01:43

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