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Medientyp:
E-Artikel
Titel:
Prediction of Brownout Inception Beneath a Full-Scale Helicopter Downwash
Beteiligte:
Jasion, Gregory;
Shrimpton, John
Erschienen:
American Helicopter Society, 2012
Erschienen in:Journal of the American Helicopter Society
Sprache:
Englisch
DOI:
10.4050/jahs.57.042006
ISSN:
2161-6027
Entstehung:
Anmerkungen:
Beschreibung:
<jats:p>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.</jats:p>