# Aperiodicity in the near field of full-scale rotor blade tip vortices

Aperiodicity in the near field of full-scale rotor blade tip vortices Blade tip vortices are the dominant vortical structures of the helicopter flow field. The inherent complexity of the vortex dynamics has led to an increasing interest in full-scale in situ experiments, where the near field, closely behind the blade, is of particular interest, since measures of vortex control mostly target this initial stage of development. To examine the near field, three-component particle image velocimetry (PIV) measurements of blade tip vortices of a full-scale helicopter in simulated hover flight in ground effect were conducted. A feasible and robust evaluation procedure was developed to minimise the shortcomings of full-scale PIV applications, such as a moderate spatial resolution and an elevated measurement noise level. At vortex ages ranging from $$\psi_{\rm v}=1^{\circ}$$ to 30°, a pronounced aperiodicity and asymmetry of the vortex were observed in -sections perpendicular to the vortex axes. At $$\psi_{\rm v}=1^{\circ}$$ , a preferential orientation of the vortex was observed. For increasing wake age, vortex wandering increased while the asymmetry of the vortex cores decreased. The high level of aperiodicity and core asymmetry must be taken into account when considering phase-averaged vortex characteristics in the near wake region. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Experiments in Fluids Springer Journals

# Aperiodicity in the near field of full-scale rotor blade tip vortices

, Volume 50 (6) – Dec 12, 2010
10 pages

Publisher
Springer-Verlag
Subject
Engineering; Engineering Thermodynamics, Heat and Mass Transfer; Fluid- and Aerodynamics; Engineering Fluid Dynamics
ISSN
0723-4864
eISSN
1432-1114
D.O.I.
10.1007/s00348-010-1016-8
Publisher site
See Article on Publisher Site

### Abstract

Blade tip vortices are the dominant vortical structures of the helicopter flow field. The inherent complexity of the vortex dynamics has led to an increasing interest in full-scale in situ experiments, where the near field, closely behind the blade, is of particular interest, since measures of vortex control mostly target this initial stage of development. To examine the near field, three-component particle image velocimetry (PIV) measurements of blade tip vortices of a full-scale helicopter in simulated hover flight in ground effect were conducted. A feasible and robust evaluation procedure was developed to minimise the shortcomings of full-scale PIV applications, such as a moderate spatial resolution and an elevated measurement noise level. At vortex ages ranging from $$\psi_{\rm v}=1^{\circ}$$ to 30°, a pronounced aperiodicity and asymmetry of the vortex were observed in -sections perpendicular to the vortex axes. At $$\psi_{\rm v}=1^{\circ}$$ , a preferential orientation of the vortex was observed. For increasing wake age, vortex wandering increased while the asymmetry of the vortex cores decreased. The high level of aperiodicity and core asymmetry must be taken into account when considering phase-averaged vortex characteristics in the near wake region.

### Journal

Experiments in FluidsSpringer Journals

Published: Dec 12, 2010

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