Long-wave instabilities of two interlaced helical vortices

We present a comparison between experimental observations and theoretical predictions concerning long-wave displacement instabilities of the helical vortices in the wake of a two-bladed rotor. Experiments are performed with a small-scale rotor in a water channel, using a set-up that allows the indiv...

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Bibliographic Details
Published in:Journal of physics. Conference series 2016-09, Vol.753 (3), p.32022
Main Authors: Quaranta, H U, Brynjell-Rahkola, M, Leweke, T, Henningson, D S
Format: Article
Language:English
Subjects:
Azimuthal wave number
Displacement instability
Filaments
Forecasting
Initial development
Instability modes
Linear stability theory
Longwave instability
Nonlinear evolutions
Physics
Rotors
Scale distortion
Torque
Vortex flow
Vortices
Wakes
Wind power
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Summary:We present a comparison between experimental observations and theoretical predictions concerning long-wave displacement instabilities of the helical vortices in the wake of a two-bladed rotor. Experiments are performed with a small-scale rotor in a water channel, using a set-up that allows the individual triggering of various instability modes at different azimuthal wave numbers, leading to local or global pairing of successive vortex loops. The initial development of the instability and the measured growth rates are in good agreement with the predictions from linear stability theory, based on an approach where the helical vortex system is represented by filaments. At later times, local pairing develops into large-scale distortions of the vortices, whereas for global pairing the non-linear evolution returns the system almost to its initial geometry.
ISSN:1742-6588
1742-6596
1742-6596
DOI:10.1088/1742-6596/753/3/032022