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 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.

Ämnesord

NATURVETENSKAP  -- Fysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences (hsv//eng)

Nyckelord

Forecasting

Torque

Wakes

Wind power

Azimuthal wave number

Displacement instability

Initial development

Instability modes

Linear stability theory

Longwave instability

Nonlinear evolutions

Scale distortion

Vortex flow

Publikations- och innehållstyp

ref (ämneskategori)

art (ämneskategori)