Long-wave instabilities of two interlaced helical vortices

The Science of Making Torque from Wind

Quaranta, H.U.^1,2 ; Brynjell-Rahkola, M.^3 ; Leweke, T.^1 ; Henningson, D.S.^3

IRPHE, Aix Marseille Univ, CNRS, Centrale Marseille, Marseille

13384, France^1

Aerodynamics Department, AIRBUS HELICOPTERS, Marignane

13725, France^2

Linné FLOW Centre, KTH Mechanics, Royal Institute of Technology, Stockholm

SE-10044, Sweden^3

关键词: Azimuthal wave number;    Displacement instability;    Initial development;    Instability modes;    Linear stability theory;    Longwave instability;    Nonlinear evolutions;    Scale distortion;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/753/3/032022/pdf
DOI  :  10.1088/1742-6596/753/3/032022

来源: IOP

【 摘 要 】

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.