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Mutual inductance of two helical vortices

Published online by Cambridge University Press:  08 June 2015

András Nemes ,
David Lo Jacono ,
Hugh M. Blackburn  and
John Sheridan
András Nemes
Affiliation:
Fluids Laboratory for Aeronautical and Industrial Research (FLAIR), Department of Mechanical and Aerospace Engineering, Monash University, Clayton, VIC 3800, Australia
David Lo Jacono
Affiliation:
Fluids Laboratory for Aeronautical and Industrial Research (FLAIR), Department of Mechanical and Aerospace Engineering, Monash University, Clayton, VIC 3800, Australia Institut de Mécanique des Fluides de Toulouse (IMFT), CNRS, UPS, Université de Toulouse, Allée Camille Soula, 31400 Toulouse, France
Hugh M. Blackburn
Affiliation:
Department of Mechanical and Aerospace Engineering, Monash University, Clayton, VIC 3800, Australia
John Sheridan
Affiliation:
Fluids Laboratory for Aeronautical and Industrial Research (FLAIR), Department of Mechanical and Aerospace Engineering, Monash University, Clayton, VIC 3800, Australia
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Abstract

The pairing of helical tip vortices in the wake of a two-bladed rotor is investigated experimentally. Time-resolved particle image velocimetry measurements provide a clear temporal and spatial evolution of the vortical structures, highlighting the transition to instability and the effect of tip speed ratio and helical spacing. The temporal growth rate of the vortex system instabilities were measured and are shown to be dependent on helical spacing. The evolution of filaments and their growth rates support the argument that the mutual inductance mode is the driving mechanism behind the transition to an unstable wake. The measurements are in agreement with maximum growth rates predicted by linear stability analyses of single- and double-helix arrangements. In addition, the wake topology due to varying rotor load through tip speed ratio variation is shown to play an important role in the initial symmetry breaking that drives the wake transition.

JFM classification

Vortex Flows: Vortex instability Vortex Flows: Vortex interactions Wakes/Jets: Wakes
Type
Papers
Information
Journal of Fluid Mechanics , Volume 774 , 10 July 2015 , pp. 298 - 310
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Copyright
© 2015 Cambridge University Press 

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