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The influence of edge undulation on vortex formation for low-aspect-ratio propulsors

  • Frieder Kaiser (a1) (a2), Jochen Kriegseis (a2) and David E. Rival (a1)

Abstract

Experiments to study the effect of edge undulation on vortex formation have been conducted on impulsively accelerated plates. Abstractions of propulsors found in nature are produced by imprinting undulatory features with varying wavelengths onto the circumferential vortex-forming edge of circular plates. The effects of the small-scale disturbances introduced by these modifications are accessed by means of force measurements and time-resolved particle image velocimetry. Investigations of four different geometries at two different Reynolds numbers reveal an insensitivity of the flow towards length scales smaller than or similar to the thickness of the feeding shear layer. However, the instabilities in the shear layer and the coherence of the vortex wake are influenced when the wavelength of the undulation exceeds the shear-layer thickness by a significant margin. This results in a force augmentation due to enhanced entrainment into the turbulent vortex core, and thus an associated faster vortex growth rate. Yet, contrary to prior expectations, the time of vortex pinch-off remains constant for all edge modifications. The cause–effect relationship behind the stability of the vortex wake is further investigated. While for small edge undulations a turbulent transition of the vortex core results in vortex pinch-off, for larger edge undulations the turbulent vortex core is found to be fed constantly with additional circulation from the shear layer.

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Copyright

This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited.

Corresponding author

Email addresses for correspondence: frieder.kaiser@kit.edu, d.e.rival@queensu.ca

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JFM classification

Type Description Title
VIDEO
Movies

Kaiser et al. supplementary movie 1
Early vortex-formation process (0≤ s/D≤2.3) for both Re and all plate geometries.

 Video (11.7 MB)
11.7 MB
VIDEO
Movies

Kaiser et al. supplementary movie 2
Differences in the long-term vortex-formation process (1.2≤s/D≤6.0) for the circular plate and plate 12 at Re=350k.

 Video (22.1 MB)
22.1 MB

The influence of edge undulation on vortex formation for low-aspect-ratio propulsors

  • Frieder Kaiser (a1) (a2), Jochen Kriegseis (a2) and David E. Rival (a1)

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