72th Annual Meeting of the APS Division of Fluid Dynamics (November 23, 2019 — November 26, 2019)

P0018: Roll wave instability in Guinness

  • Tomoaki Watamura, Osaka University
  • Fumiya Iwatsubo, Osaka University
  • Kazuyasu Sugiyama, Osaka University
  • Kenichiro Yamamoto, Kirin HD Co. Ltd.
  • Yuko Yotsumoto, Kirin HD Co. Ltd.
  • Takashi Shiono, Kirin HD Co. Ltd.
DOI: https://doi.org/10.1103/APS.DFD.2019.GFM.P0018

After pouring Guinness beer in a pint glass, a vast number of small bubbles with a mean diameter of 50μm can be observed to descend (top). The rising motion of bubbles creates a clear-fluid (bubble-free) film above the inclined wall (right). The dense clear-fluid film falls, whereas the bubble-rich bulk rises, which is known as the Boycott effect [1]. We can also observe the fascinating texture motion as a number-density distribution of bubbles travelling downwards (bottom left).
To test the effect of inclination angle of the wall on the texture-formation, we poured Guinness beer in an inclined rectangular container, and observed how the texture forms (bottom right). We found the texture-formation is triggered by the inclination angle of the wall. We experimentally identify the critical condition for the texture-formation and conclude that the roll wave instability [2] is responsible for the texture-formation in a glass of Guinness beer [3].

[1] Boycott, A. E., Nature 104, 5 (1920).
[2] Needham, D. J. & Merkin, J. H., Proc. R. Soc. Lond. A 394, 259–378 (1984).  
[3] Watamura, T. et al., Sci. Rep. 9, 8718 (2019).

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