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Propulsion generated by diffusion-driven flow

Nature Physics volume 6, pages 516–519 (2010)Cite this article

Abstract

Buoyancy-driven flow, which is flow driven by spatial variations in fluid density1, lies at the heart of a variety of physical processes, including mineral transport in rocks2, the melting of icebergs3 and the migration of tectonic plates4. Here we show that buoyancy-driven flows can also generate propulsion. Specifically, we find that when a neutrally buoyant wedge-shaped object floats in a density-stratified fluid, the diffusion-driven flow at its sloping boundaries generated by molecular diffusion produces a macroscopic sideways thrust. Computer simulations reveal that thrust results from diffusion-driven flow creating a region of low pressure at the front, relative to the rear of an object. This discovery has implications for transport processes in regions of varying fluid density, such as marine snow aggregation at ocean pycnoclines5, and wherever there is a temperature difference between immersed objects and the surrounding fluid, such as particles in volcanic clouds6.

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Figure 1: Spontaneous propulsion of a triangular wedge in a density-stratified fluid.
Figure 2: PIV visualizations of the flow field around a moving wedge.
Figure 3: Experimental results for u as a function of the governing parameters.
Figure 4: Numerical simulation of diffusion-driven flow induced by a fixed wedge.

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Acknowledgements

We thank R. Stocker, E. Lauga and C. C. Mei for discussions; W. Etheridge, P. Steinmetz and C. Lenahan for experimental assistance; A. Gallant for fabrication of experimental apparatus; O. Fringer for access to computational resources; and G. Buck, J. W. M. Bush, E. Johnson, W. R. Young, C. Wunsch and J. H. Peacock for reading the manuscript. This work was supported by the NSF CBET programme. M.F.B. acknowledges the support of the National Science Foundation MSPRF programme. This research used resources of the National Energy Research Scientific Computing Center, which is supported by the Office of Science of the US Department of Energy under Contract No. DE-AC02-05CH11231.

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Authors and Affiliations

  1. Department of Mechanical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, USA

    Michael R. Allshouse & Thomas Peacock

  2. Environmental Fluid Mechanics Laboratory, Stanford University, Yang & Yamasaki Environment & Energy Building, 473 Via Ortega, Office M15, Stanford, California 94305, USA

    Michael F. Barad

Authors
  1. Michael R. Allshouse
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  2. Michael F. Barad
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  3. Thomas Peacock
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Contributions

T.P. conceived the original idea, supervised the research and wrote the manuscript. M.R.A. carried out the experiments, ran some numerical simulations and analysed the numerical data. M.F.B. ran the stratified flow simulations.

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Correspondence to Thomas Peacock.

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The authors declare no competing financial interests.

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Allshouse, M., Barad, M. & Peacock, T. Propulsion generated by diffusion-driven flow. Nature Phys 6, 516–519 (2010). https://doi.org/10.1038/nphys1686

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