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Research > Stratified Flows

Buoyancy-driven flow, which is flow driven by spatial variations in fluid density, lies at the heart of a variety of physical processes, including mineral transport in rocks, the melting of icebergs and the migration of tectonic plates. Here, we report on a new discovery that buoyancy-driven flows can also generate propulsion. Specifically, we find that when an asymmetric object floats in a density-stratified fluid, the diffusion-driven flow at its sloping boundaries draws energy and momentum from microscale molecular diffusion to produce a macroscopic sideways thrust. This remarkable and fundamental discovery has implications for transport processes in regions of varying fluid density, such as the ocean pycnocline, and wherever there is a temperature difference between immersed objects and the surrounding fluid.

Funding for our research on stratified flows comes from the NSF.


Sailing on Diffusion

When a density-stratified fluid encounters a sloping boundary, diffusion alters the fluid density adjacent to the boundary, producing spontaneous flow. We have found that diffusion-driven flow can be harnessed as a remarkable means of propulsion, acting as a diffusion-engine that extracts energy from microscale diffusive processes to propel macroscale objects. This mechanism has implications for a environmental systems. [read the paper]

Relevant Publications

  1. Blanchette, F., Peacock, T. and Bush J.W.M., "The Boycott effect in magma chambers," Geophysical Research Letters, 31, L05611 (2004). [link]
  2. Peacock, T., Stocker, R. and Aristoff, J., "An experimental investigation of the angular dependence of diffusion-driven flow," Physics of Fluids, 16, 3503-3505, (2004). [link]
  3. Peacock, T., Blanchette, F. and Bush J.W.M., "The stratified Boycott effect," Journal of Fluid Mechanics, 529, 33-49 (2005). [link]
  4. Heitz, R., Peacock, T. and Stocker, R., "Optimizing diffusion-driven flow in a fissure," Physics of Fluids, 17, Art. No. 128104 (2005). [link]
  5. Yick, K.Y., Stocker, R. and Peacock, T., "Microscale Synthetic Schlieren," Experiments in Fluids, 42 (1), 41-48 (2007). [link]
  6. Blanchette, F., Peacock, T. and Cousin, R., "Stability of a stratified fluid with a vertically moving sidewall," Journal of Fluid Mechanics, 609, 305-317 (2008). [link]
  7. Yick, K.Y., Torres, C.R., Peacock, T. and Stocker, R., "Enhanced drag of a sphere settling in a stratified fluid at small Reynolds number," Journal of Fluid Mechanics, 632, 49-68 (2009). [link]
  8. Allshouse, M.R., Barad, M.F. and Peacock, T., "Propulsion generated by diffusion-driven flow," Nature Physics, 6, 516 (2010). [link]
  9. Mercier, M., Doyle, B.P., Ardekani, A. and Peacock, T., "Convection driven propulsion," in preparation.


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