skip to content

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 Natural Convection

When a homogeneous fluid is heated (or cooled) at an inclined surface, a boundary-layer flow develops along the surface that is driven by buoyancy effects due to the change of density with temperature. We have designed a triangular wedge immersed in a fluid with one of his boundaries being a heated plate, and showed that this macroscopic object moves at a constant speed when heating is on. We also predict the speed of the wedge by balancing the drag with the propulsion force obtained by the analytical description of the boundary-layer laminar flow. This effect has potentially widespread application to topics as diverse as bioengineering, microfluidics and geosciences. A detailed report of this study has been published in Physical Review Letters. [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., Ardekani, A., Allshouse, M. R., Doyle, B., and Peacock, T., "Self-Propulsion of Immersed Objects via Natural Convection," Physical Review Letters, 112, 204501 (2014).[link]


back to top