Convection

When there is a temperature difference between the top and bottom of a fluid, hot fluid tends to rise, and cold fluid then comes down again. At low temperature differences (characterized by a low dimensionless Rayleigh number) a regular pattern of hexagonal Bénard convection cells is formed (see page 377). But as the temperature difference increases, a transition to turbulence is seen, with most of the same characteristics as in flow past an object. A cellular automaton model can be made by allowing particles with more than one possible energy: the average particle energy in a region corresponds to fluid temperature.