Flow: Nature's Patterns: A Tapestry in Three Parts
Format: PDF / Kindle (mobi) / ePub
From the swirl of a wisp of smoke to eddies in rivers, and the huge persistent storm system that is the Great Spot on Jupiter, we see similar forms and patterns wherever there is flow - whether the movement of wind, water, sand, or flocks of birds. It is the complex dynamics of flow that structures our atmosphere, land, and oceans.
Part of a trilogy of books exploring the science of patterns in nature by acclaimed science writer Philip Ball, this volume explores the elusive rules that govern flow - the science of chaotic behavior.
a ﬂuid is pumped into a rotating tank so as to mimic the zonal-jet structure. Organized vortices arise spontaneously and persist in the ﬂow. As the shear ﬂow gets stronger, the number of vortices decreases from ﬁve (a) to one (e). The positions of the vortices are shown schematically in the images on the lower right, for clarity. (Photos: Harry Swinney, University of Texas at Austin.) as Marcus had found. This same process has been seen on Jupiter itself: as they passed the planet in the early
afford. ‘At other times’, Bandello avers, ‘two, three or four days would pass without his touching the fresco, but he would remain before it for an hour or two at a time merely looking at it, considering, examining the ﬁgures.’ ‘Oh dear, this man will never do anything!’, Pope Leo X is said to have complained. As his sketchbooks attest, lengthy and contemplative examination was his forte. When Leonardo looked at something, he saw more than other people. This was no idle gaze but an attempt to
been seen by the physicist Atsunari Katsuki of Osaka University in Japan and his coworkers in experiments on the formation of artiﬁcial dunes. Dunes are usually too big and slow-forming to study in the lab, but Katsuki and his colleagues mimicked the process by suspending sand in ﬂowing water, which carried the grains down a ten-metre trough. This produced barchan-shaped dunes a few centimetres in size. Just like real dunes, these miniature versions moved gradually down the trough, horns ﬁrst
a single direction (d), or circulate in a hoop (e). (After Couzin and Krause, 2002.) 138 j NATURE’S PATTERNS: FLOW Fig. 5.7: Toroidal group motion is surprisingly common. It has been seen, for example, in ﬁsh (a), and slime moulds (b). (Photos: a, Copyright Norbert Wu; b, Herbert Levine, University of California at San Diego.) FOLLOW YOUR NEIGHBOUR j 139 in order to breathe; the torus allows them to do that without actually travelling anywhere. Moving in collective rather than individual
The question is whether or not the resulting disturbance of the ﬂow will gradually die away, and if so, how quickly. That is an important distinction, because the difference between smooth and turbulent ﬂow can be crucial in an industrial context. In turbulent ﬂow, the ﬂuid becomes strongly mixed up. And turbulence in pipe ﬂow can hinder the passage of the ﬂuid: the eddies, you might say, get in the way, reducing the overall ﬂow rate. This may cause pressure INTO THE MAELSTROM j 169 Fig. 6.2: