Fluids, such as air and water, are all round us. They are responsible for many daily phenomena. For example, they are the reason why birds can fly and fish can swim. On much larger scales, motion and phase changes of fluids lead to formation of weather phenomena, such as storms and hurricanes. The following figure shows a few fluid-related phenomena across nine scales from micrometers to kilometers.
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Fluids exhibit rich and seemly self-contradictory behaviors, as poetically illustrated by Laozi in Tao Te Ching:
Under heaven, nothing is more soft and yielding than water,
yet, for attacking the solid and the strong, nothing is better; it has no equal .
To understand these fluid-related phenomena is not only an intellectual challenge but also has far reaching implications for many practical issues.
In our group, we use well-controlled laboratory experiments complemented with theoretical and numerical models to study a wide range of fluid dynamics problems. Beyond "simple fluid", we are also interested in other fluid-like systems, such as colloids, granular materials, and bacterial suspensions.