Finite time blowup for an averaged three-dimensional Navier-Stokes equation - "[Terence Tao] has shown that in an alternative abstract universe closely related to the one described by the Navier-Stokes equations, it is possible for a body of fluid to form a sort of computer, which can build a self-replicating fluid robot that, like the Cat in the Hat, keeps transferring its energy to smaller and smaller copies of itself until the fluid 'blows up.' " [1,2,3] (previously)
A Beginner's Guide to Aeronautics, a web-based textbook brought to you by the folks at NASA. [more inside]
Reversible flow! In the 1960s, the National Committee for Fluid Mechanics Films produced a series of films for education in fluid mechanics. This clip is part of "Low Reynolds Number Flow"; you can find the entire collection streamed here. Interesting demonstrations abound. (1st link is QT; rest are RealPlayer.)
The Navier-Stokes equations constitute the fundamental equations that describe fluid mechanics, and are used everywhere from atmospheric science to airplane design. Proof of the existence of a smooth solution to the Navier-Stokes equations in 3-dimensions is considered a challenging problem, so challenging that the Clay Math Institute has offered a million dollars to anyone who can do so. Has it been done? (More detailed explanation). (via)
Gallery of Fluid Dynamics. 'One of the most attractive features of fluid mechanics is the beauty of the flows one encounters. Whether one is observing vortex streets, the potential flow around an airfoil or body, shock refraction or diffraction, or waves breaking on a beach the aesthetic appeal of fluid mechanics is impossible to deny. '