The gist is that they've created a better theory of flow separation (roughly speaking, where a flowing fluid "tears loose" from a boundary surface of some sort to make a sheet of fluid that folds up and projects out into the main flow).
Their theory deals only with incompressible flow, so I'm not sure how much this would help aerodynamic simulations, but it's probably got lots of applications in hydrodynamics and industrial process simulation.
This is one of the reasons why I get most of my news these days through HN, and typically read the comments first. I get a concise summary and usually more interesting links to the original research.
Typically, incompressible flow is valid in gases for Mach numbers less than 0.3, so this is relevant for automotive aerodynamics and wind turbines, but not for turboprops, jet engines, compressors, gas turbines, and most airplanes.
They've derived exact mathematical expressions for the shapes and locations of those flow separations, and it sounded like the whole derivation was based on the assumption of incompressibility, so I'm not sure how extensible their approach is to compressible flow.
That said, it's totally true that you could use this sort of code in gasdynamics situations where the compressibility doesn't matter much, as you pointed out.
The experimental setup they validated their code with used three liquids -- Fluorinert, glycerol, and vegetable oil -- shearing past each other and the walls of a container while being stirred slowly. All incompressible, true, but perhaps chosen for experimental convenience rather than any problem with their theory's handling of compressibility.
It's fascinating science, but the one thing that it proves to me is that MIT has absolutely solved the science of the press release. They do a far better job than most other engineering schools that I know of at hammering the message (for any given message) home, over and over, in breathless prose.
The very fact that they've subtitled their magazine (" Technology Review") as "The Authority on the Future of Technology" is proof of that.
Hell, the fact that they've gone beyond press releases to printing up their own hagiographic magazine is proof of that.
I don't say this to be bitter - as someone for whom marketing does not come easy, I'm perpetually impressed by what a great job they do.
Their theory deals only with incompressible flow, so I'm not sure how much this would help aerodynamic simulations, but it's probably got lots of applications in hydrodynamics and industrial process simulation.
You can see the original papers at http://web.mit.edu/ghaller/www/papers.html.