Boston (MA) - A team of scientists affiliated with MIT's Mechanical Engineering department have solved a 100-yr old engineering problem. In 1904, a German physicst named Ludwig Prandtl mathematically solved the problem of flow separation in fluids. His work did have limitations, however, namely that it only worked in two dimensions and the air flow had to be very steady. MIT's new model expands Prandtl's research into three dimensions and unsteady streams of air. Plus, it has the added bonus of being experimentally verified.


Big savings add up

Such discoveries make big changes for regular people. They will pave the way for future plane, automobile and boat designs, those with less drag and greater fuel economy. Relatively small changes to normal automobile designs have already produced big savings in fuel economy. In large diesel trucks, for example, adding wind conforming fins and spoilers have shown increases in fuel economy of nearly 10%. MIT's method of reducing air drag could increase it another 10%.

In 2006, the United States consumed 20.7 million barrels per day of liquid petroleum. Increasing fuel efficiency by 10% (about 3 miles per gallon) would reduce the average consumer's annual fuel expense by $150 (at $4.00 per gallon) per car. It would save the entire consumer market an estimated $460 million each day ($168 billion per year).




Solving it in 3D

The problem MIT solved is probably one unknown to most people. And even when it's explained it's probably an unexpected effect. The example they give is an automobile going up and down hills, slowing down and speeding up all the while, then slowing much more to make a hairpin turn. In each of these cases, the air around the vehicle does not "keep up" with the car's changing velocity and directions. In fact, the air actually begins to pull away, or separate, from the car, increasing drag and decreasing fuel economy.

The same effects are present in golf balls, boats, airplanes and everything that interacts with fluidic surfaces, which physicists describe as being of both water and air types.


Paper published

Today's issue of Journal of Fluid Mechanics, and this month's Physics of Fluids, carry MIT's paper which outlines the new 3D model and explains experiments that were carried out to validate it.

The model was created by George Haller, a visiting professor at MIT, and experimentally confirmed by Thomas Peacock, an Atlantic Richfield Development Associate Professor.  It is a model which has overcome previous pitfalls.

Over the past century there have been numerous and vigorous efforts to solve this problem through a model which accurately predicted observable phenomena in 3D, and in unsteady air flows. This team's efforts are the first to succeed and the first to be published.


Baby steps

The team first created and published a model which operated on unsteady separations in the same two dimensions. This expanded on Prandtl's work by moving from his "very steady" requirement to a now unsteady flow of air.

Next, and building upon that research, the team created a 3D model which accurately reflects the real-world, observable effects we've all seen in documentaries and even on commercials. Things like cars driving through a short band of fog and producing a lot of turbulance as it goes around a corner, for example. Or, the smoke streams visible along the edge of an airfoil when in a wind tunnel.


Moving forward

The model they've created is not quite ready for the "prime time" of commercial applications. However, they have proven the theory does work and is experimentally validated. The next steps are to continue the research and produce a model which can be used in commercial endeavors.

Who knows, in ten years we might all be buying cars with fins on them again because the MIT model says it's really what we need.

Chemist

Sep 25, 2008 12:58     

Here's a good answer to my daughter's complaint about taking pre-calculus in high school. This is a mathematical triumph for the scientists and has the potential to benefit mankind as it moves forward...literally.
Greg George report abuse vote down vote up Votes: +7

MIT...

Sep 25, 2008 13:39     

Man what those people pump out... it's remarkable!
ubu report abuse vote down vote up Votes: +5

What is the significance?

Sep 25, 2008 22:23     

People have been solving 3D unsteady fluid flow computationally for years. I have no doubt that MIT is advancing the science, but is this just an evolutionary advancement or actually a revolutionary advancement as being portrayed by this article? I suspect that the significance is that a new model for simulating unsteady flow. With a fine enough grid, finite-difference, finite-volume, finite-element, etc. models can directly solve the Navier-Stokes equations for turbulent flow. The issue is that it would take years/ centuries for the model to finish for anything other than simple cases. Models are used to make assumptions about what is happening within the grid. I suspect that the MIT team has developed a better model, which is a good thing. However, to expect this to make anything other than incremental improvements to our understanding of fluid flow would be foolish. Without having access to a Journal of Fluid Mechanics, I don't know for sure. I do assume it is significant if you are in the field of fluid mechanics.

powervolume report abuse vote down vote up Votes: +0

Re: What is the significance?

Sep 26, 2008 05:45     

Only an incremental improvement? So if it's not a complete paradigm shift, we should ignore it? Any advance in the mathematics of fluid dynamics, even a small one (and this is actually a fairly large one), is extremely important to every human being on earth. Good job MIT. Keep up the good work.
Charles report abuse vote down vote up Votes: +2

Its very good...

Sep 26, 2008 06:40     

But its still very restricted in where it can be applied. Low Reynolds numbers and relatively steady flows. For instance, the transonic shock induced boundary layer separation (which is the No. 1 cause of lift independent drag on aircraft today) cannot be analysed using this approach.
Aerodynamicist report abuse vote down vote up Votes: +1

All Hail, Laminar Flow!

Sep 26, 2008 08:47     

Ah, this brings me back to the days of old, when Bernouli's Law and Laminar Flow were kings of Fluid Mechanics. I actually thought of becoming a Fluid Mechanic... I had read an ad in a comic book, "Become a Fluid Mechanic in 60 days!" Fluid mechanics is the study of gases and liquids at rest and in motion...and God knows, I had plenty of gas and liquids, especially after those college benders. "Yep, fluid mechanics make big bucks. Heavy bread. They're rolling in dough. They carry big wads of 10's and 20's in their pockets. A lot of MONEY. They drive Cadillacs and buy their wives minks. And they eat steak. "...but I digress. Seriously, This IS a significant research. Finding models to move through air and water without creating a drag is one those of those significant behind the scenes events that make out lives better.

Kayo report abuse vote down vote up Votes: +0

"not quite ready"

Sep 27, 2008 11:54     

Does this mean no one should use this model to improve aerodynamic efficiency yet? It seems like every little bit should help. BTW, I can't wait for fins to return to cars :)
Spych0 report abuse vote down vote up Votes: +1

Technical writing police

Sep 27, 2008 13:53     

""keep up" with the car's changing velocity and directions" Velocity includes direction, it's a vector.
Scott report abuse vote down vote up Votes: +0