Baffling Fluid Dynamics

hurricaneDuring my student days, one of the most obviously complicated and beyond-comprehension modules was that on fluid dynamics. It’s not surprising that it was complicated and beyond comprehension, the way fluids (gases and liquids by definition) move is not simple.

There is no single, straightforward equation that can describe the flow of water cascading down waterfall. No clear-cut algorithm can determine exactly how oil will flow in an Alaskan pipeline. Mathematics and science struggle to predict the precise path of hurricanes and tornadoes. And, even tracking a water drop trickling down the back of Jeff Goldblum’s hand is off-limits. And, if you’ve ever tried to explain to a child how a plane becomes airborne and once at altitude doesn’t just fall out of the sky you will know that nothing about fluid mechanics is ever easy.

Of course, there are equations that describe fluid motion and while some of these are incredibly sophisticated they are far from perfect. There are the Bernouilli equations, for instance, which students (and professors) of the physical sciences struggle over to this day.

niagara-fallsUnderstanding how fluids move may seem trivial to the uninitiated if all it were about was predicting which way a water drop will fall. But, my allusion to hurricanes, planes and pipelines hopefully hints at just how important understanding fluid mechanics is. Fluid mechanics is a matter of life or death. A rather prosaic-sounding research paper entitled “Analytical and numerical analysis of the liquid longitudinal sloshing impact on a partially filled tank-vehicle with and without baffles” is testament to this fact.

At first glance, I have to admit I thought it was about improving efficiency at vehicle filling stations, but co-author of the paper Marc Richard of the Department of Mechanical Engineering, at the University Laval, in Québec, Canada, explained that it’s about improving the safety of tanker trucks. The kind of heavy-goods vehicles that weigh several tonnes, and carry highly combustible liquids such as petroleum, volatile and toxic organic solvents, and liquid food stuffs.

Picture the scene, it’s a wet and foggy night, a truck driver pulling a half-load of product from factory to outlet, takes a bend too quickly, swerves to avoid an oncoming vehicle and in the dazzling glare of headlights and spray veers off the road heading for a ditch.

The thousands of litres of liquid sloshing around in the half-filled tank follow all the right equations of fluid mechanics and some of the wrong ones. The combined momentum of those billions upon billions of organic molecules attempt to shove the truck and its tank-trailer one way, while the dwindling friction between wheels and wet road attempt to shove it another.

oil-tanker-crashThe inevitable outcome of this fluid reaction is a truck spinning out of control and overturning is it smashes into the ditch. The endpoint will depend on whether the truck was transporting an inflammable, volatile, and toxic load or full-fat cola.

Marc Richard and colleagues Messaoud Toumi and Mohamed Bouazara of the University of Quebec at Chicoutimi, want to inhibit this kind of out of control fluid mechanics. They are investigating the design of in-tank baffles that can smooth the sloshing of the fluid within. Whether a tanker truck goes out of control on a wet and foggy night, when a tire blows, or in a vehicle collision, these baffles will make the motion of the liquid load that much more predictable and perhaps give the driver a split second in which to recover control averting disaster.

At this point it would be easy to wax lyrical about the moral of the tale and persuade students everywhere to persist with their fluid mechanics studies. However, I suspect that no amount of persuading would encourage more than a few to consider hydrostatic pressure, incompressible fluids, and orifice baffles as anything but beyond comprehension.

Research Blogging IconM. Toumi, M. Bouazara, M.J. Richard (2008). Analytical and numerical analysis of the liquid longitudinal sloshing impact on a partially filled tank-vehicle with and without baffles International Journal of Vehicle Systems Modelling and Testing, 3 (3), 229-249