by Rosalind O’Brien
“Turbulence is the graveyard of theories,” according to the renowned physicist Hans W. Liepmann, but scientists haven’t given up yet. Based on a turbulence lecture given by Prof. Mark Rast at the Laboratory for Atmospheric and Space Physics last Wednesday, it’s at least going to be a full and interesting graveyard.
Turbulence, in this context, is a specific physical phenomenon that describes the chaotic motion that can occur in fluids—both liquids and gases—when their molecules collide. Although many of us are unaware of it, turbulence occurs all around us, all the time.
The air behind an airplane and the water in an eddy are turbulent; they move chaotically at many scales, from those that humans can see and feel, all the way down to individual molecules.
Why does this matter? Rast provided plenty of reasons. Turbulence is why your car uses more gas when you go faster. When you’re driving, your car is slicing through the air in front of it. The faster you drive, the more difficult it is for air to converge immediately behind your car. This creates a sort of vacuum near your bumper, where air is moving chaotically, sucking your car backward ever so slightly. In other words, turbulence causes drag. Turbulence is therefore a very relevant concept in the automotive industry—it has literally shaped our cars. Continue reading