At lower speeds, the flow is continually calm and linear above wings or in pipes, as if thin layers of air or liquid were sliding above each other. However, if the flows get faster, they exhibit the first signs of turbulence, and so-called turbulent patches are created, according to Hof.
These turbulent patches move as localized fronts with a consistent size through the system. The same phenomenon exists with nerve fibers through which electrical stimuli (action potential) flow, and as roaming wave stimulation in heart tissue. However, they do not further increase in contrast to the turbulent patches in flows.
The researchers inspected the phenomenon in flow experiments as well as in computer simulations, and were ultimately able to put together a mathematical model enabling them to calculate which state arises at which flow rates. One practical application of these findings would be for oil pipelines. Pumping costs amounting to billions of dollars are mainly due to the friction losses resulting from turbulence.