All turbulent flows of fluids have common characteristics such as irregular motion and dissipation. A solid grasp of turbulence can allow engineers to reduce aerodynamic drag on aircraft and exploit its beneficial effects by accelerating mixing and combustion. However, it is also necessary to comprehend the flow of blood in the heart, especially in the left ventricle when the movement is particularly swift. The description of turbulence is based on the assumption that flow variables satisfy the Navier–Stokes equations. In theory, these equations reveal the velocity and pressure of a fluid rushing by any point near an object's surface. The focus of the 'Control of turbulence' (COT) project was the relevance of unstable solutions of the Navier–Stokes equations and their role as building blocks of turbulence. COT researchers succeeded in finding a series of travelling wave solutions (TWS). Such solutions were believed to be relevant for the appearance of turbulence at a Reynolds number of around 2 000. The researchers quantified and confirmed the role of such structures by converging different states of wall-bounded flows observed in experiments to TWS. Another focus of the COT project was turbulence control. By exploiting insights into turbulence-sustaining mechanisms, COT researchers demonstrated that some TWS correspond to turbulence onset at a larger Reynolds number. As a consequence, the onset of near-wall turbulence can be delayed, for example by regulating pressure with wall suction. As more insights are gained into fluid dynamics, COT hopes to be able to move beyond predicting the effects of turbulence to actually controlling them. Such control can have enormous benefits for the aerospace industry, as a 10 % reduction in the drag of commercial airliners could yield a 40 % increase in airlines' profits.
Turbulence, turbulence prediction, aerodynamic drag, aircraft, Navier-Stokes equations, travelling wave solutions, Reynolds number, wall suction