Fluid turbulence

The swirling motion of fluids that occurs irregularly in space and time is called turbulence. However, this randomness, apparent from a casual observation, is not without some order. Turbulent flows are as abundant in nature as life itself, and are pervasive in technology. They are a paradigm for spatially extended nonlinear dissipative systems in which many length scales are excited simultaneously and coupled strongly. The phenomenon has been studied extensively in engineering and in diverse fields such as astrophysics, oceanography, and meteorology. A few aspects of turbulence research in this century are briefly reviewed, and a partial assessment is made of the present directions.