Turbulent flow is characterized by very irregular and chaotic motions with a wide range of eddy scales so that unpredictability is an essential feature of such a flow. Since the velocity filed is very variable in time and space, it also has very high values of the vorticity. The large diffusivity of turbulent flows implies a high ability to mix properties efficiently, which is probably one of the most important characteristics of turbulent flow.
The various motions of the air in the earth's atmosphere, from a slight breeze in the surface layer up to general atmospheric circulation of planetary scale are turbulent. Turbulent, too, are the flows of the water in rivers, lakes, seas, oceans, and also the motions of gases in interstellar nebulae having an enormous scale many orders greater than the earth. Without turbulence and the mixing we would not have the same ocean that we do now, nor indeed the same climate.
Practically all flows in pipes encountered in technology and engineering are turbulent, e.g., in water-pipes, gas mains, petroleum pipelines, the nozzles of jet engines, etc.; and also the motions in the boundary layers over the surfaces of moving aircraft, ship, missile, submarine, etc.; in liquid or gas high-speed jets issuing from a nozzle, in the wakes behind rapidly moving rigid bodies - propeller blades, turbine blades, bullets, projectiles and rockets. Thus turbulence is literally all around us both in nature and in engineering devices using flows of liquids and gases; therefore its study is extremely important from the practical viewpoint.
Turbulent flows are also of great interest from a purely theoretical point of view as examples of nonlinear mechanical systems with a very great number of degrees of freedom. Although much is still unknown about turbulence, recent developments in nonlinear dynamics have lead to an understanding of the onset of turbulence, and the advent of the supercomputer has enabled better models of turbulent states to be developed. Experimental work has shown that the onset of turbulence occurs abruptly, and in face is characterized by so called "strange attractors" of nonlinear dynamics.
The only possibility in the theory of turbulence is a statistical description, based on the study of specific statistical laws, inherent in turbulent phenomena. Thus only statistical fluid mechanics, which studies the statistical properties of the ensembles of fluid flows under macroscopically identical conditions, can provide a turbulent theory. Increased understanding of turbulent flow is leading to advances in such as the design of better airplane wings and artificial heart valves, forecasting, climate theory, and ecology.
Current research thrusts include:
- Ocean Turbulence
- Vortex Instability of Surface Waves
- Internal Waves Turbulence
- Double Diffusive Convection
- Theory and Laboratory Study Wave-Turbulence Interactions, Wave Breaking
- Nonsteady Turbulent Boundary Layers of the Ocean and Atmosphere
- Small scale Air-Sea Interaction
- Influence of Surface Waves on the Atmospheric Turbulent Boundary Layer
- Small scale Interactions of the Water Body and the Atmosphere of the Inshore Zone
- Ship and Submarine Waves
- Ecosystem Modeling