Sreenivasan DMS9729251 "Turbulence: Challenges for the 21st Century" An International Conference Wind gusts and roaring fires, tornadoes and hurricanes, flows around ships and aircraft, flow through pipelines, pumps, turbomachinery, as well as arteries, are some examples of turbulent motion of fluids. Our ability to describe and predict turbulent phenomena strongly impacts such diverse fields as environmental pollution, weather prediction, commercial chemical processes, aircraft and ship design, ocean dynamics, and astrophysics. Turbulence is thus a subject of great importance and demands serious attention. Yet, it is one of the poorly understood subjects, despite about hundred years of serious research. Why is this so? It is trite but true to say that it is a very difficult subject. The difficulties stem from the fundamentally complex dynamical characteristics of turbulence including, for example, strong nonlinearity, the simultaneous presence of a large number of interacting degrees of freedom across a wide range of spatial scales, marked departure from statistical equilibrium, and so forth. More than $10^{18}$ degrees of freedom can be excited in turbulent flows typical of atmospheric phenomena. This makes full computer simulation of such flows impractical. Experimental studies have also suffered because of approximations such as Taylor's hypothesis and the use of one-dimensional surrogates for three-dimensional quantities. A confluence of important advances has occurred in the last decade: new experimental tools have emerged, and enabled direct measurement of spatio-temporal fields of turbulence, and new parameter ranges are being explored in experiments by harnessing air at high pressures or unconventional fluids such as helium. Direct numerical simulation has become a powerful tool for the study of turbulence. Recent improvements in computer memory and speed, especially the availability of we ll-integrated massively parallel machines, have made computer simulation a useful complement to laboratory experiments. In addition, greater insights into the behavior of nonlinear partial differential equations are being acquired rapidly. Together, these advances have had a qualitative impact on the understanding of turbulence dynamics, and on the development of working models in engineering practice. Particular progress has been achieved in the case of passive admixtures (such as dye, water vapor, pollutants which are mixed by turbulence, but do not feed back to the turbulent motion itself). For example, theoretical predictions have been made for anomalous scaling in a class of passive admixtures. These predictions are in turn supported by direct numerical simulation. To assess these recent advances and define, where possible, new directions for the field, a conference is being organized at Los Alamos between the 25th and 28th of May 1998. The conference is being supported by the National Science Foundation and the Los Alamos National Laboratory. The specific goal of the conference is to provide an opportunity for scientists world-wide to communicate recent critical advances in fundamental studies and engineering applications of fluid turbulence, and to foster further development of this broad field of nonlinear science.
