ON THE FLUX OF EDDY ENERGY IN SMALL-SCALE TURBULENT MOTION

Abstract

The irreversibility of the second law of eddy thermodynamics, developed by Blackadar, depends in part on the fact that the mean flux of eddy energy relative to a surface moving with the mean fluid motion is in the direction of decreasing eddy energy. The seemingly prevalent ambiguity in the definition of this relative flux of eddy energy is discussed, and a definition consistent with other meteorological concepts is presented. Data from the published results of several small-scale turbulence experiments are re-analyzed in an attempt to substantiate the hypothesis. In addition, an experiment involving an axially symmetric, low speed, free jet of air is briefly described, and the data from this jet are fitted to an idealized model in order to simplify the study of the relative flux. It is found that in all the cases tested the relative flux has, in general, the same sign as the negative eddy energy gradient. The apparent violations of the hypothesis can be explained as being due to: (1) the assumptions on which the experiments are based, (2) the relatively crude techniques employed in the present re-analysis of the experimental data, and (3) observational bias which may be inherent in the experiments.