University of Illinois at Urbana-Champaign. Water Resources Center
Abstract
This work was concerned with an improved and more practical understanding of particle motion in a turbulent fluid field. It is felt that such an increased understanding has been achieved both in an analytical and in an experimental sense. Analytically, a theory simplified by the restrictive constraints of isotropy and Stokesian drag has been developed. Assumption of a reasonable particle energy spectrum allowed calculation of various statistical quantities important in the determination of the particle's turbulent motion. By such an analysis three characterizing parameters were found. Two describe inertial effects due to the particle's size and density. They were found to be of prime importance in the determination of the ratio of the particle's fluctuating velocity variance to that of the fluid. The crossing of the particle from one region of correlated fluid turbulence to another by virtue of its free fall velocity is described by the third parameters. This parameter was shown to be of particular importance in limiting the particle's velocity correlation. The two effects, of inertia and of free fall velocity, together act to determine dispersion. A well parameterized particle experiment was undertaken. Analysis of the particles' behavior in the turbulent flow gave a three dimensional characterization of their motion. In particular calculation of velocity variances, autocorrelations, and energy spectra were made. These measurements in conjunction with measurements on the turbulent fluid field allowed comparison between theory and experiment. Comparison of theoretical prediction to experimental observation showed good agreement provided the underlying assumptions inherent in the theoretical derivation were valid. Agreement suffered when these assumptions proved less valid. In particular non-Stokesian drag and anisotropic effects caused. disagreement between theory and experiment.U.S. Department of the InteriorU.S. Geological SurveyOpe
