Lagrangian statistics in turbulent channel flow.
Wang-Q; Squires-KD; Wu-X
Atmos Environ 1995 Sep; 29(18):2417-2427
A particle trajectory based (Lagrangian statistics) approach for analyzing eddies in fully developed turbulent channel flows applicable to analyzing the transport of smoke, solid particulates, and similar pollutants in the atmosphere was described. Lagrangian statistics were obtained for particles located in the viscous sublayer, the buffer layer, and the logarithmic layer of a turbulent channel utilizing a subgrid scale model that simulated large turbulent eddies. The subgrid scale model was made up of 5,000 fluid elements based on the filtered Navier Stokes equation. Single particle Lagrangian velocity autocorrelations and mean square particle dispersions were calculated for channel flows characterized by Reynolds numbers of 180, 1,000, 3,200, and 21,900. The Lagrangian velocity autocorrelations in the streamwise direction decreased most rapidly for particles that were initially in the viscous sublayer, followed by particles in the buffer layer and in the logarithmic layer. Mean square particle dispersions in the streamwise direction were larger than the spanwise component which was in turn larger than the dispersion in the surface normal direction. For short particle diffusion times, the mean square dispersion was proportional to the velocity variance. For long diffusion times, the dispersion was limited by the presence of the channel boundaries. This led to the fluid elements eventually becoming uniformly distributed throughout the channel. When the time scales of the Lagrangian statistics were compared to the traditional Eulerian time scales, the ratio of the Lagrangian to Eulerian time scales was found to be proportional to the reciprocal of the simulated turbulence intensity. The authors note that the results of these calculations agree with the results of direct numerical simulations and experimental data.
AENVEQ; NIOSH-Publication; NIOSH-Grant; Grants-other; Air-flow; Mathematical-models; Simulation-methods; Diffusion-analysis; Fluid-mechanics
Mechanical Engineering Univ of Vermont/state Agric Co Votey 209B Burlington, VT 05405
Other Occupational Concerns; Grants-other;
University of Vermont & St Agric College, Burlington, Vermont