On Time Scales in a Particle-Laden Turbulent Flow

Abstract

1 The v arious time scales as well as their relationship , considering the effects of flow 's inhomogeneity and anisotr opy in a particle -laden turbulent channel flow , are investigated . Numerical modeling is performed using the method of large eddy simulation coupled with Lagra ngian particle trajectory m ethod, which is valuated well compared with previous DNS results. Diffe rent flow characteristic time scales are compared with each other. Correlation functions of fluid -phase velocity, particle -phase velocity and fluid -phase velocity seen by particles are calculated to obtain Lagrangi an and Eulerian integral time scales. Lagr angian integral time scales of fluid velocity increase with the distance from the wall, whereas Eulerian integral time scales increase slightly firstly to about y + =10 and then decrease to the channel central plane . The n ear -wall Lagrangian integral time sc ales of fluid velocity are almost the same as those seen by particle s, whereas, close to the central plane of the channel , the former are longer than the latter. The streamwise Lagrangian integral time scales are the longest for particles with very small S tokes number, but the spanwise ones are the longest for particles with very large Stokes number . With increasing Stokes number, Lagrangian integral time scales of flui d velocity seen by particles become isotropic in the channel central region. The ratio o f diagonally averaged Lagrangian integral time scale to the moving Eulerian time scale is between 0.4 and 0.7.