Coherent Fine Scale Eddies in Turbulent Shear Flows and It’s Relation to Anisotropy

Abstract

The relation between coherent fine scale structure and anisotropy of turbulence is investigated by using DNS data of turbulent mixing layers and turbulent channel flows. These turbulent flows include tube-like fine scale eddies which are commonly observed in homogeneous isotropic turbulence (Kerr, 1985; She et al., 1990; Vincent and Meneguzzi, 1991; Jimenez et al., 1993; Tanahashi et al, 1996; Tanahashi et al., 1997a). In turbulent mixing layers, large scale structures which were found out by Brown and Roshko (1974) are composed of coherent fine scale eddies (Tanahashi et al., 1997c; Tanahashi et al., 1998). In turbulent channel flows, well-known streamwise vortices possess the same feature as the coherent fine scale eddies (Tanahashi et al., 1999a; Tanahashi et al., 1999b). Characteristics of fine scale eddies in turbulent mixing layers and turbulent channel flows coincide with those in homogeneous isotropic turbulence: the most expected diameter and maximum azimuthal velocity are about 10 times of Kolmogorov micro scale (η) and 0.5 times of r. m. s. velocity fluctuation (u′ rnts ). However, global characteristics of turbulence statistics are quite different in these flow fields. In this study, the origin of these difference is discussed from a viewpoint of the coherent fine scale eddies in turbulence.KeywordsInclination AngleFine ScaleIsotropic TurbulenceStreamwise VortexTurbulent Channel FlowThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.