Turbulence structures of wall-bounded shear flows found using DNS data

This work extends the study of the structure of wall-bounded flows using the topological properties of eddying motions as developed by Chong et al. (1990), Soria et al. (1992, 1994), and as recently extended by Blackburn et al. (1996) and Chacin er al. (1996). In these works, regions of flow which are focal in nature are identified by being enclosed by an isosurface of a positive small value of the discriminant of the velocity gradient tenser. These regions resemble the attached vortex loops suggested first by Theodorsen (1955). Such loops are incorporated in the attached-eddy model versions of Perry & Chong (1982), Ferry et al. (1986), and Ferry & Marusic (1995), which are extensions of a model first formulated by Townsend (1976). The direct numerical simulation (DNS) data of wall-bounded flows studied here are from the zero-pressure-gradient flow of Spalart (1988) and the boundary layer with separation and reattachment of Na & Moin (1996). The flow structures are examined from the viewpoint of the attached eddy hypothesis.