STRUCTURE OF REYNOLDS SHEAR-STRESS IN THE CENTRAL REGION OF PLANE COUETTE-FLOW

The structures and mechanisms for maintaining a high Reynolds shear st ress throughout the core region of plane turbulent Couette flow were e xamined by means of databases originating from a direct numerical simu lation. At the relatively low Reynolds number considered, the mean she ar rate and some one-point statistics exhibited a non-negligible varia tion in the core region, which conflicted with the postulated homogene ity. The slope of the mean velocity profile was below a theoretically established lower bound for the limit of infinite Re. Analysis of the time-averaged and structural information obtained by conditional sampl ing showed that mean shear generation and velocity-pressure gradient c orrelations played a crucial role in the generation and annihilation o f the Reynolds shear stress. it was moreover observed that strong, ver y localized velocity fluctuations in the wall-normal direction were es sential in both processes. A simple conceptual model was proposed to e xplain the physical significance of the pressure field associated with quadrant 2 events.