Author(s): D. Hurther; U. Lemmin
Linked Author(s): Ulrich Lemmin
Keywords: Shear stress dynamics; Conditional statistics; Conditional sampling; Coherent structures; Turbulent energy budget
Abstract: 3D quasi-instantaneous velocity profiles are taken at the center of a uniform, turbulent, open-channel flow over a rough bed. A cumulant discard method is applied to describe the statistical properties of the covariance terms u′w′and v′w′relative to their time means. Conditional statistics and conditional sampling are used to compare the theoretical and experimental relative shear stress contributions from quadrants in the longitudinal and transverse planes. The results in the (u′, w′) section show the presence of outward interactions (quadrant I), ejections (quadrant II), inward interactions (quadrant III) and sweeps (quadrant IV) with dominance in quadrant II and IV. The transverse quadrant distribution of fractional v′w′events is characterized by a quasi uniform repartition over the transverse plane. A simple linear relation between the third order cumulants of the two probability densities leads to an expression for the turbulent kinetic energy flux indicating its strong dependence on the bursting process. Finally the positive and negative contributions to the stress production are compared with the transport term evaluated from the third order moment of u′.
Year: 1999