Spanwise Streaky Structure and Macroturbulence in Open-channel Flows

Abstract

In order to reveal the interrelation between the bursting phenomenon occurring originally in the wall region and the macroturbulence such as kolk-boils and the cellular secondary current, which are observed in the outer region of an actual river, the present study has examined the spanwise spatial structures of open-channel flows with and without the cellular secondary current which was created artificially. A new conditional averaging technique, whereby the signals of a sampling probe are weight-averaged by the sorted instantaneous Reynolds-stress signals of a detection probe, has been used to evaluate the mean spanwise streaky spacings throughout the flow depth. The direct effect of the cellular secondary current on the bursting motion was not recognized. It was suggested that the coherent structures of an open-channel flow would indicate the doublestructure of turbulence, in which both the bursting and macroturbulence coexist self- consistently.