Spatially averaged turbulent stress and its partitioning

Double averaging of the fundamental flow equations is an attractive methodology for investigating spatially heterogeneous flows. The resulting double-averaged equations can be used as a framework for development of turbulence models. In order to fully explore the potential of such models the stress terms that appear in the momentum equation as a result of each averaging step needs to be parameterised. We investigate the stress terms resulting from the double-decomposition of instantaneous velocity. The experimental values of these stress terms were determined from the laboratory experiments involving PIV measurements of shallow open channel flows over rough beds. Special attention is paid to the two terms that together form the spatially averaged turbulent stress, which have so far not been reported in the literature.