Vorticity and Turbulence in the Wake of a Bridge Pier

Abstract

Dissipation rates of turbulence kinetic energy (TKE) epsiv and enstrophy zeta2 are reported in a high Reynolds number turbulent wake. Previous turbulent wake observations have been made in laboratory experiments with relatively low Reynolds number flows O (103). Results presented here are from a set of rare field observations of vorticity and turbulence in a turbulent wake with a high Reynolds number O (107). The turbulent wake was formed by an unsteady strong tidal current interacting with a bridge pier. Measurements were taken mostly in the intermediate wake, i.e., 10 les x/d les 60, where x is the downstream distance and d is the width of the bridge pier. Both epsiv and zeta2 show a similar downstream decay rate that is faster than that predicted by the self-preservation similarity in the far wake. The theoretical relation epsiv = nuzeta2 for high Reynolds number flow is confirmed by field observations. The magnitudes of the vertical and horizontal components of enstrophy do not differ significantly. The turbulence internal intermittency is ~ 0.2, estimated from autocorrelation coefficients of enstrophy; this value is close to that reported previously in turbulent wakes and jets.