Higher-order turbulent statistics of submerged wall jet over hemispherical macro-rough boundary: Insights from third-order moments, turbulent kinetic energy and length scales

Abstract

This study investigates, for the first time, turbulence in a submerged wall jet over a macro-rough boundary, emphasizing third-order moments, turbulent kinetic energy (TKE) field and budget, and the evolution of turbulent length scales using the instantaneous velocity data captured by Acoustic Doppler Velocimeter or Vectrino. Negative third-order moments in the jet outer layer and inner circulatory flow layer indicate downward and upstream fluxes of Reynolds normal stresses with deceleration. In the jet inner and reverse flow layers, positive values represent upward and downstream fluxes with substantial acceleration, reflecting inward and outward interaction events. Time-averaged TKE field indicates significant fluctuations in all three velocity components near the macro-rough boundary and along the null streamwise velocity line. Near-bed TKE production is higher, decreasing to the edge of jet inner layer, then peaks at maximum Reynolds shear stress. TKE dissipation steeply increases from the boundary, decreasing after the null-point of Reynolds shear stress. Variation of Taylor microscale and Kolmogorov length scale reveals that the Kolmogorov length scale follows similar trends but with smaller magnitudes, ranging from 0.0075 to 0.05 times the Taylor microscale.