Submerged wall jet on a macro-rough boundary: turbulent flow characteristics and their scaling laws

Abstract

Abstract This study presents the turbulence characteristics and the scaling laws in a horizontal submerged wall jet on an array of hemispherical macro-rough elements forming an open-channel boundary. The flow field was measured by an acoustic Doppler system, called Vectrino. The turbulence characteristics on a macro-rough boundary, being different from those on smooth boundary, are discussed from the perspective of decay of the local-peak parameters, similarity, and growth of the length scales. The vector plots, streamwise velocity flow field, and the jet velocity variations show that the decay rate of jet velocity in a submerged jet on a macro-rough boundary is initially sharp and then gradually drops down to become independent of streamwise distance. The growth rate of the jet boundary layer thickness is initially slow and then becomes fast as it tends to reach the free surface. On the other hand, the plots of the Reynolds shear stress and turbulence intensities, and the variations of their local-peak magnitudes reveal the gradual damping of these parameters with the streamwise distance. These results encapsulate the recovery of a submerged jet on a macro-rough boundary to become an open channel flow. The most important outcome is that the streamwise velocity, Reynolds shear stress, and turbulence intensities in the fully developed zone are found to be self-similar when the velocity is scaled with the local-peak velocity against jet half-width, and the Reynolds shear stress and turbulence intensities are scaled with their respective local-peak magnitudes against half-width of Reynolds shear stress. The boundary shear stress diminishes with an increase in streamwise distance.