Turbulence within inertia‐buoyancy balanced axisymmetric intrusions

Abstract

Data from two detailed field experiments were used to investigate the turbulence within inertia‐buoyancy balanced, axisymmetric intrusive gravity currents entering nearly quiescent stratified water bodies. The intrusions were generated by energetic point source bubble plume systems installed within different freshwater reservoirs, and the mixing activity was recorded with microstructure profilers. Close to the bubble plume, the intrusions were found to be very turbulent. The turbulent activity within the intrusions was observed to decay most rapidly in the intrusion core, but the shear at the upper and lower boundaries of the intrusions maintained the turbulence in these regions for a long distance. The results showed that the turbulence began with a length scale equal to the maximum sustainable overturn length for internally generated shear and hence a turbulent Froude number near unity. As the intrusions moved away from the generation region, the Froude number remained near unity, but the Reynolds number decreased with distance; the shear generated by the intrusion thus sustained an active turbulence field, albeit with ever decreasing length scales.