TURBULENCE WITHIN INERTIA-BUOYANCY BALANCED AXISYMMETRICAL INTRUSIONS

Data from two detailed field experiments were used to investigate the turbulence within inertia-buoyancy balanced axisymmetric intrusive gra vity currents entering nearly quiescent stratified water bodies. The i ntrusions were generated by energetic point source bubble plume system s installed within different freshwater reservoirs, and the mixing act ivity was recorded with microstructure profilers. Close to the bubble plume, the intrusions were found to be very turbulent. The turbulent a ctivity within the intrusions was observed to decay most rapidly in th e intrusion core, but the shear at the upper and lower boundaries of t he intrusions maintained the turbulence in these regions for along dis tance. The results showed that the turbulence began with a length scal e equal to the maximum sustainable overturn length for internally gene rated shear and hence a turbulent Froude number near unity. As the int rusions moved away from the generation region, the Froude number remai ned near unity, but the Reynolds number decreased with distance; the s hear generated by the intrusion thus sustained an active turbulence fi eld, albeit with ever-decreasing length scales.