Planar intrusions from a source

We experimentally investigate the structure and evolution of planar, inertia-dominated intrusions from a constant source into a linearly stratified ambient. The source is either a negatively buoyant plume, or a jet situated at the level of neutral buoyancy. Intrusions generated by plumes form self-similar wedges, with a constant thickness at the source of (2.5+/-0.3)(Q/N)^1/2 and the wedge lengthening in time t as (0.32+/-0.03)(NQ)^1/2 t, where N is the buoyancy frequency and Q is the areal supply rate. Intrusions generated by jets are qualitatively different and not self-similar. Immediately adjacent to the source, they thicken significantly through a turbulent hydraulic jump. Beyond this is a gently thinning region that lengthens over time. The profile of both regions appears steady once established. Ahead of the thinning region is a more rapidly tapering nose leading to the propagating front. The area of the intrusion increases as a power law in time, with an exponent between 0.6 and 0.7, suggesting that the significant entrainment occurring in the hydraulic jump decays over time. The fronts also propagate as power laws with similar exponents. We compare our experimental observations with predictions from an intrusive shallow-water model. The model can rationalise many of the observed behaviours, but does not provide an accurate description of the profiles.