The Rate of Expansion of a Confined, Submerged Jet

The expansion of a confined, submerged jet was examined experimentally for a range of jet Reynolds numbers (in the turbulent regime) and geometries, by measuring the wall pressure profile. Simple dimensional analysis of the experimental and numerical results showed that the flow characteristics were unique functions of the jet to column diameter ratio and were independent of the jet Reynolds number. Computational fluid dynamics modelling of the flow system was carried out to support the experimental data and to gain further insight into the flow patterns. The radial expansion of the jet, predicted by numerical simulation, showed that the initial expansion of the jet was almost linear and could be approximately modelled as a free jet. The velocity profile was close to Gaussian and was self-preserving throughout the recirculating region. Flow visualisation studies of a submerged water jet revealed a high level of instability within the recirculating region and the jet was observed to flap due to the Coanda effect.