Instability of horizontal dense jets at low and moderate Reynolds number

Dongdong Shao, Dingyong Huang, Baoxin Jiang, Adrian W. K. Law

Wednesday 1 july 2015

11:45 - 12:00h at Antarctica (level 0)

Themes: (T) Special session, (ST) Marine outfall system

Parallel session: 9D. Special Session: Marine Outfall System

Unlike horizontal buoyant jet in the turbulent regime, the laminar horizontal buoyant jet has been found to exhibit peculiar behaviour of unstable nature, e.g., bifurcation in the form of a vertical secondary plume deriving from the primary jet, due to the unstable stratification on one interface between the jet and the ambient fluid. However, the majority of the existing studies were focused on the low Reynolds number regime (Re<500), whether the jet instability will persist into the transitional regime (500<Re<2000) remains an open question. In this study, we explored the structure and stability, i.e., the tendency to bifurcate, of horizontal dense jets at low and moderate Reynolds numbers in the laboratory. Planar Laser Induced Fluorescence (PLIF) was used for flow visualization as well as quantitative concentration measurement. Three different flow patterns characterised with distinctive structures, namely, primary jet with vertical secondary plume, primary jet with pseudo secondary jet, quasi-turbulent horizontal buoyant jet, were identified from longitudinal and cross-sectional images, together with their distribution on the Re-Fr map. The impact of the instability on the jet mixing characteristics, e.g., the decay of the maximum concentration along the jet axis, the cross-sectional concentration distribution at different downstream locations, etc, was further analyzed using the processed PLIF data. The results provide new insight on the structure and stability of horizontal dense jets in the laminar and transitional regimes.