Author(s): H. I. S. Nogueira
Linked Author(s): A.A.S. Nogueira
Keywords: Density currents; Mass balance; Entrainment; Image analysis
Abstract: In the governing equations of density currents, namely in the total mass balance equation, the entrainment rate of the ambient fluid through the upper interface becomes an explicit or source term requiring a closure model. The entrainment rate may be generally modelled as a function of the current longitudinal front velocity and it is usually evaluated through empirical relations. The aim of the present work is to experimentally investigate the entrainment of ambient fluid into unsteady density currents performed by lock-exchange release of saline water. The experiments were conducted in a 3.0 m long, 0.20 m wide and 0.30 m deep transparent Perspex flume, with horizontal smooth bed, and recorded with a 25 Hz CCD camera under controlled light conditions. An image analysis technique was applied to estimate time-space varying density of the current using dye concentration as a tracer. Temporal and spatial evolution of the current height and depth-averaged density, and temporal evolution of the front position, front velocity, mass balance and entrainment rate are thus assessed and discussed. The relation between entrainment rate and front velocity seems to converge asymptotically to a constant value.
Year: 2011