Motion of Dense Thermals on Incline

Abstract

In this paper, results on the motion of two‐dimensional dense thermals descending on slopes of less than 5° are presented. The front propagation, concentration distribution, and internal structure of the thermals are investigated experimentally and analytically. Laboratory experiments are carried out in a 20‐m‐long water tank to determine the front velocity and the temperature field in cold, saline thermals. The similarity assumption is employed in the analysis of the results. The front velocities of the thermals agree well with analytical results, and the influence of the water depth at the source on the rate of advance of the front is insignificant. The similarity concept is shown to result in contradictions when applied to depth‐averaged parameters in the tail of the thermals. The internal structure of thermals is further examined by using laser‐induced fluorescence (LIP) flow visualization in a 1‐m‐long aquarium. The photographs show that three‐dimensional structures form at the front and engulf ambient fluid. The frontal part has oscillatory propagation of lobes and the ensuing development of large billows.