Experimental study on gravity currents with internal stratification in semicircular channels

Abstract

We present an experimental study of gravity currents (GCs) with internal stratification in a semicircular channel in the inertial–buoyancy and Boussinesq regime. Forty tests were performed with a denser volume of fluid (brine advancing in a fresh water ambient fluid) in lock-release. The lock contains an internal stratification, with a layer of density ρL overlain by a layer of density ρU, where ρa<ρU<ρL and ρa is the density of the ambient fluid. The experiments cover both a full depth and a partial depth configurations. The measurements consist of marking the front position of the currents as a function of the time from release, t. Two lateral video-cameras were used to detect the flow profile. Also local instantaneous density and velocity profiles data were collected in a fixed section downstream of the gate, in order to give further details and a better description of the physical phenomenon. The data of front speed and current thickness were compared to a theoretical model (Zemach and Ungarish, 2021) based on (i) a Boussinesq flow; (ii) large Reynolds number; (iii) current advancing in shallow water conditions; and (iv) negligible ambient fluid dynamics. The system of equations and boundary conditions allow the prediction of the motion of the GC, in particular the position and speed of the nose xNt and uNt. The agreement of theory and experiments is fairly good, especially for the full depth configuration. The partial depth configuration experiments are less accurately reproduced by the theory, and require a correction coefficient of the Froude number at the front, that accounts for the deviations of the realistic system from the free-slip and sharp non-entraining interface in the control volume about the head.