Experimental study on radial gravity currents flowing in a vegetated channel. (25th February 2022)

• Record Type: Journal Article
• Authors: Petrolo, D.; Ungarish, M.; Chiapponi, L.; Longo, S.
• Is Part Of: Journal of fluid mechanics. Volume 933(2022)
• Publication Date: 2022-02-25
• Subjects: gravity currents -- topological fluid dynamics -- drag reduction; Fluid mechanics -- Periodicals; 532.005
• DOI: 10.1017/jfm.2021.1059
• Languages: English
• ISSNs: 0022-1120

Abstract

Abstract: Abstract : We present an experimental study of gravity currents in a cylindrical geometry, in the presence of vegetation. Forty tests were performed with a brine advancing in a fresh water ambient fluid, in lock release, and with a constant and time-varying flow rate. The tank is a circular sector of angle $30^\circ$ with radius equal to 180 cm. Two different densities of the vegetation were simulated by vertical plastic rods with diameter $D=1.6\ \textrm{cm}$ . We marked the height of the current as a function of radius and time and the position of the front as a function of time. The results indicate a self-similar structure, with lateral profiles that after an initial adjustment collapse to a single curve in scaled variables. The propagation of the front is well described by a power law function of time. The existence of self-similarity on an experimental basis corroborates a simple theoretical model with the following assumptions: (i) the dominant balance is between buoyancy and drag, parameterized by a power law of the current velocity $\sim |u|^{\lambda-1}u$ ; (ii) the current advances in shallow-water conditions; and (iii) ambient-fluid dynamics is negligible. In order to evaluate the value of ${\lambda}$ (the only tuning parameter of the theoretical model), we performed two additional series of measurements. We found that $\lambda$ increased from 1 to 2 while the Reynolds number increased from 100 to approximately $6\times10^3$, and the drag coefficient and the transition from $\lambda=1$ to $\lambda=2$ are quantitatively affected by D, but the structure of the model is not.