Density current propagation in the presence of regular waves.

Rosaria Ester Musumeci, Laura Maria Stancanelli, Antonio Fichera, Enrico Foti

Thursday 2 july 2015

16:00 - 16:15h at Amazon (level 1)

Themes: (T) Water engineering, (ST) Experimental facilities and instrumentation

Parallel session: 13B. Engineering - River

The propagation of dense saline gravity currents in the presence of a wave field has been investigated experimentally. The aim is to determine the influence of the wave characteristics on a density current forced by the reduced gravity (gā€™). In such a framework the gravity currents were produced through full-depth lock-exchange type of experiments within a wave flume. An optical measurement methodology has been used to detect the geometry and the kinematic characteristics of front propagation, such as: depth, velocity and shape. The kinematic characteristics of the wave motion (i.e. wave height, wave period and vertical velocity profile) have been determined by means of acoustic sensors and of an acoustic doppler velocimeter (ADV). A wide set of experiments has been conducted by considering different reduced gravity values (range of gā€™ = 0.039 ā€“ 0.145) and different wave conditions (i.e. wave height range 1.5-4.3 cm, wave period range 0.7- 1.3 s). The analysis of the data collected during the experiments in the presence of a wave motion indicates that the dynamics of the advancing front of the denser fluid develops with a peculiar oscillatory shape, due to the pulsating force applied by the wave motion, as in earlier works (e.g. Musumeci et al. 2014, IAHR2014). Moreover, it has been observed that the fronts of the gravity currents oscillate with an amplitude and phase that are related with the orbital velocities within a region close to the bed. This phenomenon was also noticed by Robinson et al. (JFM, 2013), who studied the gravity current propagation under a different experimental settings. The experiment results allowed the definition of a trend of the average propagation velocity under different parameters, such as: reduced gravity, Lagrangian mass flux profile and wave height, to be delineated. In general the presence of a wave motion acts as a spurious friction term on the propagation of the density current, although in the presence of long waves higher propagation velocities have been observed when compared with the absence of wave motion.