Browsing by Subject "Density interface"

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Erosion of a sharp density interface by homogeneous isotropic turbulence
(2019-05) Lagade, Joel Albano; Johnson, Blair Anne
Desalination, commonly used for potable water production, generates brines that are ultimately released back into the environment. Desalination brines discharged into coastal regions with weak currents and mild bathymetry, such as the Gulf of Mexico, do not necessarily mix with surrounding natural waters and remain stably stratified (Hodges et al., 2011). Because dense immobile saline layers from these discharges can cause hypoxia and threaten local ecosystems, we are conducting an experimental study to investigate the effect of turbulence on a sharp density interface to identify mechanisms of turbulence that promote and/or inhibit interfacial erosion. There remains a gap in the literature regarding the interaction of mean shear free homogeneous isotropic turbulence with a sharp density interface, a critical component in understanding dynamics across a stably stratified system. To address this fundamental question, we use randomly actuated synthetic jet arrays (RASJA - Variano & Cowen (2008)) to generate homogeneous isotropic turbulence, absent mean shear, above a dense fluid layer. The Richardson number is varied to ascertain the thresholds at which the density interface erodes and mixing between the stratified layers occurs. As in Johnson & Cowen (2018), who characterized the mean shear free turbulent boundary layer at solid and sediment beds, particle image velocimetry is used to complete a statistical analysis of the turbulent flow field at and above density interface. Simultaneous laser induced fluorescence measurements are obtained to capture erosion, sharpening, and mixing. Statistical metrics of the turbulence are coupled with the evolution of concentration profiles and mixing, which is determined by measuring temporally resolved isopycnal displacements. In the current work, we provide the first experimental data to test quantifying entrainment across stratified fluids as described and applied in direct numerical simulation studies by Zhou et al. (2017). By examining the interplay between mean shear free homogeneous isotropic turbulence and a sharp density gradient, we aim to deduce under what environmental conditions it is sustainable to discharge brine into relatively quiescent flows, considering key factors such as ambient turbulence and relative salinity variance between the brine and surrounding waters.