Gravity currents in a linearly stratified ambient fluid created by lock release and influx in semi-circular and rectangular channels

Abstract

We present an experimental investigation, supported by a theoretical model, of the motion of lock-release, constant inflow, and time varying inflow gravity currents (GCs) into a linearly stratified ambient fluid at large Reynolds number. The aim is the experimental validation of a simple model able to predict the slumping phase front speed and the asymptotic self-similar front speed for rectangular and circular cross section channels. The first investigated system is of Boussinesq type with the dense current (salt water dyed with aniline) released in a circular channel of 19 cm diameter and 400 cm long (605 cm in the inflow experiments), half-filled of linearly stratified ambient fluid (salt water with varying salt concentration). The second system has the same components but with a channel of rectangular cross section of 14 cm width, 11 cm ambient fluid depth, and 504 cm length. The density stratification of the ambient fluid was obtained with a computer controlled set of pumps and of mixing tanks. For the experiments with inflow, a multi-pipes drainage system was set at the opposite end with respect to the inflow section, computer controlled to avoid the selective withdrawal. The numerous experiments (28 for circular cross section, lock release; 26 for circular and 14 for rectangular cross section, constant inflow (fluid volume ∝tα, with α = 1); 6 for circular cross section, linearly increasing inflow (α = 2)), with several combination of the stratification parameter (0 < S < 1) confirm the theory within ≈30% (≈40% for a single series of experiments), which is considered a good result in view of the various underlying simplifications and approximations. The results on the front speed of the GCs are discussed in the presence of the internal waves, which have a celerity given by a theoretical and experimentally tested model for the rectangular but not for the circular cross section. The theoretical analysis of internal waves in circular cross sections has been extended and experimentally validated.

Impact of Density Gradients on the Secondary Flow Structure of a River Confluence

“…The gradient forces a front of the denser river to extend laterally along the bed, which due to the incompressibility constraint (Horna‐Munoz et al., 2020), also causes a front of the lighter river to flow above in the opposite direction. The resulting cross‐flow is similar to the dense and light fronts of a lock‐exchange in the initial moments after its release (Cantero et al., 2007; Longo et al., 2015, 2016; Rottman & Simpson, 1983), and has been modeled in a geometry similar to that of a parallel confluence by White and Helfrich (2013). However, where the fronts are sufficiently opposed by the adjacent tributary, the dense front is deflected above itself and the light front downwards.…”

Experimental study on radial gravity currents flowing in a vegetated channel

“…The order of the polynomial is automatically chosen to minimize the root-mean-square deviation between the grid knots in laboratory coordinates and the reconstructed values starting from the pixels in the image. The conversion polynomials allow us to compensate for defects in the optics and for the position of the camera (Longo et al 2015(Longo et al , 2016, and are used to transform the pixels corresponding to the instantaneous profile of the current into laboratory coordinates.…”

“…The great interest in this broad natural phenomenon, and the enormous variety of configurations in the environment and industry, has stimulated a rich line of theoretical and experimental research, with advanced numerical techniques and sophisticated measuring instruments. The simplest configuration, with a horizontal bottom, is perhaps the one most intensively investigated, starting with Benjamin's pioneering publication (Benjamin 1968) with numerous extensions to a general cross-section (Ungarish 2018), and with stratification of the ambient fluid (Longo et al 2016).…”

Effect of stratification on the propagation of a cylindrical gravity current

“…Planar release gravity currents in stratified (Maxworthy et al 2002;Ungarish & Huppert 2002;Birman et al 2007b;Longo et al 2016;Chiapponi et al 2018;Lam et al 2018b;la Forgia et al 2020;Ottolenghi et al 2020;Dai et al 2021;Zahtila et al 2024), and unstratified ambients (Rottman & Simpson 1983;Shin, Dalziel & Linden 2004;La Rocca et al 2008;Dai 2015;Pelmard, Norris & Friedrich 2018;Dai & Huang 2020;De Falco, Adduce & Maggi 2021;Maggi, Adduce & Negretti 2022, 2023aMaggi et al 2023b), as well as cylindrical release gravity currents in unstratified environment have been widely studied experimentally and numerically (Cantero et al 2007a,b;Zgheib, Bonometti & Balachandar 2014, 2015aDai & Huang 2016). However, experimental and numerical studies on stratified gravity currents with the cylindrical release are limited, and therefore we are interested in cylindrical gravity currents propagating into a linearly stratified ambient.…”