An axisymmetric non-hydrostatic model for double-diffusive water systems

Abstract

The three-dimensional (3-D) modelling of water systems involving double-diffusive processes is challenging due to the large computation times required to solve the flow and transport of constituents. In systems that approach axisymmetry around a central location, computation times can be reduced by applying a quasi 3-D axisymmetric model setup. This article applies the Navier-Stokes equations described in cylindrical coordinates, and integrates them to guarantee mass and 5 momentum conservation. The discretized equations are presented in a way that a Cartesian finite volume model can be easily extended to this quasi 3-D framework, which is demonstrated by the implementation into a non-hydrostatic free-surface flow model. This model employs temperature and salinity dependent densities, molecular diffusivities, and kinematic viscosity. Four qualitative case studies demonstrate a good behaviour with respect to expected density and diffusivity driven 10 flow and stratification in shallow water bodies. A fifth case study involves a new validation method that quantifies the radial expansion of a dense water layer developing from a central inflow at the bottom of a shallow water body.

Skin Effect of Fresh Water Measured Using Distributed Temperature Sensing

“…Existence of a colder layer of water on top of warm water creates instability. The cold layer will periodically mix with the warmer water below through finger-like structures [36]. The creation of a colder layer of water near the water surface can be approached from the energy-balance point of view.…”