Numerical Simulation Of Stratified Flows With Combined Temperature And Salinity On Unstructured Grids

Stratified flows are often induced by single component (e.g. temperature, active scalars) or multi-components in natural water body. Multi-components caused complicated flow characteristics of stratified flows due to the difference of their own diffusion and component's contribution to water density. Numerical simulation is one of effective methods to study stratified flows, especially for complex conditions where experiments and field investigations are hard to conduct or cannot be collaboratively studied. However, some difficulties exist in current researches. Numerical methods currently used cannot fit the complex geometry well because of the utility of rectangle and orthogonal curvilinear grids. And current researches mainly focus on stratified flows with single component, neglecting the coupling effects of multi-components. In the paper, stratified flows with combined temperature and salinity are investigated on unstructured computational grids. First, unstructured, collocated finite volume method for Navier-Stokes equations is developed under the philosophy of generality. The pressure-velocity coupling is treated using SIMPLE-like algorithm and explicit correction step technique is applied to speed the convergence rate. The hybrid quadrilateral/triangular grids adopted can fit arbitrary geometry. Test cases show that even on distorted grids, results with same-order accuracy can be obtained using present unstructured model. Also QUICK scheme that has a good performance in simulating mass transport in fluid flows, is extended to present unstructured model. And then, numerical simulation of double diffusive in a square cavity with opposing temperature and concentration gradients is executed. Effects of Rayleigh number, Lewis number and buoyant ratio on flow structure and distribution temperature and concentration are analyzed at large. Next, aiming at the state of the art in engineering turbulence models, one extended explicit algebraic Reynolds stress model to simulate anisotropic buoyant turbulent flows. Validation was done using experimental and other numerical results of turbulent thermal mixing in T-junction flows. Finally, the proposed anisotropic buoyant turbulence model is applied to study turbulent density flows with combined temperature and salinity discharging into a tank with a slope bottom. Three kinds of inflows with different combination of temperature and salinity are studied. Results show that difference of diffusion between temperature and salinity have little effect on mean flow fields. But significant effects will arise when components are distinct in contribution to water density.