Effects of turbulent Schmidt number on CFD simulation of $$45^\circ $$ inclined negatively buoyant jets

Abstract

Employing inclined negatively buoyant jets is one of the most advantageous means to discharge brine or waste in coastal environments. However, numerical prediction of mixing parameters for this kind of flow is still a challenge. In this investigation, CFD simulations of $$45^\circ $$ inclined dense jets were conducted using realizable k– $$\epsilon $$ model with buoyancy corrections and different values of turbulent Schmidt number ( $$Sc_t$$ ) within two approaches in a finite volume model (Open FOAM). In the first approach, seven scenarios with different values of $$Sc_t$$ were simulated. In the second one, a Regional Turbulent Schmidt Number (RTSN) configuration was introduced based on different behaviors of the flow in jet-like, plume-like, and inner/outer regions. Regarding the first approach, results showed that changing the turbulent Schmidt number has significant consequences for mixing and geometrical parameters. Reducing $$Sc_t$$ from 1.0 to 0.4 led to more than $$\sim 60\%$$ and $$\sim 40\%$$ improvements in dilution ratio at return point and centerline peak, respectively. Using RTSN approach successfully improved the mixing parameters along with keeping nearly unchanged the accuracy of geometrical parameters. That was the case, specifically at return point in comparison with using any other constant $$Sc_t$$ for the whole domain (first approach). This local (regional) change in turbulent Schmidt number compensates for flaws of Boussinesq approximation in the linear two-equation turbulence modeling of inclined negatively buoyant jets. Comparing to the previous LES results, the RTSN approach combined with the realizable k– $$\epsilon $$ model stands as an economically superior solution employing much lower grid numbers.