Numerical and experimental investigation of inclined negatively buoyant jets in quiescent water using a RANS-based InterMixingFoam solver

This study presents a combined numerical–experimental investigation of inclined negatively buoyant jets discharged into a quiescent ambient. The investigation employs the InterMixingFoam solver in OpenFOAM with three RANS turbulence models (k-ε, RNG k-ε, and realizable k-ε). Although dense jets have been extensively studied, limited attention has been given to multiphase solvers that simultaneously resolve free-surface dynamics and scalar mixing. This is particularly critical for coastal brine disposal, where buoyancy-driven jet behavior governs near-field dilution. Laboratory experiments provided centerline trajectories and geometric jet characteristics for discharge angles of 30°, 45°, and 60°, while numerical simulations yielded scalar concentration fields for analyzing dilution and centerline concentration decay. Results indicate that InterMixingFoam reliably reproduces key hydrodynamic features, including jet rise, terminal height, and return point, with the standard k–ε and RNG k–ε models showing closest agreement with experiments across all angles. Power-law analysis of centerline concentration demonstrated consistent decay, with both models yielding stable exponents and high coefficients of determination. The realizable k-ε closure moderately over-predicted geometric centerline metrics and produced weaker decay rates, indicating reduced turbulent mixing. Although simulations were limited to single-port nozzles and quiescent ambient conditions, InterMixingFoam's validated ability to resolve free-surface dynamics enables future extensions to more realistic scenarios, such as wave–jet interactions, background currents, stratification, and multiport diffuser configurations. Overall, the findings confirm the applicability of InterMixingFoam with k-ε-family models as a reliable framework for predicting near-field behavior of inclined dense jets.