Numerical investigation of two plane parallel turbulent buoyant jets: Effects of jet spacing and Richardson number on flow interaction and thermal transport

Abstract

This study presents a numerical investigation of two plane parallel turbulent buoyant jets (TPBJ) to examine the combined effects of jet spacing and buoyancy on flow interaction and thermal transport. Steady-state simulations are conducted by solving the Reynolds-averaged Navier–Stokes equations using the standard $k-ϵ$ turbulence model with the Boussinesq approximation. The analysis considers jet spacing ratios ($s/d=3$ to 11), where $s$ is the centre-to-centre jet spacing and $d$ is the nozzle width, and Richardson numbers ($Ri=0$ to 1/2) to represent varying buoyancy levels. Results indicate that narrower spacing enhances jet interaction, strengthens entrainment, and leads to earlier merging, while wider spacing delays interaction and weakens vertical momentum. Buoyancy significantly alters the flow structure by accelerating jet convergence, increasing centreline velocity, and confining both velocity and thermal plumes. Three characteristic axial locations, namely, the merging point (MP), combined point (CP), and maximum velocity point (MVP), are identified and correlated with $s/d$ and $Ri$. In the far field, the lateral growth of velocity and thermal widths becomes approximately linear, though spreading rates decrease with increasing buoyancy. The centreline velocity and temperature exhibit decay consistent with power-law behaviour, influenced by buoyancy strength. Empirical correlations are proposed to predict the axial positions of MP, CP, and MVP with high accuracy. These correlations can be directly applied in engineering design and environmental applications, including the optimization of jet-based cooling configurations, ventilation layouts, and buoyant discharge systems, where a rapid yet reliable estimation of jet interaction characteristics is essential. Compared to isothermal jets ($Ri=0$), buoyant jets show enhanced centreline velocities, stronger recirculation, and reduced lateral dispersion. These findings provide new insights into the coupled momentum and thermal dynamics of TPBJ systems and offer predictive tools for applications in thermal management and environmental jet discharge.