assessing rans-based turbulence models for mixed convection: predictions of flow stability and mixing length

This study offers a comparative assessment of multiple turbulence models for predicting mixed convection within an axisymmetric exhaust column, where a hot jet rises through a cooler ambient region. the simulations employ several rans-based models—realizable k–ε, k–ω sst, and the reynolds stress model (rsm)—to capture velocity profiles, temperature distribution, and turbulence characteristics in a buoyancy-driven flow. a structured mesh, refined near the walls, ensures accurate resolution of boundary-layer phenomena. quantitatively, the realizable k–ε model predicts significantly lower inlet and outlet mass flow rates (approximately 11 and 9 kg/s, respectively) compared to the rsm and k–ω sst results (both exceeding 30 kg/s). the realizable k–ε solution also forecasts an outlet velocity below 1 m/s, producing reversed flow regions and undervaluing outlet temperature (around 300 k). in contrast, the rsm and *k–ω* sst models consistently maintain strong upward flow with outlet velocities around 2–2.3 m/s and higher outlet temperatures (approximately 325 k), indicating minimal recirculation. these findings underscore the significant impact of turbulence model choice on capturing reversed flow behavior and accurately predicting mass flow rates, temperatures, and velocity fields in mixed convection applications.