  In this paper, the novel experimental data reported by Qin et al. [1] are
used to assess the predictive capability of the Realizable k-epsilon (RKE)
model and Reynolds stress transport (RST) model for buoyant jets and understand
the reasons for discrepancies. In particular, we present the comparison between
simulation results of a turbulent buoyant jet flow in the self-similar region
with high-resolution experimental data obtained for a jet injected from a 2 mm
nozzle into a 300x300x300 $mm^3$ tank, with nominal Reynolds number equal to
10,000. Results show that streamwise velocity profiles predicted by the RST
model had good agreement with experimental data, while the larger spreading
rate was predicted by the RKE model. For turbulent statistics, turbulent
kinetic energy witnessed a discrepancy in the center region, with shear stress
well predicted for both models. Comparison of the turbulent kinetic energy
production term with experimental data revealed reasons for the discrepancy and
also showed that the gradient of the streamwise velocity in the crosswise
direction contributes the most to the turbulent kinetic energy production.
Investigation of model coefficients of the turbulent dissipation equation for
the RKE model has revealed that $C_{\varepsilon2}$ is critical in model
accuracy.
