The Effect of Buoyancy on the Turbulence Structure of Vertical Round Jets

The paper presents an application of the algebraic stress modeling (ASM) technique to the prediction of the flow in a turbulent round buoyant jet. In the ASM approach, algebraic formulas are obtained for the Reynolds stresses, u_iu_j, and for the components of the turbulent heat flux, tu_i. In the model used here, transport equations are solved for the turbulence kinetic energy, k, its dissipation, ε, and the mean square temperature fluctuations, g. The study shows that buoyancy increases the rate of dissipation of g above the values indicated by previous recommendations for the modeling of that quantity. As a possible explanation for this result it is suggested that buoyancy introduces anisotropy in the fluctuations at the dissipation scale. The study shows that the contribution from the secondary components of the strain tensor to the production of k is non-negligible. In addition, between 12 and 17 percent of the longitudinal enthalpy flux is contributed by the turbulent fluctuations. Finally, it is observed that the modeling of buoyant flows still presents uncertainties and that additional work is necessary to properly account for the effect of buoyancy on the production of ε and the dissipation of g.