A numerical study of buoyant turbulent flows using low-Reynolds number k-e model

Numerical computation has been performed to determine the influence of buoyant eflects on convective flows with the standard k-e and the low-Reynolds number k-s models. The present study was motivated by the need to overcome the shortcoming of the standard k-e model in separating and reattaching flows because of the wall-function approach employed in the model.

The low-Reynolds number k-e model is considered to be an appropriate model for recirculating flows because the model does not employ wall functions. Results of the two different models are compared against the available experimental data and direct numerical simulation (DNS) data. In this work, Kolmogorov velocity, ut=(ve), is introduced instead of shear velocity, ut=Twlp, to avoid the singularity that appears at the separating and reattaching point for both thurbulence models. QUICK differencing scheme is employed for the convective terms. Eddy-diffusivity concept is used in modeling buoyant term. Momentum equation for the velocity field and the energy equation for the temperature field are solved altematively because of the strong coupling that exists between temperature and the velocity fields in a buoyant flow. Turbulent Prandtl number was allowed to vary in the low-Reynolds number k-e model to mimic the experimental data.