Steady-state RANS-simulations of the mixing in a T-junction

Steady-state CFD post-test calculations of T-junction mixing experiments are presented. The adiabatic experiments were carried out on a horizontally oriented T-junction with a straight main branch and a side branch coming in under an angle of 90°. The inner diameter of the pipes was 51 mm. Two streams of water with a different concentration of dissolved ions were mixed. The transport scalar distributions were measured by wire-mesh sensors sensible to the electrical conductivity, which is proportional to the concentration. Calculations were performed with ANSYS-CFX-10 using the k–ɛ, SST and BLS Reynolds stresses models. It was found that both turbulent mixing and turbulent momentum transport downstream of the side-branch connection are underestimated by all three models. In the consequence, calculated transport scalar and velocity profiles are less uniform than the measured ones, especially at higher distances. Concerning the mixing, a decrease of the turbulent Schmidt number improves the agreement, although some qualitative discrepancies remain evident. Better results were obtained by increasing of the model coefficient Cμ in the k–ɛ model, leading to an improvement of both concentration and velocity profiles.