LES and URANS predictions of thermal load in piping systems; T-Junction

The present numerical study focuses on the predictions of thermal mixing in a T-junction using two types of approaches; the Large Eddy Simulation (LES) and the Unsteady RANS technique. The numerical predictions are compared to the experimental reference data of Westin et al. (2008). Beforehand, the LES using the commercial code Star-CD are across validated with the open source Code-Saturne in a simple academic channel flow case at Re=395. For this case, both codes predictions are found in a satisfactory agreement with the DNS data which provides sufficient evidence, from a numerical dissipation related issues point of view, that any of these codes can be used for the LES runs of the more complex T-Junction test case. For the later, in agreement with previous findings reported in the open literature the LES approach is found capable to mimic correctly the flow behavior and to provide valuable instantaneous data needed for the thermal stress fatigue analysis for instance. The URANS technique on the other hand, even with an advanced non-linear eddy-viscosity model, is not only incapable of predicting correctly the mean variables, but also largely dumping the flow turbulence.