Detached eddy simulation of turbulent and thermal mixing in a T-junction

Turbulent thermal mixing is one of the major degradation mechanisms of thermal fatigue, called high cycle thermal fatigue, and a mixing tee has been known as typical component susceptible to high cycle thermal fatigue. From a numerical analysis point of view, accurate prediction of turbulent flow and associated thermal fields in a T-junction is an essential task; that requires computational fluid dynamics (CFD) with advanced turbulence modeling. The detached eddy simulation (DES) model is hybrid turbulence model which combines classical Reynolds Averaged Navier-Stokes (RANS) formulations with elements of large eddy simulation (LES) method. The DES model has a benefit from computational cost point of view, but the studies of its applicability to industrial problems seem to have been conducted relatively insufficiently. Therefore, in this study, transient CFD analysis using the DES model was performed against Vattenfall T-junction test, and the applicability of DES model to turbulent thermal mixing was evaluated by comparing with its experimental data. For the comparison of velocities, the DES results were in good agreement with the experimental data. For the comparison of temperature, the calculated results were generally in good agreement, but at separation region, a large difference of mean temperature was observed. For the locations where the wall temperature variation is large in which the risk of thermal fatigue is expected to be higher, it was seen that the low frequency oscillations are dominant and the energy begins to decrease from ∼4 Hz. In conclusions, it was confirmed that the DES turbulence model has a capability to simulate turbulent thermal mixing phenomenon in a mixing tee and the CFD analysis using that model can provide reliable results for the assessment of the structural integrity of such a piping system.