Synthesis of a CFD benchmarking exercise for a T-junction with wall

This article reports the CFD benchmark to validate different turbulent modelling approaches for transient heat transfer in the context of high-cycle thermal fatigue due to mixing of hot and cold flow in a T-junction including the wall. This validation exercise has been carried out within the MOTHER project. In the framework of the project, new experiments were performed with a novel measurement sensor allowing the measurements of the fluctuating wall temperature inside the solid in the mixing region between hot and cold water after a T-junction. The tests were performed for two different Reynolds numbers 40,000 and 60,000 and for two different T-junction geometries; a sharp corner and a round corner. The CFD validation study has been performed using five different CFD softwares, namely STAR-CCM+, Code_Saturne, LESOCC2, Fluent and OpenFOAM. In addition, seven different turbulence models i.e. wall resolved LES, wall function LES, VLES, DES, PRNS, URANS, RANS and AHFM (RANS), were used to perform the CFD computations. The validation exercise has shown that LES shows the best agreement with the experimental data followed by hybrid (LES/RANS), URANS and RANS models, respectively. The velocity and the thermal fields in the fluid region are correctly predicted by the proper use of the LES modelling. Whereas, the accurate prediction of the thermal field in the solid requires very long sampling time to achieve statistically converged solution, which of course requires an enormous computational power. Therefore, the statistical convergence of the thermal field in the solid has been found to be one bottleneck in order to accurately predict the temperature fluctuations in the wall and the transient heat transfer. However, measuring the small amplitude temperature fluctuations is also associated with an uncertainty so the disagreement between CFD and measurements (of the order of 10%) can also be attributed, in part, to uncertainties in the measurements.