Simulation of turbulent and thermal mixing in T-junctions using URANS and scale-resolving turbulence models in ANSYS CFX

Being of importance for turbulent and thermal mixing and consequently for thermal striping and thermal fatigue problems in nuclear power plants, the turbulent isothermal and thermal mixing phenomena have been investigated in two different testcase scenarios. First testcase scenario as proposed by ETHZ(Zboray et al., 2007) comprises of turbulent mixing of two water streams of equal temperature in a T-junction of 50 mm pipes in the horizontal plane and thereby excluding any buoyancy effects. The second testcase is based on the Vattenfall test facility in the Alvkarleby laboratory and has been proposed by Westin (2007) where water of 15 K temperature difference mixes in a T-junction in vertical plane, provoking thermal striping phenomena. ANSYS CFX 11.0 with Reynolds averaging based (U)RANS turbulence models (SST and BSL RSM) as well as with scale-resolving SAS-SST turbulence model has been applied to both test cases. CFD results have been compared to wire-mesh sensor, LDV and thermocouple measurements. While the turbulent mixing in the ETHZ testcase could be reproduced in good quantitative agreement with data, the results of the LES-like simulations were not yet fully satisfying in terms of the obtained accuracy in comparison to the detailed measurement data, also the transient thermal striping phenomena and large-scale turbulence structure development was well reproduced in the simulations. (C) 2009 Elsevier B.V. All rights reserved.