Numerical simulation of turbulent flow in an eccentric channel

The aim of this work is to perform a numerical simulation of the turbulent flow in an eccentric channel for a Reynolds number Re-Dh = 7300. The Reynolds number is based on the bulk velocity, U-Bulk, the hydraulic-diameter, D-h, and the kinematic viscosity, nu. To achieve this goal, a hybrid RANS/LES turbulence model called DES-SST is used. In this formulation, special functions are computed to convert the model from RANS close to the walls to LES in more remote regions. Besides the Reynolds number, the main dimensionless parameter related to the geometry involves the narrow gap between the outer and inner walls of the pipes and their diameters, D and d, respectively. These geometric parameters are related to the eccentricity, e, and the d/D ratio. Both of these parameters were kept constant at 0.80 and 0.50, respectively, throughout the work, as the channel's length, L = 1500 mm. The numerical results are compared with experimental outcomes for a water channel with the same Reynolds number using Ply measurements. The hybrid scheme was able to capture the onset of gap instability, short after the channel's inlet. Furthermore, the mass flow distribution along the channel and the flow velocity patterns were also successfully predicted by the numerical code. The Strouhal number was found to be in fair agreement with the experimental result. The large-scale structures were found to spread over the whole cross-section. The main frequency produced by the oscillatory motion in the tight gap was seen to be twice as high as that found in the lateral subchannel. (C) 2020 Elsevier Masson SAS. All rights reserved.