Computational fluid dynamics (CFD) simulations are conducted to explore flow inside a channel with staggered semi-circular ribs attached to both the inner and outer annular walls. Large eddy simulation (LES) with the wall-adapting local eddy-viscosity (WALE) sub-grid scale (SGS) model is used to simulate turbulent flow in the computational domain. The flow channel is modeled on the test section of a simplified helical coil steam generator (HCSG) design. Owing to their compactness and higher heat transfer coefficient in comparison to straight tube steam generators, HCSGs are employed in recent designs of advanced light water reactors in the nuclear industry. A Reynolds number of 13,900 is considered based on the mean inlet velocity, channel height, and water properties. Results from LES are compared with both an unsteady Reynolds-Averaged Navier-Stokes (URANS) simulation and experimental data acquired from the particle image velocimetry (PIV) method. Flow features observed inside the channel are presented by visualizing contours of velocities, vorticity, and Reynolds stresses on a monitoring plane. Time-averaged profiles of velocities and Reynolds stresses at five monitoring lines are also presented to validate the flow field resolved by LES with PIV. Additionally, vortical structures of the flow are captured using the Q-criterion. This study aims at providing flow characteristics of a specifically designed flow channel and acquiring the scalability of the numerical experiment. (C) 2018 Elsevier Ltd. All rights reserved.