Spectral and modal analysis of the flow in a helical coil steam generator experiment with large eddy simulation

This paper presents an analysis of flow in the shell side of a 24-degree cut helical coil steam generator (HCSG) with large eddy simulation (LES). In the study, the open source, high-order spectral element CFD code Nek5000 was employed for numerical simulation. LES was performed at a Reynolds number of 9000 based on the inlet velocity and tube diameter. Spectral analysis was carried out along the tube bundle to investigate vortex shedding and to reveal shedding frequencies in HCSGs. Wavelet analysis was carried out to determine the time-frequency information of the fluctuating velocities in the domain. Flow was decomposed into modes with proper orthogonal decomposition, which revealed coherent structures in the flow and evolution of coherent structures in time. For the validation of Nek5000 in complex geometries, results from the numerical simulation were compared with experiments conducted at Texas A&M University. Overall, the LES results showed good agreement with experimental data.