A priori testing of large eddy simulation in open channel turbulent flows

An a priori test of large eddy simulation is presented for a turbulent open channel flow subject to stable stratification. This study evaluates the performance of the Smagorinsky and Vreman subgrid scale models across distinctive flow states, including turbulence decay, recovery, and a quasi-stationary state. To explore the characteristics of energy production and subgrid scale dissipation, a spectral cutoff type with various filter sizes is utilized. The results show the limited role of subgrid scale motions in the turbulent kinetic energy production during the turbulence decay phase and when the filter size is reduced. The examination of subgrid-scale dissipation reveals that the location in the vicinity of the shear region around z+≈10 is the source of backscatter energy. It is observed that the wall-normal component of subgrid-scale dissipation initially forms the backscatter energy. Insights from the inspection of subgrid models for predicting subgrid-scale dissipation reveal that the Vreman model tends to outperform another during the different phases of turbulent boundary layer stratification.