Turbulent Characteristics and Anisotropy in Breaking Surge Waves: A Numerical Study

Numerical simulations of breaking weak surge waves produced by the sudden removal of a gate were conducted to investigate the turbulent characteristics generated by different mechanisms in the surge front. We conducted numerical studies using Large Eddy Simulation (LES) over a range of surge Froude numbers from 1.7 to 2.5, and a wide spectrum of tempo-spatial scales down to the Hinze scale was resolved. We established turbulent statistics by means of Favre-averaging where the quantities were weighted by the instantaneous density. Our results demonstrated that the production of turbulent kinetic energy is mainly sourced at the toe, where the shear layer originates. Furthermore, decomposition of production elements illustrated that the shearing action is the principal driver in the entire surge front. Herein, we also conducted intricate anisotropy analyses including establishing characteristic shape maps by pointwise eigendecomposition of Reynolds stress tensors. Near the toe at the core of the mixing layer, prolate structures were evident that are mainly stretched in the streamwise direction. Moving from the mixing layer towards the free surface, however, the structure changes to a combination of prolate and oblate features, where the smallest principal stress is nearly in the spanwise direction. In a snapshot, our results illustrate a clear transition in anisotropy from the recirculating region to the mixing layer.