SYMMETRY BREAKING AND TURBULENCE IN OSCILLATORY FLOW THROUGH A HEXAGONAL SPHERE PACK

The appearance of turbulence in oscillatory flow through a hexagonal sphere pack was investigated by means of direct numerical simulation. The Reynolds numbers lie between 26.9 and 297 and the Womersley number is 31.62. We characterised the flow state based on instantaneous velocity fields and the time series of the superficial velocity. The velocity fields were decomposed into symmetric and antisymmetric components with respect to the symmetries of the sphere pack. Based on the temporal evolution of the kinetic energy of the antisymmetric components, it is possible to distinguish between laminar, transitional and turbulent flow. Finally, the velocity fields were decomposed with respect to the average over the realisations that can be obtained by applying the symmetries of the hexagonal sphere pack. For the turbulent flow case, a significant scale separation between the average and fluctuating velocity fields is observed.