Tidal Synchronization of Lee Vortices in Geophysical Wakes

Wake vortices in tidally modulated currents past a conical hill in a stratified fluid are investigated using large‐eddy‐simulation. The vortex shedding frequency is altered from its natural steady‐current value leading to synchronization of wake vortices with the tide. The relative frequency ( f * ), defined as the ratio of natural shedding frequency ( f s , c ) in a current without tides to the tidal frequency ( f t ), is varied to expose different regimes of tidal synchronization. When f * increases and approaches 0.25, vortex shedding at the body changes from a classical asymmetric Kármán vortex street. The wake evolves downstream to restore the Kármán vortex‐street asymmetry but the discrete spectral peak, associated with wake vortices, is found to differ from both f t and f s , c , a novel result. The spectral peak occurs at the first subharmonic of the tidal frequency when 0.5 ≤  f * < 1 and at the second subharmonic when 0.25 ≤  f * < 0.5.