Effects of rotation on turbulent mixing across a density interface

The effect of rotation on mixing across a density interface is studied experimentally in a two-layer stratified fluid. Mixing is caused by turbulence produced in one of the layers by an oscillating grid. The flow depends on the Richardson number Ri = g ′ l / u 2 and the Rossby number Ro = u /2Ω l . The most important result is the observed decrease of the entrainment rate E in the presence of rotation, when compared with non-rotating experiments. In a certain range of the two parameters, a general entrainment law in the form E = 0.5 RoRi −1 is established, whereas the entrainment law in non-rotating conditions is E = 1.6 Ri-3/2 . Additional information concerning the dynamics of the interface in rotating conditions is provided by interface displacement spectra, showing that rotation favours low-frequency oscillations of the interface, whereas high-frequency oscillations are not modified by rotation. Finally, the role of inertial waves is discussed on the basis of velocity measurements in the non-stirred layer.