Wave-number selection and phase solitons in spatially forced temporal mixing layers

The temporally growing shear layer produced by tilting a tube filled with two immiscible fluids of different density is spatially forced via modulations of one of the lateral boundaries. The competition between the forcing wave number kf and the intrinsic wave number kn leads to a mode diagram that is compatible with corresponding observations of spatial mixing layers. As the detuning is gradually increased, the interface displays stationary phase solitons that are indicative of the existence of incommensurate states.