An approach taking into account the contribution of the processes of the structural relaxation of nematic liquid crystals in an ultrasonic field to the mechanism of the generation of stationary acoustic flows in a thin layer of a material at the binary effect in the megahertz range has experimentally been carried out. A new relaxation model has been checked on the results of the measurements of the flow speed in a flat capillary with homeotropic boundary conditions under the simultaneous effect of the coherent compression and shift waves on nematic liquid crystals. It assumes the existence of two independent acoustic mechanisms of its generation: convective and relaxation. It has been shown that, in this frequency range, a description of the phenomenon adequate to the experimental data can be obtained only within an approach that takes into account both convective and nonlinear relaxation stresses in the medium. The parameters determining the spheres of influence of different mechanisms have been revealed.