Friction at the Interface of Two-Layered Flows

Viscous perturbed velocity field induced by interfacial waves is solved to the first order in terms of wave amplitude for sharply stratified flows described in a curvilinear coordinate system assuming that the external velocity is uniform and constant along the interface. A new type of formula for the interfacial friction coefficient is proposed based on the theoretical result on viscous dissipation in the boundary layer along the interface. The interfacial friction coefficient is supposed to be inversely proportional to the square root of the product of the Reynolds number of a moving layer and the densimetric Froude number to the fifth. The new formula agrees with observed data better than the best empirical law does especially in the range of large Reynolds number.It is found out, however, that the proportional constant may be affected by stability of the two-layered flow system concerned.