Friction factors for idealised 2D stratified channel flow

Friction factors and associated friction velocities are important flow characteristics. Analytical expressions of wall and interface friction properties are derived for idealised three layered and two layered pressure driven stratified flow in a two-dimensional channel under the assumption of fully developed laminar viscous flow. Channel inclination is accounted for as well. The influence of flow and geometrical channel parameters is then concretely assessed for water/air and oil/air interfaces due to their potential relevance to two phase flows occurring in the human airways.