Hybrid momentum theory for air drag reduction of flat-plate boundary layer under air film

A hybrid momentum theory of flat-plate boundary layer was proposed, to elucidate drag reduction on a van body surface under air film. The air mass and momentum before and after the outside air mixed with film air were compared, which may lead to the change of viscous force. A mathematical model for flat-plate boundary layer under air film was established based on the law of mass and momentum conservation, with selecting a unit of laminar boundary layer as analysis object and simultaneous solution of the momentum integral equation and the velocity distribution equation. The mass of air flow, momentum flux, loss of momentum, boundary layer thickness and surface viscous force were discussed to take a comparative analysis of flat boundary layer’s status change with and without an air film.