Numerical Study on Wind-Driven Thin Water Film Runback on an Airfoil

Abstract

A method that combines the Eulerian multiphase flow (EMF) model with the Eulerian wall film (EWF) model is proposed to study the transportation of a wind-driven thin film caused by the impingement of water droplets. The external flow of air and droplets is simulated using the EMF model, while the wind-driven film is simulated with the EWF model. The effects of convection, shear stress, gravity, surface tension, and contact angle on the runback film flow are examined. The results show that shear stress from the air and capillary force due to the contact angle at the contact line are the two dominant influences on transportation, with the former acting as the driving force, while the capillary force at the contact line holds back the film and can cause a drastic increase in thickness at the contact line. With increased contact angle, the coverage of the film retracts, but film thickness upstream is not affected. A model for the film velocity containing the effects of shear stress and contact angle was proposed based on the analysis, which can be simplified to Newton’s shear law when the incoming velocity is large or the contact angle is small.