Study on the Skin-Friction Drag Reduction by Air Injection Using Computational Fluid Dynamics-Based Simulations

Abstract

The skin-friction drag reduction by air injection have been investigated numerically for the turbulent boundary layers first on the underside of flat horizontal surfaces and secondly on the bottom of a real LNG carrier using unstructured finite-volume CFD solver for the Reynolds averaged Navier-Stokes equations. In the present flow computations, two different multi-phase models, such as the volume of fluid (VOF) and the Eulerian multi-phase (EMP), are adopted to investigate their performances in resolving two-phase flow patterns and estimating skin-friction drag reductions. Both VOF and EMP models have similar capability and accuracy in capturing the topology of ventilated cavities, so called ‘air pockets and branches’. However, EMP model is superior to VOF model in predicting quantitatively the percentage of frictional drag reduction by air injection for the cases of both a flat-plate model and an actual ship.