Numerical CFD study on the frictional drag reduction using air lubrication

Ottosen, Jacob Bjørn Helmers

4. term

Energy Engineering, Master

2022

2022-05-30

73

Dette studie undersøger, om luftsmøring—at injicere luftbobler under et skrog—kan reducere et skibs modstand. Vi bruger flerfaset Large Eddy Simulation (LES) med Volume of Fluid (VOF), som kan beskrive både luft og vand og følge deres grænseflade. De flerfasede simuleringer startes med en turbulent hastighedsprofil fra en enkeltfase (kun vand) model, som valideres mod teori ved at sammenligne det turbulente grænselag med den såkaldte 'law of the wall'. Luftvolumenfraktionen varieres fra 14–50%. Ved 14% luft ses en reduktion i vægskærspænding (friktionen på skroget) på 20–40%. Ved 27–50% luft ses en reduktion på 40–60% i vægskærspændingen i forhold til enkeltfasemodellen. Resultaterne indikerer, at luftsmøring kan give betydelige friktionsreduktioner, afhængigt af mængden af indsprøjtet luft.

This study examines whether air lubrication—injecting air bubbles under a ship’s hull—can reduce drag. We use multi-phase Large Eddy Simulations (LES) with the Volume of Fluid (VOF) method, which model both air and water and track their interface. The multi-phase runs are initialized with a turbulent velocity profile from a single-phase (water-only) model that is validated against theory by checking the turbulent boundary layer with the 'law of the wall'. The air volume fraction is varied from 14–50%. With 14% air, wall shear stress (the friction on the hull) decreases by 20–40%. With 27–50% air, the reduction is 40–60% relative to the single-phase case. These results indicate that air lubrication can substantially cut friction, depending on the injected air fraction.

[This summary has been rewritten with the help of AI based on the project's original abstract]

LES ; VOF ; CFD ; Air lubrication

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