Page 17: of Maritime Reporter Magazine (February 2026)

Physics of the Jet–Air–Hull Interaction CFD Modeling: VOF multiphase modeling, and k–? SST

The Coanda effect describes the ten- Multiphase Flow Insights turbulence models were used to study jet dency of a ? uid jet to adhere to a nearby Proof of concepts was conducted us- adhesion, air entrainment, air-sheet for- straight or convex curved surface due ing high-? delity CFD simulations with mation, and pressure-? eld characteristics.

to entrainment-induced pressure drop.

When the pressure difference becomes suf? ciently large, the jet “bends” to- ward and follows the contour of the adjacent surface.

The novel insight in this system is that the same mechanism can be exploited not only in air but also across the air-water interface and underwater, enabling en- trained air to form a lubricating air sheet along a submerged hull surface.

A small nozzle angle, typically 1–5 degrees, ensures smooth jet adhesion and momentum preservation. As the jet ? ows along the hull surface, entrain- ment reduces static pressure, forming a continuous low-pressure line that draws atmospheric air toward the hull.

Before entering the water, the free jet entrains a volume of air due to the

Figure 3: CFD analysis for the generated air sheet represented by contours of volume fractions, shear layer. When crossing the water 0 being water and 1 being 100% air (reproduced from patent, US 12,280,854 B2, System and surface, the jet penetrates and carries

Method for Reducing Drag on the Hull of a Vessel, 2024).

air downward, forming a submerged vacuum air sheet.

The high-speed entrained air on the

Coanda effect ? ow eventually slows down enough such that the vessel’s speed water can dislodge it from the Coanda ? ow and push the entrained air aftward. Any air aft of this Coanda ? ow is under a lower pres- sure compared the pressure in the ? ow domain without the presence of the jets.

External water is in contact with the outer side of the vacuum air sheet, while air entrainment continuously feeds it. It is possible that the external water ? ow on the outer side of the vacuum air sheet acts as a pressure barrier due to the relative motion of the air sheet to the external wa- ter, at vessel speed. The vacuum air sheet has a pressure gradient, being a lower vacuum pressure at the forward end and a higher pressure at the aft end. Regardless of the ship and hull design, the developed vacuum air sheet adheres to the hull and follows the hull form contours. This con- tributes to the ease of retro? tting of the system for all existing hull shapes. www.marinelink.com 17

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