New design reduces the ship’s drag

A research team from Chalmers University of Technology, Sweden, has demonstrated a unique method that can reduce ships’ aerodynamic drag by 7.5%.

The method focuses on the steady-flow Coanda effect – the tendency of a liquid – like water on the back of a spoon – to flow along a convex surface rather than splashing away from it.

In shipping, one of the main sources of drag is the square back of the ship’s superstructure, and the new method developed by the Chalmers researchers induces the Coanda effect around this area.

“By creating a design with convex edges on the ship’s superstructure and allowing highly compressed air to flow through nozzle slots, the Coanda effect allows air pressure to equalize at the ship’s hull. This, in turn, significantly reduces drag and makes the ship more energy efficient,” says Kewei Xu, postdoctoral researcher at Chalmers.

Inspired by aerodynamic technologies from aviation, the process is considered particularly relevant for future wind navigation. Previously, aerodynamic effects were not considered important compared to the resistance of a ship in the water.

Researchers claim it paves the way for large cargo ships powered by sails, as wind-powered ships are more affected by drag than engine-powered ones.

The technology could also enable safer helicopter take-offs and landings on ships. Turbulence is usually created when air rushes down from the ship’s superstructure and destabilizes the helicopter. Since pilots have to land or take off at a very precise location on the ship, this involves great risks. Fences or an adapted form are currently used on the ship to mitigate risks, but they are not very effective, the Chalmers researchers say. The new process dampens the turbulence as it affects the wind blowing down behind the structure.

The Coanda effect is named after the Romanian inventor Henri Coanda, who was the first to recognize the practical application of the phenomenon in aircraft construction around 1910. Today the effect is used in jet aircraft, where aerodynamic lift is increased as the jet stream “sticks” to the wing. The Coanda effect affects air and liquid flow in many different contexts, such as: B. Air conditioners.

The method, which can be used on both existing and newly designed ships, is described in an article published in Physics of Fluids.