Wärtsilä’s pre-swirl stator boosts propulsion efficiency by 10%

Wärtsilä has launched an energy-saving device that has demonstrated fuel savings of up to 10%.

The EnergoFlow is a pre-swirl stator that reduces power losses in the propeller’s slipstream by optimising flow. It works by guiding one side of the stern flow in the opposite direction of the propeller rotation.

A typical ship’s hull will result in water leaving its aft flows at a slight upward angle as it moves towards the propeller. While this is ideal, on the opposite side of the propeller the water and blade move upwards, reducing the propeller’s ability to push against water. This leads to a weakened propulsion power.

To counteract this effect, the pre-swirl stator was developed. This consists of multiple fins (typically three) attached to the ship’s hull to drive a downward wake and get a better angle.

Following an EU-research funded study from 2011-2015 that developed a pre-swirl stator to save power by 7%, Wärtsilä developed an even better pre-swirl stator using multiple curved stator fins attached to the ship’s hull. The fins work by minimising the viscous resistance and optimise the flow into the propeller to prevent power losses. The fins have rings connecting them at their tips, which decreases the peak stress of each fin.

The solution, named EnergoFlow, accurately directs the pre-swirl flow. It lowers resistance, resulting in easier propulsion for less power. This contributes to significant fuel savings.

Tamara de Gruyter, Vice President, Propulsion System Services explains “As the result of increased propulsive efficiency and subsequent energy savings, Wärtsilä EnergoFlow reduces the emissions of ships. Investments in energy-efficient solutions ensure cost savings, compliance with maritime regulations and reduced environmental footprint.”

Computational Fluid Dynamics modelling is carried out on each ship’s operating profile to create a strategy for installing the Wartsila EnergoFlow. The stator is custom-designed for each case, with some variations in the shape of fins and even the number of fins.

According to Wartsila, fuel savings are highest on bulk carriers, tankers, and other full form vessels. Within one to two years of operation the savings generated by EnergoFlow are paid back.