Propelling flow simulations forward for waterjet propulsors

High-performance and shallow-water vessels often rely on waterjet propulsors, which move ships by sucking in water from underneath the hull, accelerating it with a pump, and shooting it out the back as a high-speed jet. But the propulsors’ internal flow is far from perfect, causing efficiency decreases that can compromise a vessel’s safety and reliability.

Zhou et al. modeled the water and air flow within a waterjet propulsor to more accurately analyze what happens during marine operations near the surface of the water. They found that ship turning and air ingestion both reduce propulsor performance.

“Many earlier studies focused on simpler conditions, such as straight-ahead motion or pure water flow,” said author Wei Li. “These studies are useful, but they do not fully represent what happens in real marine operations.”

The researchers began by building a three-dimensional computer model of a waterjet propulsor, including its inlet duct, impeller, guide vanes, and nozzle. They then simulated different steering conditions, including straight-ahead motion and left and right turns at various angles. Lastly, they added air to simulate how the system accidentally takes in gas, especially during rough sea conditions.

The simulations showed that steering angles and air intake both decrease the flow rate and thrust of the propulsor. However, air did not spread evenly within the system; it gathered in low-pressure regions, which weakened pressure across the blades and decreased energy transfer to the water.

“Engineers can use the findings to improve the shape of the inlet duct, impeller, or other flow passages to reduce air accumulation and flow distortion,” said Li. “The results may also help guide operating strategies for vessels that often maneuver in complex sea conditions.”

Source: “Investigation on the influence of gas-ingesting inflow on internal flow characteristics of a waterjet propulsor under steering conditions,” by Jinlong Zhou, Wei Li, Yunfei Chen, and Yihan Wang, International Journal of Fluid Engineering (2026). The article can be accessed at https://doi.org/10.1063/5.0306604 .