Investigating the tip leakage vortex to improve performance of pumps and turbines

Axial flow circulating pumps (AFCPs) are part of marine steam turbine units in large ships. When a vessel is running normally, the sea water pours into the AFCP at a certain flow rate, and the impeller is driven to rotate at a low speed under the impact of the sea water. This provides energy for the vessel’s power system under an unpowered driven condition (UDC). Generally, when the AFCP is operating in an UDC, the flow rate is 10% lower than how it was designed to operate, and the rotational speed is 20% lower.

Jia et al. revealed the basic characteristics of pressure fluctuation caused by the tip leakage vortex, which develops in the clearance between the rotor and stator of axial hydro turbines.

In addition to determining the relationship between the viscous dissipation of tip leakage vortex and the pressure fluctuation, the researchers found the amplitude of pressure change in the core region of the tip leakage vortex was significantly higher than that in other regions.

“This tip leakage vortex research can be widely applied to fluid machinery such as pumps and turbines. It could be entirely possible to improve the hydraulic performance of this equipment as a result,” said author ZuChao Zhu.

Going forward, the researchers will examine tip leakage vortex under different tip clearance sizes, uneven tip clearance, and rough tip clearance.

“After considering these characteristics, what are their pressure characteristics of the flow field in the pump? Do they promote or worsen the energy conversion characteristics of axial flow pumps?” asked Zhu. “These problems are worth exploring.”

Source: “Research on pressure fluctuation induced by tip leakage vortex of axial flow circulating pump under unpowered driven conditions,” by XiaoQi Jia, Hao Lv, Kun Rao, ShuaiKang Zhang, and ZuChao Zhu, Physics of Fluids (2023). The article can be accessed at https://doi.org/10.1063/5.0138842 .