Comparative study on the energy decay patterns and vortex characteristics of submersible thrusters under different structural configurations

Submersible thrusters (STs) are crucial for applications such as wastewater treatment, but their energy decay mechanisms and flow characteristics remain inadequately understood. This study compares the original ST, a shrouded ST (SGT), and a configuration with both guide vanes and a shroud (SGVT), focusing on energy decay, jet evolution, vortex dynamics, and entropy production. Numerical simulations are conducted using adaptive mesh refinement and delayed detached eddy simulation turbulence models to capture the complex flow structures. Findings indicate that ST undergoes rapid energy decay with pronounced jet energy fluctuations in the transition phase (z/D = 4–8), whereas SGT and SGVT models exhibit slower decay rates, delaying the half-power decay position by 71% and 157.2%, respectively. In the ST jet, vortex interactions, particularly between tip vortices (TVs) and hub vortices (HVs), lead to jet instability, turbulence, and increased entropy production. SGT mitigates centrifugal forces by suppressing tangential velocity, delaying jet instability to downstream regions (z/D = 7). SGVT, by breaking the spiral TV and trailing edge root vortices into smaller-scale vortex clusters and reducing tangential velocity at the blade root, suppresses both TV and HV-induced instability. As a result, the high-entropy production wake width in SGVT is only 50% of that in ST. Instability in the SGVT jet is primarily governed by Kelvin–Helmholtz (K-H) instabilities in the shear layer, which, though weak, support downstream jet propagation. The increased entropy production in SGVT at early stages (z/D = 2–4) is attributed to the formation of small-scale TV clusters.