Mechanisms of energy retention and instability suppression in rotating jets with inlet guide vanes

Rotating jets are widely employed in energy and environmental equipment, and their instability can weaken jet energy-retention characteristics and induce severe energy loss. The regulatory effect of inlet guide vanes (IGVs) on energy retention and instability in rotating jets was investigated using delayed detached eddy simulation, combined with vortex dynamics and entropy production theory. A comparative analysis was conducted between a conventional submersible guided thruster (SGT) and an integrated inlet-guide-vane submersible thruster. Results demonstrate that the IGV-induced counter-prewhirl effectively disrupts the spatial coherence among the tip leakage vortex (TLV), hub vortex (HV), and vortex ring (VR), fundamentally reshaping the energy-transfer pathways. The IGVs strengthen the shear interaction between the HV and the main flow, accelerating HV dissipation and reducing TLV–HV coherence. Quantitatively, the onset of deep instability is delayed from 3.5D to 6.5D downstream, and the peak entropy-production intensity decreases by 22%. In addition, IGV-induced short-wave perturbations promote TLV circumferential breakdown, suppress pitchwise vortex pairing, and nearly eliminate VR-driven HV oscillations. Consequently, approximately 50% of the initial available power is preserved at z/D > 12, representing a 20-percentage-point improvement over the SGT. This study clarifies the dual role of IGVs in regulating jet energy decay and instability, providing guidance for hydrodynamic equipment optimization and energy efficiency enhancement.