Vortex interaction and wake instability of a propeller under oblique inflow

Oblique inflow modifies propeller wake transition by breaking the symmetry of the helical tip-vortex system and altering vortex interaction. A high-fidelity numerical investigation of the wake dynamics of a propeller under oblique inflow is conducted using the lattice Boltzmann method–large eddy simulation. Simulations are performed at four representative advance coefficients (J = 0.394, 0.591, 0.787, and 0.984) and four inflow angles, including an axial inflow case (β = 0°) and three oblique inflow conditions (β = 15°, 20°, and 25°), to examine the coupled effects of loading condition and inflow angle on wake evolution. The results show that oblique inflow breaks the symmetry of the wake and induces lateral deflection, leading to spatially asymmetric evolution of tip vortices. As the inflow angle increases, vortex trajectories are distorted and brought into closer proximity, which enhances vortex interaction and promotes earlier onset of pairing, merging, and breakdown. Consequently, the unstable wake region shifts upstream and expands in spatial extent. Quantitative analyses of tip-vortex characteristics show that the advance coefficient primarily controls the strength of vortex interaction, whereas the inflow angle governs the asymmetry and instability development. Increasing J weakens vortex interaction and delays vortex breakdown, while increasing β intensifies asymmetric vortex evolution and accelerates the transition toward instability. The unsteady flow characteristics are further quantified in the near-, intermediate-, and far-field wake regions. Velocity fluctuation intensity and power spectral density analyses show that strong vortex interaction leads to amplified fluctuations and rapid spectral redistribution, whereas weaker interaction results in a more gradual transition toward broadband unsteadiness. The results establish that the transition from coherent tip-vortex structures to disordered wake flow is governed by vortex interaction strength controlled by loading, while the inflow angle determines the asymmetric evolution pathway.