Laminar cavitation instability under interference and rotational effects

This study investigates the flow characteristics around two infinitely long side-by-side circular cylinders with a spacing ratio s* = 2.3 under cavitating (σ = 1.0 and 0.7) and non-cavitating (σ ≥ 2) conditions at a Reynolds number Re = 200. The study considers four states of cylinders, including stationary and three rotating cases (inward, backward, and mixed) with a velocity ratio γ = 1.5. Hydrodynamic forces, flow instability, and phase modes are analyzed using the two-dimensional laminar transient computational fluid dynamics solver Ansys Fluent. The Zwart–Gerber–Belamri cavitation model is used to capture the unsteady phase-change behavior. The results show that the loads and phase mode are no longer influenced by the gap jet but by the strength and shape of the cavity. Cavitation substantially reduces drag and unsteady fluctuations while retaining reasonable lift. Additionally, cavitation drives a non-monotonic phase sequence, including in-phase or antiphase shedding. In some cases, the phase lag (neither antiphase nor in-phase) or hybrid mode that transitions downstream into a collective single-street wake can be observed. With rotation, cavitation can flip the phase mode and influence whether the vortex street tightens, merges, or is suppressed. To our knowledge, this is the first phase-σ dependence at fixed s* for side-by-side cylinders, revealing cavitation-induced phase transitions without changing spacing or Re.