Effects of wall morphology and hydrogen leakage on hydrodynamic coefficients and wake evolution of flow over a near-wall cylinder

This paper uses open field operation and manipulation to conduct 2D numerical simulations for near-plane-wall and near-wavy-wall bare cylinders at Reynolds number 100 and gap ratios (G/D) 2–5, under leakage and non-leakage conditions, examining how G/D, the wavy wall, and leakage affect vortex evolution and hydrodynamics. The results show that under non-leakage conditions, the quasi-static vortex (QSd) behind the downstream wavy wall shows three types (type 1–3) with varying G/D. Their key difference is the migration pattern of the split vortex (QSd-S). Under the leakage condition, affected by hydrogen bubbles, only type 1 and type 2 QSd-S migration patterns exist. The wavy wall's hydrodynamic influence varies with G/D. Under the non-leakage condition, the critical G/D is 2.5, while under the leakage condition, extending to 3. Compared with the near-plane-wall cylinder, under the effect of the wavy wall, the force coefficients of the cylinder show a decrease in both lift and drag features; when above the critical value, they present an increase in both lift and drag features. Under the leakage condition, three hydrogen migration modes are found, which affect the migration of the lower-side main vortex and the force coefficients, with the competition ranking I > II1 > II2. Under the non-leakage condition, lift and drag frequencies of the near-wall cylinder show dual-frequency vibration and same-frequency coupling. After leakage, multi-frequency fluctuations occur, and the dominant frequency shifts over time. Under the influence of hydrogen bubbles, a drag frequency that is triple the lift dominant frequency emerges.