This paper employs a combined experimental and numerical approach to investigate the influence of airflow characteristics—specifically air velocity νa and air density ρa—on the evolution of water-entry cavities at low Froude numbers (Fr<13). A custom-designed test platform enables control over air density ρa and water-entry initial velocity V0. The velocity V0 influences the cavity expansion rate, which in turn determines the air inflow velocity νa into the cavity. Based on the experimental results, a critical condition for surface seal is proposed: ρ*·Fr c 2.62 =315, where ρ*=ρa/ρ0, ρ0 is the ambient density. For constant air density, deep seal dynamics exhibit negligible direct sensitivity to airflow when the Fr < Frc, aligning with classical inertial theories and a 1/2-power scaling law during radial collapse. As ρ* or Fr increases beyond the critical threshold, the cavity closure mode transitions from deep seal to surface seal. Numerical simulations, based on finite volume method, reveals that when the flow field is approximately uniform, the ratio of air flow velocity νa to projectile velocity ν is ~1.5. Furthermore, the airflow-induced pressure difference basically satisfies Δp = ρaua2/2, driving inward splash motion. Neglecting the change in projectile velocity, there is Δp ∝ ρaV02/2. When the splash is about to close, the flow field distribution is relatively complex, and the pressure relationship no longer holds consistently. Surface seal blocks the connection between the cavity and the external atmosphere, directly impacting the internal pressure dynamics and further influencing the deep seal characteristics.
