An experiment is conducted to investigate the characteristics of ventilated cavity flow under a special condition, where the incoming flow direction aligns with the gravity direction in an innovative gravity-driven vertical water tunnel (GVWT). An axisymmetric slender body with well-controlled ventilation is developed to ensure a steady condition of the incoming flow and ventilation. Measurements of cavity geometry and pressure on the cylinder are conducted synchronously. The cavity shape under the streamwise gravity no longer exhibits the spanwise up-floated drift in conventional horizontal water tunnels. Instead, the re-entrant jet evolution and the cloud cavity shedding present pronounced three-dimensional unsteady characteristics along both the circumferential and spanwise directions. The degree of water–air mixing divides the quasi-steady cavity geometry into four distinct zones, identified statistically through extensive image analysis. For a given air flow rate of ventilation, an increase in incoming flow velocity leads to earlier cavity shedding, resulting in a reduction in both the statistical length and outline of the cavity. The pressure fluctuation on the cylinder wall is analyzed in the time and frequency domains. The evolution of pressure patterns is consistent with classic theories of ventilated cavities. Moreover, the pressure coefficient reveals a uniform pressure recovery process through the cavity closure region. The cavity length estimated from pressure data correlates well with that determined from images. This study offers visualized phenomena and critical experimental data for the research on the ventilated cavity under streamwise gravity.
Wang et al. (2025) studied this question.