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Description
Ship frictional resistance can be reduced by injecting gas beneath the hull, but bubble drag reduction decays downstream injection point through mechanisms that is partly understood. Here, BDR over a ?flat plate is investigated using multiphase model in OpenFOAM-dev, validated against the ?at-plate experiments of Elbing et al. (2008) at three gas injection ?ow rates, Q = 2.55, 4.81 and 9.06 m3/min. Tested over a wider range of ?flow rate and free-stream velocity, the same closures remain physically consistent only within the BDR regime; the validated framework is therefore used, within this regime, to analyse how injection?ow rate and bubble diameter control the drag-reduction response and to link it to the bubbly-layer structure and interfacial-force balance. Increasing Q produces both stronger drag reduction and improved downstream persistence. The bubble-size e?ect is ?ow-rate dependent: sensitivity is greatest between 0.2 and 0.4 mm at low and intermediate Q, whereas at high Q drag reduction deteriorates sharply once diameter increases from 0.6 to 0.8 mm; db = 0.4 mm gives the best agreement with experiment and is adopted as the reference case. Wall-normal air-volume-fraction profiles show that drag reduction is associated with a localized near-wall bubbly layer whose near-wall concentration increases with Q but decays downstream, while the layer itself broadens. Among the interfacial forces, drag and turbulent dispersion dominate the bubbly-layer dynamics; lift and virtual mass act as secondary, localized e?ects, and wall lubrication is negligible.
| Topic Area | Advanced Computational Methods and Applications in Marine, Subsea and Offshore Technology |
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