Velocity Characteristics of a Ship-Propeller Induced Swirling Jet

Thursday 2 july 2015

17:39 - 17:42h at Mississippi (level 1)

Themes: (T) Sediment management and morphodynamics, (ST) Morphodynamics of estuaries and coastal areas, Poster pitches

Parallel session: Poster pitches: 13A. Sediment - Coast

The swirling water jet induced by a propeller poses significant impact on the riverine and marine environments. Erosion around quay structures and contaminant dispersion in harbors or along navigation channels are examples of these effects. Simulating propeller-induced jet velocities that extend from the near to far field is the first step to elucidate the phenomenon and seek solutions. Most previous investigations proposed semi-empirical equations to estimate the velocity under a plane-bed condition. The spatial evolution of the axial velocity downstream of a rotating propeller under movable bed conditions has hitherto received less attention. In this study, the mean and turbulent flow fields downstream of a rotating propeller under both fixed-flat and equilibrium scour bed conditions with static water were investigated. The three-dimensional velocity field was measured by using an acoustic Doppler velocity profiler (ADVP). The experimental results show that the mean velocity and turbulence in the axial, tangential and radial directions all decrease with the increase of distance from the propeller plane. The radial distributions are asymmetrical and the maximum values do not occur on the propeller axis in the zone of flow establishment (ZFE) due to the presence of the propeller hub. The swirl number for the propeller rotation is a function of the maximum axial velocity and tangential velocity. Moreover, both the maximum axial and tangential velocities decay with the increase of distance from the propeller plane. A point-source method, derived from Reichardt's momentum transport hypothesis with the adjustment of jet spreading coefficient, was employed to provide an analytical solution for the axial velocity. By using the concept of superposition, the axial velocity profiles downstream of the propeller both in the flat and equilibrium scour bed were computed and the results, especially for those near to the bed, compared well with the experimental data. Based on results of this study, the axial velocity profile calculated by using the point-source method may be applied to investigate the scour and sediment re-suspension induced by a propeller jet.

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