Prediction of mean axial velocity of a free turbulent propeller jet

Abstract

Swirling jets induced by propellers have a significant impact on 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 near to far fields is the first step in elucidating this phenomenon and seeking solutions. Most previous investigations have proposed semiempirical equations for estimating velocity. Different formulas have been derived for velocity in both the zone of flow establishment and in the zone of established flow. In this study, the mean and turbulent flow fields downstream from a rotating propeller were investigated using an acoustic Doppler velocity profiler (ADVP). The results showed that the propeller-induced swirling effect was directly proportional to the propeller rotational speed, but decreased as the distance from the efflux plane increased. However, this effect has little effect on the radial distribution of the axial mean velocity and the decay of the maximum velocity. A point-source method was employed, along with the adjustment of the jet axial momentum spreading coefficient, to provide an analytical solution for the axial mean velocity within the propeller jet. Comparisons with measured data from the published literature and from the present study for both flat and equilibrium scour beds showed good agreement. Based on results of this study, the axial velocity profile calculated using the point-source method may be applied to investigate the scour and sediment resuspension induced by a propeller jet.