Clear-water scour and flow field alteration around an inclined pile

Abstract

Abstract The present experimental study investigates the scour pattern and the near-wake flow field alteration around an emergent rigid cylinder, which is inclined towards the downstream direction. Three different inclination angles were tested separately, namely 14 ° , 30 ° , and 42 ° with respect to the wall-normal axis. The induced flow and scour patterns were assessed and compared with the well-known case of the emergent upright cylinder (inclination angle 0°). The experiments were conducted for steady flow conditions in a 26 m long recirculating flume and the flow velocity measurements were conducted with an acoustic Doppler velocimeter. For the clear-water scour experiment, a false bed with a sand-pit was installed within the flume and a laser scanner was utilized to render a detailed representation of the scoured bed. The results show how the scouring gets mitigated with increasing inclination angle. Spatial distribution of time-averaged and fluctuation velocity patterns are presented, which exhibit that the vertical mixing gets significantly enhanced behind the inclined cylinder with increasing inclination angle, while the lateral mixing gets weakened at the upper flow region. An upward flow is seen at the immediate downstream of the inclined pile close to the bed, which becomes stronger with the inclination angle. Energy spectra as well as joint frequency distributions of velocity components were analyzed together with the time series, revealing that the inclination of the pile alters the wake significantly. The results further indicate that with increasing inclination angle the pile becomes more streamlined and the vortex shedding gets suppressed.