Propeller jet flow scour around pile group supported piers

In this study, scouring formation around pile groups with different configurations and exposed to a ship's main propeller jet flow was investigated experimentally. The experiments were conducted in a flume by installing cylindrical piles on a horizontal sand bed. The selected pile configuration was a 3 x 3 square arrangement. Different tests were performed by changing the space between the piles. The effect of the distance between the piles with respect to the densimetric Froude number (Frd) on scour formation was investigated by considering three different propeller rotation speeds (590, 670 and 745 rpm) with 5 and 7 cm pile diameters (d0), using propellers with diameters (Dp) of 6.5 and 10 cm located 10 cm above the sand bed (G) and 10 cm away from the front piles (X). In addition, the 3D global scour-hole geometry was obtained using photogrammetric data collection and analysis techniques. The equilibrium scour hole morphology was described in detail, and the characteristic dimensions of the resulting scour hole were thoroughly analyzed. The equilibrium scour depth of the pile groups was found to depend on the space between piles (Xt), densimetric Froude number and also position of the propeller. The equilibrium (maximum) scour depths around piles with respect to their configuration were larger than the scour depth around a single pile under same flow conditions.