PIV Investigation on Lock-Exchange Gravity Currents Propagating Over Roughness Elements

Lock-exchange gravity currents over a rough bottom are investigated through laboratory experiments; PIV technique is used to measure the instantaneous velocity field. The bottom roughness is realized by LEGO® bricks with a constant rectangular section. The main parameter varied is the relative height of the roughness elements to the gravity current depth. The analysis of the instantaneous velocity fields suggests that the presence of the bottom elements modifies the structure of the dense current introducing complexity to the flow dynamics. The streamwise velocity of the gravity current is lower than that observed in smooth surface experiments; the greater the height of the bottom elements, the greater the reduction of velocity. Furthermore, the flow appears dominated by the bottom-generated vorticity due to the presence of recirculation areas between the bricks.