Gravity Currents Propagating on Sloping Boundaries

Three-dimensional direct numerical simulations of gravity currents on different bottom slopes are presented in this paper. After the buoyancy closed in a lock is instantaneously released, the produced gravity currents go through an acceleration phase followed by a deceleration phase. In the acceleration phase, the tail current connects to and feeds buoyancy into the head for all cases considered here. The maximum buoyancy contained in the head, reached at the end of the acceleration phase, increases as the bottom slope increases. The maximum buoyancy in the head never reaches the total released buoyancy, and a significant portion of released heavy fluid is left in the tail current. In the deceleration phase, the tail current continues to join the head as the gravity currents propagate for lower slope angles (theta = 0.2, and 4 degrees), but the head disconnects the joining tail current for higher slope angles (theta = 6, 8, and 10 degrees). The gravity current head loses contained buoyancy less rapidly in the deceleration phase as the bottom slope increases. Structures of the gravity current indicate that the relative length of the head diminishes as the gravity currents propagate downslope for lower slope angles and remains approximately constant for higher slope angles. The maximum front velocity increases as the bottom slope increases. In the deceleration phase, the front location-time relationship follows the thermal theory power law for higher slope angles and for lower slope angles, and the inertial phase power-law asymptote is observed. (C) 2013 American Society of Civil Engineers.