Author(s): Claudia Adduce, Maria Chiara De Falco and Maria Rita Maggi
Linked Author(s):
Keywords: gravity currents; image analysis technique; bottom obstacle; density fields
Abstract:
Gravity currents are flows produced by a density difference between two fluids. When this difference is due to the presence of suspended sediments a turbidity current occurs. These flows often form during flooding events, when sediments are entrained from the river bed and transported toward a lake or a reservoir, where bottom barriers could be built to stop turbidity currents. In order to investigate the processes occurring between the interaction of a dense current and a submerged barrier laboratory experiments with lock-exchange gravity currents are performed. A first series of experiments, is performed, as base cases, without the bottom obstacle. Then the same experiments are repeated with a triangular barrier and the aspect ratio of the volume of the lock is varied. Lock-exchange gravity currents are produced in a Perspex tank with a horizontal smooth bed and recorded with a camera under controlled light conditions. Dye was added to the gravity current for visualization purposes and an image analysis technique is applied to evaluate the instantaneous density fields. Dye concentration is used as a tracer and for each pixel of the acquired images a calibration procedure is applied in order to relate the concentration of dye, uniformly distributed in the tank, and the greyscale in the corresponding images. In the experiments without the obstacle, the typical structure of a gravity current is detected. When the gravity current interacts with the obstacle, a portion of the fluid flows over the obstacle while the rest of it is reflected back to the left part of the tank. The overflow behaves as a gravity current flowing down a slope and a large interfacial vortex develops at the rear of the head of the current. The gravity current’s dynamics is strongly affected by the presence of the obstacle: the lower is the initial waterdepth, the larger is the obstacle effect and the overflow is able to develop self similar and viscous phases.
Year: 2019