Gravity currents
Experiments/Research performed by Rafael Bueno
August 2016 - actual
​
This project is a group of studies investigating the hydrodynamic of gravity currents in stratified and unstratified medias flowing over different topography configuration. A gravity current commonly is a horizontal flow generated by density difference between the gravity current and the ambient fluid.
Gravity current is an important phenomenon that occurs in nature and appears as turbidity currents, overflows, and estuarine effluents. It can also occurs in the atmosphere as katabatic currents end sea breeze. Gravity currents may also be generated by anthropic activities, such as oils spillage, the spread of a gas in the atmosphere, and the pollutant discharge in water bodies.
In the example beside, through the upper figure, apparently the system looks as if it has no dynamic at all, similar to a puddle. Although there is a pollutant discharge in the basin shore, many people believe that the contaminant would be just near that area, and would not be spread through different part of the lake. Actually, the figure bellow shows the complex dynamic of water and sediment within an apparent calm lake.
​
Firstly, the water near the shallower zoner lost heat faster than the deeper part, and consequently the heavier part (colder water) flows over the lake bottom since is heavier compared with the warmer water from the deeper part. Thus, the dynamic of sediment is also influenced by the gravity current. These currents can carry sediment, creating a sediment bank and favor the biomass resuspension. Simultaneously, the gravity current may transfer energy to the thermocline, and depending on the thermal stratification, excites internal waves that travel in the same direction of the gravity current.
This is also observed near rivers. As water coming from rivers are colder, it can also flow at basin bottom or as an intrusion, in within the system, depending on the vertical thermal stratification structure. The pollutant can also have other behaviour, which depends on density of the pollutant.
​
Did you imagine that the pollutant would be transported in that way ? And now, can you predict what will happen with the polutant concentration after this moment ?
​
This depends on many factors, such as the internal wave patterns, the tpography of the system, the gravity current speed and instabilities generates by gravity currents and internal waves activity. The complete undestanding is just possible with a series of laboratory experiments, numerical models and field observbations. This study investigates these phenomena in laboratory tank and through numerical simulations.
​
Note that the figure above presents one possible situation, however this is not always true. Deep basins may present hypolimnion water heavier than the water coming from shallow zones. In addition, the dynamic of sediment also may be different depending on the boundary conditions and chemical compounds that forms the sediment. Bellow we present some findings of our investigations and some published papers.
Finding:
Products :
Bueno, R.; Hoeltgebaum, L.; Colombo, G.; Mannich, M.; Bleninger, T. - Análise experimental da formação de ondas internas gravitacionais a partir de correntes de gravidade. II Encontro Sul Brasileiro de Engenharia Ambiental e Sanitária, Foz do Iguaçu-PR, Brazil, 2018.
​
Hoeltgebaum, L.; Colombo, G.; Bueno, R.; Bleninger, T.; Mannich, M. - Análise experimental da estratificação causada por correntes de gravidade sobre fundo liso e rugoso. II Encontro Sul Brasileiro de Engenharia Ambiental e Sanitária, Foz do Iguaçu-PR, Brazil, 2018.
​
Bueno, R.; Marcon, L.; Wosiacki, L.; Romero, M.; Bleninger, T.; Mannich, M. - Correntes de gravidade e de intrusão produzidas pelo experimento lock-exchange (Gravity currents produced by lock-exchange and intrusion). XXII Simpósio Brasileira de Recursos Hídricos, Florianópolis-SC, Brazil, 2017.