Mitigation Strategies to Reduce Detrimental Effects of Air Bubbles in Shaft Spillways: A Literature Review

Abstract

The air is trapped in spillways, pipelines, conduits, and channels which leads to air-water flow and the accumulation of air bubbles that can form large air pockets. These air pockets can cause significant structural failures due to the dynamic consequences they induce. Consequently, this paper investigates the incidents and events that occur due to air pocket formation and measures and strategies to mitigate these issues. The investigation was conducted independently based on a literature review. The literature review focused on interpreting the mechanisms involved in the production of air bubbles and air pockets in pipelines. The research comprehensively examined all occurrences and adverse outcomes associated with the formation of air pockets, including the slug flow phenomena, air entrainment, and air blowout incidents. Moreover, this study reviewed all measures and strategies to mitigate the consequences resulting from air bubbles, such as slug flow management, air management techniques, air pocket explosion, and air entrainment. The results of the literature review showed a lack of predictions of air pocket consequences. Furthermore, the majority of the research conducted relies on prior datasets, observations, and experimental tests. However, these studies are unable to adequately demonstrate the limitations associated with the occurrence of air pockets in hydraulic structures. This is mostly owing to the challenges and constraints in managing the boundary conditions within physical models. Also, all experimental studies addressed the air pocket formation only in pipelines, and there was a lack of studies on the consequences of air pockets in hydraulic structures such as spillways and tunnel systems. Additionally, there was a lack of studies that address CFD techniques using developed software such as ANSYS; these techniques have proven their abilities to predict several consequences caused by air pockets. CFD techniques can simulate any complex problem correlated to air pocket events. This study can address air pocket consequences in any hydraulic structure: Morning Glory spillways, key piano spillways, and drop shaft spillways. Furthermore, this technique can adopt various parameters and extend measures and strategies to mitigate air pocket formation in hydraulic structures. The paper recommends the use of the CFD technique for further studies in the field of air pocket mitigation. Also, as a result of spillway structures, especially Morning Glory spillways, the paper recommends executing further research to predict consequences resulting from air pockets in hydraulic structures and investigate more remedial strategies to mitigate these consequences.