Author(s): Yanqing Lu; Ling Zhou; David Ferras; Capucine Dupont; Qianuxun Chen; Saber Nasaoui

Linked Author(s): 83453(Yanqing Lu)

Keywords: Geysers; Two-phase flows; Air-water interactions; Physical experiments; Water distribution systems

Abstract: Water distribution systems, essential to industry and daily life, are faced with risks including geysers due to transient hydraulic events such as rapid pipe filling. Hydraulic safety control thus always takes precedence, necessitating rigorous fundamental theories and precise numerical models as a non-engineering management measure. However, current research on geysers often fail to accurately capture and explain the complex two-phase flow dynamics both in pipes and vertical shafts. To address these problems, this study proposes a systematical combination of physical experiments, adopting the typical case that upstream water rapid fills into the empty and dead-end pipe system. Firstly, experiments focus on the mechanism characteristics of air-water interactions of mixed flows in slightly inclined pipes are carried out, which lays a foundation for understanding pressurized air-water mixture in a single pipe. Subsequently, the complex single and two shafts geysers dynamics are clarified in experiments. Lastly, the dynamics of air-water interactions of simple vertical flows are explored, serving as an innovative basic study for the performance for geysers. The results reveal that big air pockets in closed single pipe have obvious air cushion effect, and can exert additional air pressure on the cross-sect apart from water pressure. As one shaft is considered, the geyser erupts fiercely with a high speed two-phase mixture rushing into the shaft, and strengthens the first pressure peaks in pipes, especially the downstream part. Smaller shaft diameter and downstream location lead to bigger geyser eruption height in the considered dead-end water filling scenario. Two shafts at upstream and downstream have little effect on the downstream geyser pressures but much decrease the upstream pressure peaks. Furthermore, it is confirmed in separate vertical flow experiments that the flow regime of geysers in vertical shafts mainly is the churned flow, because of the high water and air surface velocity. In transient process, air pocket rushes into the shaft contribute to the various speed Taylor bubble flow. The high water flow rate may disperse the bubbles and disturb the typical flow regimes, while the wave interference may contribute to local bubble merge and disperse in geysers. With smaller shaft diameter, lower water flow rate, higher air flow rate and pressure, the flow regimes in geysers are clearer as the first eruption with accelerated Taylor bubble, followed with churned flow in shafts. The implementation of this study could provide substantial support for hydraulic safety control, optimal design and emergency dispatching of water distribution management.

DOI: https://doi.org/10.64697/978-90-835589-7-4_41WC-P1843-cd

Year: 2025