Abstract

The study of the hydraulic behavior of stormwater sewers during intense rain events is motivated by operational problems associated with this rapid filling process they experience. As is well known, intense rain events may trigger the occurrence of pipe-filling bores, which causes flow regime transition between free-surface and pressurized flows and also expulsion of the air within the pipes. In some cases, these bores cause problems such as structural damages to the drainage system and geysering through manholes. Various approaches to promote the numerical simulation of the flow regime transition are available, and some of them incorporate the effects of the air phase within the pipes. In most cases, the modeling of the air phase dynamics is simplified, improving only the calculation of the bore speed changes due to the air pressurization. However, experimental investigations promoted by Vasconcelos and Wright (2004a) demonstrated that the effects of the air pressurization are not limited only to the bore propagation but also contribute to other changes in the flow behavior. In cases when the venting conditions are too limited, the single phase flow approach to modeling system behavior may be insufficient. This work aims to explore the applicability limits of single-phase numerical models for the rapid filling pipe problem using a simplified treatment for the air phase. The numeric code solves the Saint-Venant equations with the Preissmann slot using a finite volume procedure able to capture shocks with minimum numerical diffusion. Air phase description assumes quasi-steady flow, allowing for the development of air pressure gradient within the system. The numerical results of the simulation are compared with available experimental data, and cases in which more complex flow features are developed are discussed. The comparison shows that the proposed model provides a generally accurate description of the flow behavior, and also is able to predict when its applicability would be compromised by the development of more complex flow phenomena.

The study of the hydraulic behavior of stormwater sewers during intense rain events is motivated by operational problems associated with this rapid filling process they experience. As is well known, intense rain events may trigger the occurrence of pipe-filling bores, which causes flow regime transition between free-surface and pressurized flows and also expulsion of the air within the pipes. In some cases, these bores cause problems such as structural damages to the drainage system and geysering through manholes. Various approaches to promote the numerical simulation of the flow regime transition are available, and some of them incorporate the effects of the air phase within the pipes. In most cases, the modeling of the air phase dynamics is simplified, improving only the calculation of the bore speed changes due to the air pressurization. However, experimental investigations promoted by Vasconcelos and Wright (2004a) demonstrated that the effects of the air pressurization are not limited only to the bore propagation but also contribute to other changes in the flow behavior. In cases when the venting conditions are too limited, the single phase flow approach to modeling system behavior may be insufficient. This work aims to explore the applicability limits of single-phase numerical models for the rapid filling pipe problem using a simplified treatment for the air phase. The numeric code solves the Saint-Venant equations with the Preissmann slot using a finite volume procedure able to capture shocks with minimum numerical diffusion. Air phase description assumes quasi-steady flow, allowing for the development of air pressure gradient within the system. The numerical results of the simulation are compared with available experimental data, and cases in which more complex flow features are developed are discussed. The comparison shows that the proposed model provides a generally accurate description of the flow behavior, and also is able to predict when its applicability would be compromised by the development of more complex flow phenomena.

The study of the hydraulic behavior of stormwater sewers during intense rain events is motivated by operational problems associated with this rapid filling process they experience. As is well known, intense rain events may trigger the occurrence of pipe-filling bores, which causes flow regime transition between free-surface and pressurized flows and also expulsion of the air within the pipes. In some cases, these bores cause problems such as structural damages to the drainage system and geysering through manholes. Various approaches to promote the numerical simulation of the flow regime transition are available, and some of them incorporate the effects of the air phase within the pipes. In most cases, the modeling of the air phase dynamics is simplified, improving only the calculation of the bore speed changes due to the air pressurization. However, experimental investigations promoted by Vasconcelos and Wright (2004a) demonstrated that the effects of the air pressurization are not limited only to the bore propagation but also contribute to other changes in the flow behavior. In cases when the venting conditions are too limited, the single phase flow approach to modeling system behavior may be insufficient. This work aims to explore the applicability limits of single-phase numerical models for the rapid filling pipe problem using a simplified treatment for the air phase. The numeric code solves the Saint-Venant equations with the Preissmann slot using a finite volume procedure able to capture shocks with minimum numerical diffusion. Air phase description assumes quasi-steady flow, allowing for the development of air pressure gradient within the system. The numerical results of the simulation are compared with available experimental data, and cases in which more complex flow features are developed are discussed. The comparison shows that the proposed model provides a generally accurate description of the flow behavior, and also is able to predict when its applicability would be compromised by the development of more complex flow phenomena.

The study of the hydraulic behavior of stormwater sewers during intense rain events is motivated by operational problems associated with this rapid filling process they experience. As is well known, intense rain events may trigger the occurrence of pipe-filling bores, which causes flow regime transition between free-surface and pressurized flows and also expulsion of the air within the pipes. In some cases, these bores cause problems such as structural damages to the drainage system and geysering through manholes. Various approaches to promote the numerical simulation of the flow regime transition are available, and some of them incorporate the effects of the air phase within the pipes. In most cases, the modeling of the air phase dynamics is simplified, improving only the calculation of the bore speed changes due to the air pressurization. However, experimental investigations promoted by Vasconcelos and Wright (2004a) demonstrated that the effects of the air pressurization are not limited only to the bore propagation but also contribute to other changes in the flow behavior. In cases when the venting conditions are too limited, the single phase flow approach to modeling system behavior may be insufficient. This work aims to explore the applicability limits of single-phase numerical models for the rapid filling pipe problem using a simplified treatment for the air phase. The numeric code solves the Saint-Venant equations with the Preissmann slot using a finite volume procedure able to capture shocks with minimum numerical diffusion. Air phase description assumes quasi-steady flow, allowing for the development of air pressure gradient within the system. The numerical results of the simulation are compared with available experimental data, and cases in which more complex flow features are developed are discussed. The comparison shows that the proposed model provides a generally accurate description of the flow behavior, and also is able to predict when its applicability would be compromised by the development of more complex flow phenomena.

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