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Abstract

Geysers in dropshafts of stormsewer systems are consecutive eruptions of a mixture of gas and liquid that can attain heights of more than 30 m. The present study investigates the mechanisms and characteristics of these extreme events numerically using OpenFOAM toolbox. The numerical model is based on a compressible two-phase flow solver and was validated using laboratory tests that achieved large eruption heights. The results show that the aforementioned experimental geysers can be reasonably well simulated using two-and three-dimensional numerical models. Further studies are needed to verify the applicability of two-dimensional models for simulating geysers in actual stormsewer systems. Moreover, the results suggest that compressibility of air plays a critical role in the formation of geysers. Overall, the conducted numerical study provides insights into the characteristics of geyser eruptions and presents some criteria for performing efficient numerical simulations of these events.

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... Most numerical studies simulated geysers that do not resemble the characteristics of geysers produced in actual stormsewer systems. Recently, Chegini and Leon (2019) utilized OpenFOAM (CFD Direct, 2017) for simulating field-scale geysers and with characteristics resembling those produced in actual stormsewer systems. ...
... In the current study, a second order scheme with a flux limiter (Van Leer, 1997) was considered for the spatial discretization and a second-order scheme for the temporal discretization called Crank-Nicolson. Additionally, the maximum Courant number was set to 0.5 (Chegini and Leon 2019). A 3D mesh of the geometry of the experimental setup in Leon et al. (2018) was generated using SALOME (Open Cascade, 2017) and snappyHexMesh, an OpenFOAM meshing utility. ...
Conference Paper
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This paper reports a laboratory and numerical study on violent geysers in a vertical pipe. The laboratory geysers produced consists of a few consecutive violent eruptions within a time frame of a few seconds with heights that may exceed 30 m and with characteristics resembling geysers that occur in actual stormsewer systems (e.g., strongest eruption is not the first one but few eruptions later). In general, the present study shows that once the air pocket breaks through the free surface and produces a water spill, the horizontal pipe flow dynamics, in particular the rapidly changing pressure gradient following the first weak eruption, is driving the entire geyser mechanism. This conference paper is based on the following papers Leon
... It was found that the break-up of the air pocket in the horizontal pipe caused a series of eruptions; the strongest eruption was not the first one, but the later ones. The results were then numerically modelled by Chegini and Leon (2020). The geyser eruption was successfully simulated with detailed flow patterns and air/water interactions. ...
Article
In urban stormwater systems, a rapid increase in water inflow can cause the entrapment of air pockets and subsequent ejection of air/water mixture, commonly known as storm geysers. In this study, a three-dimensional computational fluid dynamics model was built based on a lab model, which consisted of an upstream pipe and a downstream pipe with different invert elevation (i.e., a drop), connected by a chamber with a riser on the top. The effects of the downstream pipe characteristics, location of the entrapped air pocket, and its volume on the pressure variation were examined. With the downstream pipe flowing in full, two mechanisms that possibly trigger geyser events were simulated and experimentally validated: 1) a rapid inflow front in the upstream pipe with the flow changing from free surface flow to pressurized flow, and 2) the air pocket releasing in a pressurized system. For the first mechanism, the pressure surge in the chamber was related to the capacity of the downstream pipe for the increased flow rate. For the second mechanism, a smaller air pocket in the upstream pipe can generate a higher pressure during the geyser event due to the reduced damping effect on the pressure variation. A larger pressure drop was observed for a larger volume of released air. Lower peak pressure was generated for an air pocket closer to the chamber due to the shorter duration for pressure to build up before the air pocket reached the chamber.
... Within a time frame of a few seconds, each geyser is composed of a few consecutive violent eruptions with heights that may exceed 30 m. Different from air pockets that are driven by the buoyant force, their studies point out that the rapidly changing pressure gradient incident to the first weak eruption is the dominant mechanism that drives the entire geyser formation. Chegini and Leon [22] perform numerical simulations of field-scale geysers in drop shafts of storm sewer systems. The governing equations are based on compressible two-phase air-water flow formulations in both two and three dimensions. ...
Article
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Air entrainment at the intake of a bottom outlet often gives rise to air pockets in its conduit and formation of geysers. The outlet in question comprises a bulkhead gate, gate shaft, horizontal conduit, and exit. Operations show that it suffers from appreciable flow fluctuations and blowouts in the tailwater, which leads to gate operation restrictions. For the purpose of understanding the hydraulic phenomenon, both prototype discharge tests and three-dimensional computational fluid dynamics (CFD) modeling of two-phase flows are performed. The operational focus of the facility are small and large gate openings. The CFD results reveal that, with air entrained in the gate shaft, continual breakup and coalescence of air bubbles in the conduit typify the flow. At small openings below 1 meter, the air–water flow is characterized by either distinct blowouts of regular frequency or continuous air release. In terms of geyser behaviors inclusive of frequency, the agreement is good between field and numerical studies. At large openings, the gate becomes fully submerged, and the flow is discharged without air entrainment and blowouts. The paper showcases the air–water flow features in a typical bottom outlet layout in Sweden, which is intended to serve as an illustration of the study procedure for other similar outlets.
... Under certain circumstances, transition between the two flow regimes may occur (i.e., the flow regime transition phenomenon). Following the transition, force exerting on structures changes violently and causes structural damage [1][2][3]. Numerical simulation of flow regime transition can provide substantial information for the design and management of river-crossing bridges, tunnels, conducts and culverts [4][5][6][7][8][9][10]. ...
Article
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Transition between free-surface and pressurized flows is a crucial phenomenon in many hydraulic systems. During simulation of such phenomenon, severe numerical oscillations may appear behind filling-bores, causing unphysical pressure variations and computation failure. This paper reviews existing oscillation-suppressing methods, while only one of them can obtain a stable result under a realistic acoustic wave speed. We derive a new oscillation-suppressing method with first-order accuracy. This simple method contains two parameters, Pa and Pb, and their values can be determined easily. It can sufficiently suppress numerical oscillations under an acoustic wave speed of 1000 ms−1. Good agreement is found between simulation results and analytical results or experimental data. This paper can help readers to choose an appropriate oscillation-suppressing method for numerical simulations of flow regime transition under a realistic acoustic wave speed.
... Under certain circumstances, transition between the two flow regimes may occur (i.e., the flow regime transition phenomenon). Following the transition, force exerting on structures changes violently and causes structural damage [1][2][3]. Numerical simulation of flow regime transition can provide substantial information for the design and management of river-crossing bridges, tunnels, conducts and culverts [4][5][6][7][8][9][10]. ...
Preprint
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Transition between free-surface and pressurized flows is an crucial phenomenon in many hydraulic systems, including water distribution systems, urban drainage systems, etc. During the transition, the force exerted on the structures changes drastically, thus it is meaningful to simulate this process. However, severe numerical oscillations are widely observed behind filling-bores, causing unphysical pressure variations and even computation failure. In this paper, some oscillation-suppressing approaches are reviewed and evaluated on a benchmark model. Then a new oscillation-suppressing approach is proposed to admit numerical viscosity when the water surface is at proximity of conduct roof which has first order accuracy. This approach adds numerical viscosity when water surface is at the proximity of conduct roof. It can sufficiently suppress numerical oscillations under an acoustic wave speed of 1000m/s and is simple to apply. In comparison with two experiments, the simulation results of this method show good agreement and little numerical oscillations. The results in this paper can help readers to choose an appropriate oscillation-suppressing method to improve the robustness and accuracy of flow regime transition simulations.
Article
Full-text available
This paper reports a laboratory study on violent geysers in a vertical pipe. Each geyser produced consists of a few consecutive violent eruptions within a time frame of a few seconds with heights that may exceed 30 m. Herein, the term “violent” is used to distinguish the present work from previous studies, which reported geyser heights that were relatively small compared to the present study. Previous work has speculated that the extreme behavior of geysers is driven by the buoyant rise of the air pocket in the vertical pipe. The present study shows that once the air pocket breaks through the free surface and produces a water spill, the horizontal pipe flow dynamics, in particular the rapidly changing pressure gradient following the first weak eruption, is driving the entire geyser mechanism.
Article
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Supported with laboratory observations, this paper describes the mechanisms that lead to violent eruptions in stormwater and combined sewer systems. This paper also derives the upper limit for the geyser eruption velocity in these systems. The mathematical analysis shows that the maximum velocity of a gas–liquid mixture eruption in a vertical shaft is that of its mixture sound speed. The analysis also shows that the pressure gradient needs to increase substantially for the eruption velocity to approach the air–water mixture sound speed. The derived upper limit for the geyser eruption velocity is assessed using two test cases: a geyser event in a stormwater collection system in Minneapolis and our laboratory experiments.
Conference Paper
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Four frequently used turbulence models, namely k-ε, realizable k-ε, k-ω, and SST k-ω have been used for simulating violent geysers in vertical pipes. The simulations have been performed using OpenFOAM and the assessment of the adopted models has been carried out by comparing the results with a set of experimental data from the literature. The quantities compared are pressure traces at certain locations, geyser height, and snapshots in the horizontal and vertical pipes at various stages during the geysering. The comparison of turbulence models suggests that all of these models predict almost the same geyser height with a difference of less than 2%. Pressure fluctuations predicted by realizable k-ε and SST k-ω models, however, are in better agreement with the data. Additionally, comparison of experimental and numerical snapshots reveals that the flow patterns obtained using the realizable k-ε model matches those of the experiments more closely. Regarding the computation time, k-ε model outperformed other models, as CPU times of k-ω, SST k-ω, and realizable k-ε models were 1.5, 1.2, and 1.1 times that of k-ε model, respectively.
Article
Full-text available
Uncontrolled air pocket release from water-filled shafts can lead to geysering in stormwater systems. Such occurrences are deleterious from public health and environmental standpoints and can cause property and structural damage. Causes, frequency, magnitude, and location of geysering events still are poorly understood and pose practical difficulties to designers regarding how to create dropshafts that are less likely to present this issue. This paper presents results from experimental and numerical investigations on air-related geysers that provide insight into the mechanisms of air release and the displacement of water in vertical shafts. A 302-mm schedule 40 clear PVC apparatus is constructed with the essential features of a stormwater tunnel, and is fitted with vertical shafts with diameters ranging from 0.10 to 0.20 m. Predetermined air pocket volumes are released in the horizontal pipe and eventually reach shafts, causing water displacement and often causing geysers. Kinematics of the air pocket release are measured along with pressures at selected points in the apparatus. These results are used in the calibration of a computational fluid dynamics (CFD) model, which compares well with the experimental measurements. The model subsequently is used in a larger geometry that allows the evaluation of air pocket release kinematics for a wider range of conditions. Findings of this work provide further details on the nature and strength of geysering events, and suggestions for future studies in this topic are also provided.
Article
Full-text available
Uncontrolled air pockets release from water-filled shafts can lead to geysering in stormwater systems. Such occurrences are deleterious from public health and environmental standpoint and can cause property and structural damage. Causes, frequency, magnitude, and location of geysering events are still poorly understood, and pose practical difficulties to designers as to how to create dropshafts that are less likely to present this issue. This work presents results from experimental and numerical investigations on air-related geysers that aimed to gain insight on the mechanisms of air release and the displacement of water in vertical shafts. A 302 mm schedule 40 clear PVC apparatus was constructed with the essential features of a stormwater tunnel, and was fitted with vertical shafts with diameters ranging from 0.10 m to 0.20 m. During these experiments, predetermined air pocket volumes were released in the horizontal pipe, and eventually reached shafts causing water displacement and often geysers. Kinematics of the air pocket release were measured along with pressures at selected points in the apparatus. These results were used in the calibration of a Computational Fluid Dynamics (CFD) model, which compared well with the experimental measurements. The model was subsequently used in a larger geometry that allowed the evaluation of air pocket release kinematics for a wider range of conditions. Findings of this work provide further details on the nature and strength of geysering events, and suggestions for future studies in this topic are also provided.
Thesis
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The study of multi-phase models is a field of great interest in industry and academia. Multi-phase flows are present in hydraulics, petrochemical industry, oceanography, siderurgy, atomic energy and many other human activities. This field is far from being completely understood and the available tools are still in a developing stage. Nowadays the only general models for this kind of problems are the Direct Numerical Simulation or other models based in the physics of fluids. In this scenario, the aim of this thesis is to develop a new model based on the Volume of Fluid method and the Mixture Model in order to solve multi-phase flows with different interface scales and the transition among them. The interface scale is characterized by a measure of the grid, which acts as a geometrical filter and is related with the accuracy in the solution. This coupled model allows to reduce the grid requirements for a given accuracy. Having this objective in mind, a generalization of the Algebraic Slip Mixture Model is proposed to solve problems involving short and long scale interfaces in an unified framework. This model is implemented using the OpenFOAM(R) libraries to generate a state-of-the-art solver capable to solve large problems in High Performance Computing facilities. In addition several other contributions were made regarding to the conceptualization of the Mixture Model, the development of a new Riemann-free solver used to solve mixture problems and a set of tools to help in the implementation process.
Article
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Geyser events have been observed during the filling of large diameter conduits such as CSO storage tunnels which may experience an explosive release of water and air mixtures from a vertical shaft. Previous studies have not focused sufficient attention on the role of air in the process. This dissertation is devoted primarily to the study of large air pockets trapped in a nearly horizontal conduit and their release through a vertical shaft. Field data collected by others was reviewed and it is concluded these geysers cannot be explained by single phase water flow alone. An alternative explanation involving the release of large air pockets is offered. The propagation and reflection of hydraulic bores is one mechanism by which large air volumes can become trapped in an otherwise water-filled conduit. Experiments demonstrate the interaction of multiple bores resulting in the formation of several air pockets which interact in succession at a vertical shaft to lift water significant vertical distances. Additional experiments involved either the continuous injection of air or the release of a single large air pocket in a horizontal conduit to investigate the air dynamics at an attached vertical shaft. The arrival of the leading edge of the air pocket at the shaft pushes water upwards ahead of it and small diameter shafts are particularly susceptible to large vertical rises, especially with air pockets larger than the liquid volume in the shaft. Numerical modeling is presented to confirm this observation. The vertical rise following the expulsion of an air pocket is demonstrated to primarily be an inertial surge process.. The situation is more complex when multiple air pockets are present in the pipeline since the release of one pocket can influence the behavior of subsequent ones. A modest expansion of the diameter a short distance above the connection with the tunnel was found to provide reductions in water rise. Extending conclusions to large scale systems is difficult due to the inability to produce a process known as flooding in air/water exchange flow. This dissertation demonstrates the need to consider both vertical air/water interactions and horizontal dynamics during system design.
Article
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Below-grade storage tunnels in stormwater systems are usually designed to operate in a free-surface flow regime. However, intense rain events may trigger flow regime transition to pressurized flow, which results in operational problems. To date, little guidance is available as to the considerations necessary to properly design a system undergoing flow regime transition. In this investigation, an experimental apparatus consisting of a 14.6-m -long, 94-mm -diameter acrylic pipe was used to observe the nature of flows in such conditions. It was noticed that the air near the pipe crown may pressurize and influence the flow dynamics. Qualitative observations regarding the interactions between the air and water phases during the filling events are included in this study. Generally the surge intensity was maximized when a hydraulic bore propagating towards the surge riser just filled the pipe cross section, and it increased with the pressure head behind the pressurization front. Furthermore, the results indicate that the effects of air phase pressurization should be properly included in numerical simulations if ventilation conditions are limited.
Article
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Events that are referred to as geysers have been observed in storm-water or combined sewer systems and are associated with jets of water rising through manholes to a considerable distance above the ground surface. Visual observations suggest that air may be a significant component of the jet. The mechanisms of geyser occurrence have been previously assumed to originate in inertial oscillations that force water up through vertical ventilation shafts. Recent laboratory investigations indicate that geyser formation is associated with the release of trapped air pockets through partially filled vertical shafts. Pressure data from a storm-water tunnel subject to infrequent geyser events is presented to indicate that measured piezometric heads adjacent to the ventilation shaft never increase to levels approaching the ground surface during a geyser event suggesting that air interactions must be an important part of the process. It is concluded that system design to avoid geyser formation must include the consideration of trapped air within the tunnel system.
Article
Full-text available
One potential problem affecting below-grade storm-water storage tunnels is the occurrence of geysering, which is defined as the return of conveyed water to grade. Most investigations to date have linked this occurrence with inertial oscillation of the water within vertical shafts. Another mechanism that can lead to geysering is the release of air and water through ventilation towers. This study presents a systematic investigation on geysering caused by the release of large air pockets through partially water-filled ventilation towers. Parameters considered in the study included the water level in the ventilation tower, air-phase pressure head, and ventilation tower diameter. An important parameter in geysering was the diameter of the ventilation tower. A simplified numerical model was developed to simulate the experiments; it was able to reproduce the essential features of the experiments.
Article
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A method of second-order accuracy is described for integrating the equations of ideal compressible flow. The method is based on the integral conservation laws and is dissipative, so that it can be used across shocks. The heart of the method is a one-dimensional Lagrangean scheme that may be regarded as a second-order sequel to Godunov's method. The second-order accuracy is achieved by taking the distributions of the state quantities inside a gas slab to be linear, rather than uniform as in Godunov's method. The Lagrangean results are remapped with least-squares accuracy onto the desired Euler grid in a separate step. Several monotonicity algorithms are applied to ensure positivity, monotonicity and nonlinear stability. Higher dimensions are covered through time splitting. Numerical results for one-dimensional and two-dimensional flows are presented, demonstrating the efficiency of the method. The paper concludes with a summary of the results of the whole series “Towards the Ultimate Conservative Difference Scheme.”
Article
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The introduction of nonlinear, shock-capturing schemes has improved numerical predictions of hydraulic bores, but significant numerical oscillations have been reported in the predictions of pipe-filling bore fronts associated with the transition between open-channel and pressurized flow regimes. These oscillations can compromise the stability of numerical models. A study of these oscillations indicates that the strength of the numerical oscillations is associated with the sharp discontinuities in the flow parameters across the jump, particularly the wave celerity. Approaches to attenuate oscillations by artificially reducing acoustic wave speeds may result in the loss of simulation accuracy. Two new techniques to attenuate the oscillation amplitudes are presented, the first based on numerical filtering of the oscillations and the second based on a new flux function that judiciously introduces numerical diffusion only in the vicinity of the bore front. Both approaches are effective in decreasing the strength of the numerical oscillations.
Article
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The hydrodynamics of a dropshaft-drift tube system under two transient conditions, namely, rapid increase of dropshaft inflow and strong main tunnel surge, is studied analytically and numerically. The governing equations are derived, and then linearized to explicitly represent the system's responses to external disturbances. The linearized study shows that the water column in the dropshaft oscillates sinusoidally in response to a disturbance. The amplitude of the oscillation was found to increase with the strength of disturbance as well as the fundamental period of the system. For inflow-caused disturbances, a typical dynamic instability phenomenon exhibited by growing amplitude of oscillations may exist under certain conditions. For both types of disturbances, the amplitude can be so large that water in the dropshaft may overshoot the ground surface, causing damages. The analytical results are verified by direct numerical solutions of the original nonlinear equations and field records.
Article
Geysers are explosive eruptions of air-water mixture from manholes in drainage systems. When the design capacity of urban storm water drainage systems is exceeded during extreme rainfall, rapid inflows into the drainage network can lead to air-water interactions that give rise to geyserscausing damage to the water infrastructure and threatening human lives. Although extensive research has revealed the role of entrapped air in causing large pressure transients in drainage tunnels, the mechanism of geyser formation remains elusive. In this study, an unsteady three-dimensional (3D) computational fluid dynamics (CFD) model is developed to simulate the pressure transients and air-water interactions during geyser events using the volume-of-fluid (VOF) technique. Extensive numerical simulations are conducted to study the air-pocket dynamics caused by release of trapped air from a horizontal tunnel into a vertical riser. Model predictions of the air-water interface in the vertical shaft are in good agreement with laboratory measurements by a high-speed camera; the mechanism for the formation of geysers is elucidated. It is found that during a geyser event, compression of the air pocket in the riser can lead to rapid acceleration of the overlying water column and its expulsion from the riser; the air-pocket pressure is significantly higher than the hydrostatic pressure of the overlying water column, and the velocity is greater than that of a Taylor bubble. Comprehensive numerical modeling has been conducted to study the effect of the vertical shaft diameter, the upstream pressure head and the air-pocket volume on the air-pocket dynamics; the results show that geyser formation is primarily controlled by the riser to tunnel diameter ratio, D-r/D. 3D CFD simulations have also been carried out for an idealized prototype drainage system; it is shown that the geyser behavior can be characterized by extremely large vertical air velocities that result in dispersed air-water mixtures often observed in the field. (C) 2017 American Society of Civil Engineers.
Article
Geysers are explosive eruptions of air-water mixture from manholes in drainage systems. When the design capacity of storm water drainage systems is exceeded during heavy rainfall, rapid inflows can lead to air-water interactions that give rise to geysers, causing damages and threatening human lives. Over the past two decades, the dynamics of air pockets in vertical shafts and horizontal pipes has been extensively studied. Although the role of entrapped air in causing large pressure transients is revealed, the mechanism of geyser formation remains elusive primarily because of the lack of detailed observations. A comprehensive series of experiments has been performed on a physical model of a simplified drainage system, which consists of a vertical riser and a horizontal pipe with diameter D connected to a constant head tank. The system is filled with water; an air pocket is then released into the horizontal pipe and the trajectories of the air pockets in horizontal pipe and vertical riser are measured by videos and a high speed camera. Pressures are measured using pressure transducers near the pipe end and at the bottom of the riser. Parameters considered include riser diameter (Dr), upstream head (H0), and initial air pocket volume (Vair ). Without an external pressure head, the air pocket migration in a water-filled vertical riser is found to be similar to a slug flow. The rising velocity of the air pocket relative to the free surface (vnet) is nearly constant and close to the speed of a Taylor bubble; no geyser is observed. When an external pressure head is applied to the horizontal pipe, two types of flow are observed. For large riser diameter and small air volume, the rise of the air pocket in the vertical riser resembles a Taylor bubble, with an air pressure equal to the hydrostatic pressure of the water column above. The air breaks within the riser and no geyser is observed. For small riser diameter and large air volume, the horizontal air pocket shoots past the riser junction and only partially enters the shaft; the vertical air pocket migration is very different from that of a Taylor bubble. The air pocket pressure is found to be significantly higher than the hydrostatic value, resulting in rapid acceleration of air and water, and jetting out of air-water mixture from the riser top. Experimental results show that geysers are more likely to occur for small risers (Dr/D ≤ 0.62) and large air volumes (Vair/[(πDr²/4)H0] ≥ 3.42).
Article
Various unsteady or transient models have evolved in order to help engineers achieve economy of analysis, design, construction, operation and maintenance. The specific usage of each model is strongly dependent on the level of unsteadiness in the system and on the accuracy, assumptions and limitations of the applied mathematical model and its numerical solution. Although the research literature is quite clear on these issues, there is often much confusion in practice. In this paper, the key practical differences and advantage for the four transient models — water hammer models, rigid water column analysis, quasi-steady analysis and so-called Joukowski approach — are compared and contrasted with respect to three criteria: their physical attributes, the hydraulic predictions they lead to, and the related numerical considerations of stability and accuracy. A useful guideline for determining the degree of unsteadiness is presented and then linked to an appropriate unsteady model.
Article
The hydraulics of the surcharged flow as well as the open-channel flow leading to and after surcharge is discussed in detail and formulated mathematically. The transition between open-channel and surcharge flows is also discussed. This information is useful for those who intend to make accurate advanced simulation of sewer flows. In this study an approximate kinematic wave-surcharge model called SURKNET is formulated to simulate open-channel and surcharge flow of storm runoff in a sewer system. An example application of the model on a hypothetical sewer system is presented.
Article
This paper presents a numerical investigation of a plunging wave impact event in a low-filling depressurised sloshing tank using a compressible multiphase flow model implemented in open-source CFD software. The main focus of this study is on the hydrodynamic loadings that impinge on the vertical wall of the tank. The detailed numerical solutions compare well with experimental results and confirm that an air trapped plunging wave impact causes the vertical wall to experience pulsating pressure loadings in which alternate positive and negative gauge pressures occur in sequence following the first applied pressure peak. The strongest pulsations of the pressure are found to be near the air pocket trapped by the water mass. The instantaneous pressure distribution along the vertical wall is nearly uniform in the area contained by the air pocket. The phases of pulsating pressures on the wall are in synchronisation with the expansion and contraction of the trapped air pocket. The pocket undergoes changes in shape, moves upwards with the water mass and eventually breaks up into small parts. A careful integration of the wall pressure reveals that the vertical structure as a whole experiences pulsating horizontal impact forces. It is found that the average period of pulsation cycles predicted in the present study is around 5 ∼ 6 ms, and the loading pulsations are quickly damped out in 0.1 ∼ 0.2 s. Further exploratory investigation of the fluid thermodynamics reveals that the temperature inside the trapped air pocket rises quickly for about 2 ms synchronised with the pocket’s first contraction, then the generated heat is rapidly transferred away in around 3 ms.
Article
A comparative performance analysis of the CFD platforms OpenFOAM and FLOW-3D is presented, focusing on a 3D swirling turbulent flow: a steady hydraulic jump at low Reynolds number. Turbulence is treated using RANS approach RNG k-ε. A Volume Of Fluid (VOF) method is used to track the air–water interface, consequently aeration is modeled using an Eulerian–Eulerian approach. Structured meshes of cubic elements are used to discretize the channel geometry. The numerical model accuracy is assessed comparing representative hydraulic jump variables (sequent depth ratio, roller length, mean velocity profiles, velocity decay or free surface profile) to experimental data. The model results are also compared to previous studies to broaden the result validation. Both codes reproduced the phenomenon under study concurring with experimental data, although special care must be taken when swirling flows occur. Both models can be used to reproduce the hydraulic performance of energy dissipation structures at low Reynolds numbers.
Conference Paper
A geyser in a closed conduit system is characterized by an explosive release of a mixture of air and water through a drop shaft. Geysers are often observed in combined sewer systems (CSSs) as an explosive form of combined sewer overflows (CSOs). In the present work, the flow characteristics of sewer geyser phenomenon are studied numerically using a three-dimensional computational fluid dynamics (CFD) model for the first time. Traditionally, investigations of flow processes associated with sewer geysers are conducted through physical experiments and one or two-dimensional numerical models. However, sewer geysers are undeniably three-dimensional, hence 3D models are necessary to gain further understanding of the phenomena. The CFD model was calibrated using an experiment that exhibit characteristics of sewer geysers.
Article
The present paper is concerned with a noniterative method for handling the pressure-velocity coupling of the implicitly discretized fluid flow equations. The method, called PISO (pressure-implicit with splitting of operators), utilizes the splitting of operations in the solution of the discretized momentum and pressure equations. The fields obtained at each time step are close approximations of the exact solution of the difference equations with a formal order of accuracy of the order of powers of delta t depending on the number of operation-splittings used. The method is cast in a time-dependent form. It is, however, also useful for steady-state calculations due to its stability for fairly large time steps. An outline of PISO is presented, and its accuracy is assessed. Attention is given to the transport equations, the finite-difference formulation, the methodology for incompressible flow, boundary conditions, a generalization to compressible flows, and a generalization of the method to other equations.
Article
One of the least understood aspects of flow in sewers is the nature of the transition from gravity to pressure or surcharged flow. A complete design of a storm sewer should consider both gravity and surcharged conditions. The available design and/or simulation models can handle gravity (open-channel) flow with various degrees of sophistication, whereas some consider surcharged flow. None of the available stormwater computer models include an adequate treatment of the transient pressures associated with surges that can occur at the transition from gravity to pressure flow. During the transition period there is a further complication because there is a mixture of air and water in the pipe.This paper deals with transients that occur when gravity flow is suddenly changed to pressure flow by the occurrence of a surge in the line. The pressure head fluctuations associated with this transient have been studied. Some of the factors affecting the pressure transients are: pipe size, pipe shape, flow velocity, Froude number, relative depth of flow, alignment of the pipe, pipe material, venting arrangements, and boundary conditions such as pumps, interceptors, and drop pipes. The paper also suggests a theory to predict the excess pressure rise due to these transients. Keywords: Fluid transients, gravity flow, instability, pipe flow, sewers, surcharged flow, surges, two-phase flow.
Article
This work presents the numerical results obtained when staggered and collocated grids were used in the finite-volume methods (FVMs) for four standard flows: developing laminar single-phase flow at the entrance of the tube; developing turbulent single-phase flow at the entrance of the tube; incompressible laminar flow through an orifice plate; and developing turbulent gas–solid flow in a vertical pipe. These test cases were chosen to embody a variety of pattern flows very common in computational fluid dynamics problems (CFD problems). The main aspects analyzed were: the convergence rate, the stability of the pressure–velocity coupling; the dependence of the solution on the grid concentration and on the variation of the under-relaxation parameters; and the capability of reproduction of the experimental data and/or analytical solutions. The paper also presents a discussion of the strategies to apply the collocated and staggered grids and some aspects of the pressure–velocity coupling for both procedures. The numerical results were compared with experimental data or with analytical solutions and they presented a good agreement. The results show that the staggered arrangement of the grid has an advantage when dealing with high pressure gradient and multi-phase flows.
Article
A new k-[epsilon] eddy viscosity model, which consists of a new model dissipation rate equation and a new realizable eddy viscosity formulation, is proposed in this paper. The new model dissipation rate equation is based on the dynamic equation of the mean-square vorticity fluctuation at large turbulent Reynolds number. The new eddy viscosity formulation is based on the realizability constraints; the positivity of normal Reynolds stresses and the Schwarz' inequality for turbulent shear stresses. We find that the present model with a set of unified model coefficients can perform well for a variety of flows. The flows that are examined include: (i) rotating homogeneous shear flows; (ii) boundary-free shear flows including a mixing layer, planar and round jets; (iii) a channel flow, and flat plate boundary layers with and without a pressure gradient; and (iv) backward facing step separated flows. The model predictions are compared with available experimental data. The results from the standard k-[epsilon]
Article
Thesis (Ph. D.)--University of London, 1997.
7/3/1999 full raw traffic camera catching explosive storm sewer flooding -full video
  • Mn Dot
MN Dot (1999). 7/3/1999 full raw traffic camera catching explosive storm sewer flooding -full video (Technical report). Youtube.
London: The OpenFOAM Foundation Ltd
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Imperial College of Science
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