Numerical modelling for analysing drainage in irregular profile pipes using OpenFOAM

Different methods of two-dimensional and three-dimensional numerical resolution models have been used to predict the air–water interaction in pipe systems in the early twenty-first century, where reliable and adequate results have been obtained when compared with experimental results. However, the study of the drainage process in pressurized systems with air admitted through openings has not been studied using this type of model due to the complexity that this represents. In this research, a two-dimensional numerical model is developed in the open-source software OpenFOAM; this model represents the drainage of an irregular pipe with air admitted by an air valve, defined by a structured mesh. A validation of the numerical model related to the air admitted by the variation of the air valve diameter is also performed. © 2022 Informa UK Limited, trading as Taylor & Francis Group

Numerical modelling for analysing drainage in irregular profile pipes using OpenFOAM

[EN] Different methods of two-dimensional and three-dimensional numerical resolution models have been used to predict the air¿water interaction in pipe systems in the early twenty-first century, where reliable and adequate results have been obtained when compared with experimental results. However, the study of the drainage process in pressurized systems with air admitted through openings has not been studied using this type of model due to the complexity that this represents. In this research, a two-dimensional numerical model is developed in the open-source software OpenFOAM; this model represents the drainage of an irregular pipe with air admitted by an air valve, defined by a structured mesh. A validation of the numerical model related to the air admitted by the variation of the air valve diameter is also performed.Paternina-Verona, DA.; Coronado-Hernández, OE.; Fuertes-Miquel, VS. (2022). Numerical modelling for analysing drainage in irregular profile pipes using OpenFOAM. Urban Water Journal. 19(6):569-578. https://doi.org/10.1080/1573062X.2022.205092956957819

Different Experimental and Numerical Models to Analyse Emptying Processes in Pressurised Pipes with Trapped Air

In hydraulic engineering, some researchers have developed different mathematical and numerical tools for a better understanding of the physical interaction between water flow in pipes with trapped air during emptying processes, where they have made contributions on the use of simple and complex models in different application cases. In this article, a comparative study of different experimental and numerical models existing in the literature for the analysis of trapped air in pressurised pipelines subjected to different scenarios of emptying processes is presented, where different authors have develope, experimental, one-dimensional mathematical and complex computational fluid dynamics (CFD) models (two-dimensional and three-dimensional) to understand the level of applicability of these models in different hydraulic scenarios, from the physical and computational point of view. In general, experimental, mathematical and CFD models had maximum Reynolds numbers ranging from 2670 to 20,467, and it was possible to identify that the mathematical models offered relevant numerical information in a short simulation time on the order of seconds. However, there are restrictions to visualise some complex hydraulic and thermodynamic phenomena that CFD models are able to illustrate in detail with a numerical resolution similar to the mathematical models, and these require simulation times of hours or days. From this research, it was concluded that the knowledge of the information offered by the different models can be useful to hydraulic engineers to identify physical and numerical elements present in the air–water interaction and computational conditions necessary for the development of models that help decision-making in the field of hydraulics of pressurised pipelines

Rapid Filling Analysis with an Entrapped Air Pocket in Water Pipelines Using a 3D CFD Model

A filling operation generates continuous changes over the shape of an air–water interface, which can be captured using a 3D CFD model. This research analyses the influence of different hydro-pneumatic tank pressures and air pocket sizes as initial conditions for studying rapid filling operations in a 7.6 m long PVC pipeline with an irregular profile, using the OpenFOAM software. The analysed scenarios were validated using experimental measurements, where the 3D CFD model was suitable for simulating them. In addition, a mesh sensitivity analysis was performed. Air pocket pressure patterns, water velocity oscillations, and the different shapes of the air–water interface were analysed

Two-dimensional simulation of emptying manoeuvres in water pipelines with admitted air

[EN] This study examines the impact of sub-atmospheric pressures in water pipelines during emptying manoeuvres with air admitted. Previous research has looked at this issue but has not studied it in detail. This research presents a two-dimensional model using the OpenFOAM software to analyse different emptying manoeuvres in a single pipeline with entrapped air. The results show the sensitivity of the ball valve opening percentage, which show that absolute pressure drop can reduce to 23% for each 5% of ball valve opening percentage. The influence of the size of the entrapped air pocket and different air-admission orifices was also analysed. The numerical model showed that the selection of the percentage and times of opening drainage valves in pipelines with air-admission orifices is crucial in controlling sub-atmospheric pressure conditions. Finally, this study demonstrates the ability of the two-dimensional model to show the sensitivity of hydraulic drainage parameters in pipelines with entrapped air.Paternina-Verona, DA.; Flórez-Acero, LC.; Coronado-Hernández, OE.; Espinoza-Román, HG.; Fuertes-Miquel, VS.; Ramos, HM. (2023). Two-dimensional simulation of emptying manoeuvres in water pipelines with admitted air. Urban Water Journal. 20(7):801-812. https://doi.org/10.1080/1573062X.2023.221105380181220

Numerical modeling of rapidly varying flow conditions in collection systems

The design, operation and maintenance of urban water infrastructure depends on the urban runoff flow characteristics. Many modeling tools are being applied for predicting the flow characteristics and their accuracy are essential for more resilient, cost-effective, and safer operation of urban water infrastructures. Engineers and practitioners around the world face difficulties in applying such modeling tools due to the large number of models currently available, the necessary set up parameters, and the required precision to achieve the modeling goals. This research focused in applying well-known models in the context of urban drainage, aiming for improvements in their hydraulic accuracy and in more efficient applications of these models. The Stormwater Management Model (SWMM) is one of the most used tools to simulate different components of urban water systems. Typical unsteady flow conditions are well represented by SWMM, but its capability to precisely simulate more complex phenomena such as regime transition, mixed flows, closed pipe transients, and surges were unknown. The introduction of artificial spatial discretization in SWMM, by increasing the number of computational cells in each link, and the addition of the Preissmann slot pressurization algorithm have the potential to expand SWMM's applications. Hence, artificial spatial discretization and pressurization algorithms were systematically investigated using the conditions presented in the SWMM 5 Quality Assurance Program report. General improvements were achieved in terms of continuity error and numerical stability when artificial spatial discretization was introduced along with the Preissmann slot pressurization algorithm. The rapid filling of collection systems can lead to the development of fast transients, specially caused by unexpected situations such as pump failure or sudden flow blockage. Significant pressure and velocity variations may occur during these events. It was unknown whether SWMM could accurately represent such situations. For this reason, a modification for the new Preissmann slot pressurization algorithm that enforces a celerity value close to the ones anticipated in transient flows was proposed along with artificial spatial discretization. An analytical solution of a hydraulic transient and a model comparison of a real-world situation where a hydraulic transient is expected were used to assess the potential benefits of these modifications. The results demonstrated that SWMM is capable to represent certain types of hydraulic transients when set up accordingly. Stormwater tunnels under rapid filling conditions caused by intense rain events might face operational problems, such as surging. The SWMM capability to represent such situation was never investigated and the addition of artificial spatial discretization as well modifications on the Preissmann slot algorithm are expected to improve SWMM's representation of surging. Using part of the Chicago's TARP tunnel system, a combination of artificial spatial discretization and pressurization algorithms in SWMM was compared to the HAST model, which was specifically designed to represent surges in stormwater tunnels. It was shown that, with adequate model set up, SWMM can represent surging in stormwater tunnels more precisely. Urban areas tend to experience flooding events, especially during intense heavy rain events and/or when the drainage system has limited hydraulic conveyance. Combining a 1D model to represent the key hydrological aspects of the watershed and a 2D model to simulate the flooding extent would enable a better representation of flooding in urban areas as well as faster model set up. Therefore, a 1D PCSWMM was used to represent the surface hydrology and a 2D HEC RAS model was used to simulate the flooding extent based on 1D PCSWMM results. Field data was collected for calibration purposes and possible conceptual approaches that could mitigate the extent of flooding were assessed. This modeling framework predicted the flooded areas according to reported flooding events and it demonstrated that flooding depth and duration was reduced when the conceptual approaches were employed. In large stormwater tunnels, rapid filling conditions may lead to the formation of air pockets and its discharge through vertical structures can cause damages to the system. The pressure variation of uncontrolled air release in complex dropshaft structures was little known. Hence, an investigation of a multiphase rapid filling condition in a tunnel system in Columbus, OH was performed. The methodology coupled a 1D and a 3D model to determine the magnitude of surges, possibility of air pocket entrapment, air–water surging, and the consequences of uncontrolled air pocket release. Results demonstrated that proper ventilation is required to reduce the growth of air phase pressure to safe levels since the air compressibility can cause damages to the dropshaft top slab. Finally, the methodologies proposed in this dissertation improved the accuracy of flow simulation in a range of dynamic, transient, and multiphase flow conditions. We hope that the findings of this research will aid in future applications of simulating flows in collection systems, leading to better operational conditions and greater resiliency

Three-dimensional simulation of transient flows during the emptying of pipes with entrapped air

Two-and three-dimensional analyses of transient flows considering the air-water interaction have been a challenge for researchers due to the complexity in the numerical resolution of the multiphase during emptying in pressurized water pipelines. The air-water dynamic interaction of emptying processes can be analyzed using thermodynamic and hydraulic laws. There is a lack in the current literature regarding the analysis of those phenomena using 3D models. In this research, several simulations were performed to study the complex details of two-phase flows. A 3D model was proposed to represent the emptying process in a single pipeline, considering a PVoF model and two-equation turbulence model. The model was numerically validated through 12 experimental tests and mesh sensitivity analysis. The pressure pulses of the air pockets were evaluated and compared with the experimental results and existing mathematical models, showing how the 3D models are useful for capturing more detailed information, such as pressure and velocity patterns of discrete air pockets, distribution of air and water velocity contours, and the exploration of temperature changes for an air pocket expansion

Two-Phase Flow Simulation in Porous Media Geometries Reconstructed from micro CT Data : Application to Fluid Transport at Low Capillary Numbers

Liquid flow penetrating into porous media, such as rocks, metal foam, soil, and drug delivery, are often simulated as a single phase or multiphase continuum using Darcy’s law. Darcy’s law considered being the most used model of many approaches for simulating the flow through porous media, where the Darcy model assumes a simple proportional relationship between the instantaneous discharge rate through a porous medium, the viscosity of the fluid, and the pressure drop over a given distance. The law was formulated based on the results of experiments on the flow of water through beds of sand. It also forms the scientific basis of fluid permeability used in the earth sciences, particularly in hydrogeology. The underlying assumption with the Darcy method is that the microscopic concept of the liquid flow in any porous material will involve the use of the microscopic velocities associated with the actual paths of the liquid. However, in practice, it is challenging to measure the real microscopic velocities and for this reason, the average value of the real velocities is accepted. By averaging the steady-state Stokes equation this leads to Darcys law, which was introduced as an empirical relationship to describe flow in sand filters, as discovered by Darcy in 1856 and this served as a starting point for numerous practical applications and as a constant challenge for theoreticians. While the original conditions studied by Darcy are found in many practical situations, its extensions to more general cases that are especially designed for theoretical analysis are widely used to represent situations in which experiments are difficult to perform. While this form of Darcy’s law is used with great frequency, it is difficult to get experimental verification of the obvious terms representation of Darcy’s law. For example, the Darcy velocity, which is defined as a volume-average of the flow field, does not represent the real velocity inside the porous media, but rather, the volume of fluid flowing per unit area of the porous medium, including both solids and voids. Also, the pressure gradient does not represent the microscopic pore-level quantity, but rather, is defined over a representative elementary volume medium. To explore Darcy assumptions and to understand the controlling pore-scale mechanisms, a numerical framework has been developed that involves using a reconstructed real porous medium to present a detailed numerical domain for multiphase flow simulations. For the numerical multiphase flow methodology the Volume-of-Fluid (VoF) method combined with additional sharpening, smoothing and filtering algorithms is used as a basis for interface capturing. These algorithms help in the minimisation of the parasitic currents presented in flow simulations. The framework is implemented within a finite volume code (OpenFOAM) using a limited Multidimensional Universal Limiter with Explicit Solution (MULES) implicit formulation. This framework allows for more substantial time steps at low capillary numbers to be utilised compared to the standard solver. In addition, a novel adaptive interface compression scheme is introduced. This allows for dynamic estimation of the compressive velocity only at the areas of interest and thus, has the advantage of avoiding the use of a priori defined compression coefficient parameters. The adaptive method increases the numerical accuracy and reduces the sensitivity of the methodology to tuning parameters. The accuracy and stability of the proposed model are verified against different benchmark test cases. Moreover, the numerical results are compared against analytical solutions as well as available experimental data and this reveals improved predictions relative to the standard VoF solver. This thesis is focused on two different applications that involve porous media: first, flow and transport inside a porous structure, where the presented simulations results show the importance of liquid front invasion. Also, the salience of phase wettability on the residual phase using different wetting dynamic conditions is demonstrated. The results for simulations relating the pore-scale physics, thereby obtaining permeability values are presented. The overall results provide a detailed pore-scale analysis of multiphase flow, serving as a foundation for large-scale modelling and flow prediction. The second application is droplet impact on porous structures and the penetration physics on porous media. The work is focused on droplet spreading and absorption during the early stages of impact. Using the developed framework, the droplet penetrating the porous media is also studied. In addition, simulations of the penetration of different sizes of droplets with different fluid properties in the pore network with different porosities are performed to characterise the effect of the Re and We numbers on the penetration behaviour. The capability to estimate the key features of the flow dynamics has been investigated. For example, in order to relate the microscopic effects to the macroscopic ones, it is important to focus on the maximum spreading, while considering the influence of liquid properties, and wetting behaviour with relation to porous media properties such as porosity. Some conclusions regarding the relation between porosity and porous wall wetting conditions have been drawn using the developed numerical framework for studying the liquid spreading onto porous media. Also, in the thesis, the influence of the porous structure wetting behaviour, the morphology of porous surfaces and the effects of porosity on droplet penetration and spreading are presented. Using the proposed developed solver, a direct relation between penetration volume and the imposed dynamic contact angle was found. This would appear to contradict the expected behaviour in vertical liquid penetration that is obtained using the macroscopic multiphase Darcy’s law. The goals of this research have been achieved by deploying the complex flow physics using the two described applications and by showing the importance of the developed framework in relation to a wide range of applications. This provides evidence for the effectiveness of studying multiphase flows at the microscale level uisng interface tracking methods

Development of an Application-Oriented Approach for Two- Phase Modelling in Hydraulic Engineering

Paralleltitel: Entwicklung eines anwendungsorientierten Ansatzes für die Modellierung von Zweiphasenströmungen im Wasserba