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This paper investigates air–water interactions during a controlled filling process of an actual water pipeline using a two-dimensional Computational Fluid Dynamics (CFD) model. The main objectives are to understand the dynamic interaction of these fluids through water inflow patterns, pressure pulses, and air-pocket dynamics based on contours. This study uses an existing cast iron pipeline 485 m in length, a nominal diameter of 400 mm, and an air valve with a nominal diameter of 50 mm. The methodology of this CFD model includes the Partial Volume of Fluid (pVoF) method for air–water interface tracking, a turbulence model, mesh sensitivity and numerical validation with pressure and velocity measurements. Results highlight the gradual pressurization of pipelines and air pocket behavior at critical points and show the thermodynamic interaction concerning heat transfer between gas and liquid. This study advances the application of CFD in actual water pipelines, offering a novel approach to air pocket management. [ABSTRACT FROM AUTHOR]

Air exchange in pressurized water pipelines is an essential but complex aspect of pipeline modeling and operation. Implementing effective air management strategies can yield numerous benefits, enhancing the system's energy efficiency, reliability, and safety. This paper comprehensively evaluates an irregular profile pipeline filling procedure involving air-release through an air valve. The analysis includes real-time data tests and numerical simulations using Computational Fluid Dynamics (CFD). A Digital Twin model was proposed and applied to filling maneuvers in water installations. In particular, this research considers an often-overlooked aspect, such as filling a pipe with an irregular profile rather than a simple straight pipe. CFD simulations have proven to capture the main features of the transient event, which are suitable for tracking the air-water interface, the unsteady water flow, and the evolution of the trapped air pocket. Thus, they provide thorough and reliable information for real-time operational processes in the industry, focusing on the filling pressure and geometry of the air-valve hydraulic system. Additionally, this study provides details regarding the application of an efficient Digital Twin CFD approach, demonstrating its feasibility in optimizing the filling procedure in pipes with irregular profiles. [ABSTRACT FROM AUTHOR]

Entrapped air pockets in water pipelines play a significant role in influencing transient over-pressures during filling procedures. Several research is focused on highlighting the attenuation of pressure peaks in pipes with single air pockets. This research studies the air-water interaction during rapid water filling processes in an irregular pipeline and air pockets in different branches, and how the trapped air can attenuate the over-pressure peaks. A three-dimensional computational fluid dynamics (CFD) model was developed, and numerical results of the model were validated through experimental measurements. For a given initial air pocket condition upstream of the high point, the maximum air pocket over-pressure was 11% to 32% lower when the descending pipe segment initially contains air compared to when it contains water. In sum, it was found that entrapped air pockets at high points of water pipelines can help mitigate transient over-pressures considering specific initial hydraulic conditions prior to filling operations. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The sizing of air valves during the air expulsion phase in rapid filling processes is crucial for design purposes. Mathematical models have been developed to simulate the behaviour of air valves during filling processes for air expulsion, utilising 1D and 2D schemes. These transient events involve the presence of two fluids with different properties and behaviours (water and air). The effect of air valves under scenarios of controlled filling processes has been studied by various authors; however, the analysis of uncontrolled filling processes using air valves has not yet been considered. In this scenario, water columns reach high velocities, causing part of them to close air valves, which generates an additional peak in air pocket pressure patterns. In this research, a two-dimensional computational fluid dynamics model is developed in OpenFOAM software to simulate the studied situations. [ABSTRACT FROM AUTHOR]