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Durante los procesos de llenado y vaciado en los sistemas hidráulicos a presión pueden generarse importantes sobrepresiones o depresiones, independientemente de la presencia o no de ventosas. Por ello, el conocimiento físico del problema planteado y la posibilidad de evaluar los picos de presión que potencialmente pueden generarse presenta un indudable interés práctico. Para lograr estos objetivos, es fundamental disponer de herramientas adecuadas y modelos matemáticos fiables y contrastados que permitan la simulación de los transitorios hidráulicos con aire atrapado de la forma más realista posible. En este trabajo se analizan diversos modelos matemáticos para el análisis de los procesos de llenado y vaciado en los sistemas hidráulicos a presión: (i) modelos matemáticos 1D; (ii) modelos simplificados: modelos cuasi-estáticos; (iii) modelos complejos: modelos 2D/3D con técnicas CFD.

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.

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.

The outlet angle and shape of impeller blades are important parameters in centrifugal pump design. There is a lack of detailed studies related to double curvature impellers in centrifugal pumps in the current literature; therefore, an experimental and numerical analysis of double curvature impellers was performed. Six impellers were made and then assessed in a centrifugal pump test bed and simulated via 3D CFD simulation. The original impeller was also tested and simulated. One of the manufactured impellers had the same design as the original, and the other five impellers had a double curvature. Laboratory tests and simulations were conducted with three rotation speeds: 1400, 1700, and 1900 RPM. Head and performance curve equations were obtained for the pump–engine unit based on the flow of each impeller for the three rotation speeds. The results showed that a double curvature impeller improved pump head by approximately 1 m for the range of the study and performance by about 2% when compared to basic impeller. On the other hand, it was observed that turbulence models such as k-e and SST k-w reproduced similar physical and numerical results.

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-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.

[EN] 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-phase transient flows in emptying processes of hydraulic pipelines with entrapped air have been studied in detail in the literature through the development of different mathematical models based on rigid column models. During literature review, it was found that transient flows representing pipeline emptying processes have been rarely studied by two-dimensional and three-dimensional analysis. This research begins demonstrating the behavior of air and water in pipelines during emptying processes, and the formulation of existing mathematical models, where two scenarios are considered: i) Emptying process of a branched hydraulic conduction with air valves, and ii) Emptying process of a simple hydraulic conduction without air valves. In this master thesis, two computational fluid dynamics (CFD) models were developed to study the hydraulic-thermodynamic parameters that occur in pipe emptying processes. An introduction to CFD modeling is performed for its use in the two-dimensional and three-dimensional analysis of two-phase transient flows. Subsequently, a 2D CFD model is performed to simulate Scenario No. 1 (branched hydraulic conduction with air valves), and a 3D CFD model is performed to simulate Scenario No. 2 (simple hydraulic conduction without air valves), described above. The geometric domains, meshing, boundary conditions, numerical schemes and calculation tolerances for the numerical solution of the Navier-Stokes equations for two-phase and compressible flows are defined for numerical processing. The 2D and 3D CFD models are validated with results obtained from experimental measurements carried out by other authors, and by means of a meshing sensitivity analysis. The CFD models show good correlation with the experimental results associated with pressure patterns, velocity, water column length, and allow to visualize in greater detail transient phenomena that are not captured by the mathematical models. These CFD models are compared numerically with their re

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.

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.

Air valves operate as protection devices in pipelines during drainage processes in order to mitigate vacuum pressures and control the transient flows. Currently, different authors have proposed one-dimensional models to predict the behaviour of orifices during filling and draining events, which offer good numerical results. However, the three-dimensional dynamic behaviour of air-admission orifices during drainage processes has not been studied in depth in the literature. In this research, the effects of air inflow on an orifice installed in a single pipe during drainage events are analysed using a three-dimensional computational fluid dynamics model by testing orifices with diameters of 1.5 and 3.0 mm. This model was validated with different experimental measurements associated to the vacuum pressure, obtaining good fits. The three-dimensional model predicts additional information associated to the aerodynamic effects that occur during the air-admission processes, which is studied. Subsonic flows are observed in different orifices with Mach numbers between 0.18 and 0.30. In addition, it is shown that the larger-diameter orifice ensures a more effective airflow control compared to the smaller-diameter orifice

[EN] The rapid filling process in pressurized pipelines has been extensively studied using mathematical models. On the other hand, the application of computational fluid dynamics models has emerged during the last decade, which considers the development of CFD models that simulate the filling of pipes with entrapped air, and without air expulsion. Currently, studies of CFD models representing rapid filling in pipes with entrapped air and with air expulsion are scarce in the literature. In this paper, a two-dimensional model is developed using OpenFOAM software to evaluate the hydraulic performance of the rapid filling process in a hydraulic installation with an air valve, considering different air pocket sizes and pressure impulsion by means of a hydro-pneumatic tank. The two-dimensional CFD model captures the pressure evolution in the air pocket very well with respect to experimental and mathematical model results, and produces improved results with respect to existing mathematical models.

The rapid filling process in pressurized pipelines has been extensively studied using mathematical models. On the other hand, the application of computational fluid dynamics models has emerged during the last decade, which considers the development of CFD models that simulate the filling of pipes with entrapped air, and without air expulsion. Currently, studies of CFD models representing rapid filling in pipes with entrapped air and with air expulsion are scarce in the literature. In this paper, a two-dimensional model is developed using OpenFOAM software to evaluate the hydraulic performance of the rapid filling process in a hydraulic installation with an air valve, considering different air pocket sizes and pressure impulsion by means of a hydro-pneumatic tank. The two-dimensional CFD model captures the pressure evolution in the air pocket very well with respect to experimental and mathematical model results, and produces improved results with respect to existing mathematical model

Los estudios de las presiones subatmosféricas han sido muy detallados en las operaciones de llenado de tuberías, pero su estudio en los procesos de vaciado ha sido muy escaso debido a que se han realizado pocos modelos experimentales y numéricos que predicen dicho fenómeno. Un grupo de autores formularon un modelo matemático con el objetivo de estudiar este fenómeno en el proceso de vaciado acompañado de sus casos experimentales en la Universidad Politécnica de Valencia, España, basado en varias pruebas en una tubería simple de 4.36 metros de longitud, 42 milímetros de diámetro interno, la cual posee una bolsa de aire atrapada aguas arriba cuyas dimensiones son conocidas, y se realizaron unos orificios que simularon la admisión de aire a través de una ventosa. Para la medición de las presiones subatmosféricas de la bolsa de aire se utilizó un transductor de presión para obtener resultados en diferentes condiciones, y posteriormente se comprobó sus respectivos comportamientos a través del modelo en 1D. Para comprobar este fenómeno a través del modelo de dinámica de fluidos computacional (CFD) en 2D, se trabajó en el software OpenFOAM, determinando dentro del mismo las dimensiones geométricas equivalentes, las condiciones de contorno conforme a las condiciones reales en las que se realizaron los casos experimentales, y posteriormente la elección de un modelo turbulento para garantizar mayor precisión en los valores numéricos. De acuerdo con los resultados obtenidos, se comprobó que el comportamiento de la presión de la bolsa de aire en el modelo CFD es similar al comportamiento en los casos experimentales y el modelo matemático propuesto, incluso se convierte en un factor de investigación para la prueba a través de una representación en 3D y su respectiva comparación con estos modelos en cuanto a sus resultados, además de una exploración de diferentes modelos de turbulencia.