Analysis of Sub-Atmospheric Pressures during Emptying of an Irregular Pipeline without an Air Valve Using a 2D CFD Model

Abstract

Studying sub-atmospheric pressure patterns in emptying pipeline systems is crucial because these processes could cause collapses depending on the installation conditions (the underground pipe covering height, type, fill, and pipeline stiffness class). Pipeline studies have focused more on filling than on emptying processes. This study presents an analysis of the following variables: air pocket pressure, water velocity, and water column length during the emptying of an irregular pipeline without an air valve by two-dimensional computational fluid dynamics (2D CFD) model simulation using the software OpenFOAM. The mathematical model predicts the experimental values of the study variables. Water velocity vectors are also analysed within the experimental facility, assessing the sensitivity of the drain valve to different openings and changes in water column length during the hydraulic phenomenon.

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

“…On the other hand, some authors who have developed CFD models to study two-phase transient flows (including emptying operations) highlight the relevant information that these complex models can predict and that the quality of the visual and numerical information is more consistent with what occurs in different experimental cases [8,21,33,37,38]. However, authors who have used CFD models mentioned the complexity of the definition and calibration of these models, as well as the demanding process and computational time required, especially in three-dimensional models, where elements such as (i) the order of solution of numerical schemes, (ii) the algorithm of solution, (iii) turbulence models, (iv) meshing quality, (v) time step and (vi) parallel processing conditions influence the achievement of good numerical and physical results, along with optimisation of computational time.…”

“…Additionally, Besharat et al [7] proposed a two-dimensional CFD model for the analysis of the emptying of a simple pipe with air entrapped inside, where subatmospheric pressure patterns of the air pocket were compared with experimental results of other authors, in addition to predicting deformations of the air-water interface during the event. Authors as Hurtado-Misal et al [21] proposed a 2D CFD model to represent the emptying of an irregular pipe with entrapped air, where the pressure patterns of the air pocket were compared with experimentally measured data and mathematical models proposed by other authors. In addition, authors such as Paternina-Verona et al [22,23] carried out research to study emptying processes with trapped air and air admission orifices using two-dimensional CFD models, which presented a good numerical accuracy compared to experimental results.…”

Effects of Orifice Sizes for Uncontrolled Filling Processes in Water Pipelines

“…It allowed the simulation of fluids in a two-dimensional domain, where the flow profile is considered to have interactions in the horizontal (X-axis) and vertical (Y-axis) directions. Several researchers have obtained excellent numerical and qualitative results using 2D CFD models to simulate air-water interactions in pipes [10,11,16,17,19].…”

“…These 1D models consider an air-water interface perpendicular to the main pipe direction. In addition, 2D CFD models have been implemented to study draining operations with different configurations of water pipelines [10,11]. Moreover, 3D CFD models have been used to model the behaviour of filling processes in water installations [12,13].…”

“…Additionally, these authors analysed the drainage in pipes with entrapped air, comparing pressure patterns with measurements made by other authors and showing the effects of the length of the entrapped air pocket. The authors of [11] developed a 2D CFD model representing the drainage of an undulate pipeline with trapped air, which was compared with numerical results from a mathematical model in [18] associated with the case. Furthermore, the authors in [19] developed a 2D CFD model to simulate the drainage in an undulate pipeline using an approximation of the geometric aspect ratio to represent the behaviour of air valves.…”