Three-Dimensional Analysis of Air-Admission Orifices in Pipelines during Hydraulic Drainage Events

Abstract

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.

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

“…As with the two-dimensional CFD model described in Section 2 of this research, Paternina-Verona et al [8,24] ensured the numerical solution of the fluid, PVoF, transport and thermodynamic equations using OpenFOAM software v2012 of CFD Direct (ICL, UK) for application on a three-dimensional computational domain. To simulate the turbulence, SST k-ω model was used, based on the advantages of this model mentioned in Section 2.2, taking into account that these equations have been used by other authors to analyse twophase transient flows in three-dimensional CFD models [25,32].…”

“…To that end, Paternina-Verona et al [8] performed an independence analysis of this CFD geometry through the analysis of the numerical evolution of the pressure patterns using different meshes, ranging from 43,500 to 1,220,000, cells with different meshing properties (aspect ratio, asymmetry, orthogonality and computational times), where the numerical results with the different meshes presented a good agreement with the reference measurement used. Finally, in this research, a mesh of 507,375 cells was used for Case 1 and a mesh of 173,500 cells in Case 2 [24].…”

“…The authors of [23] used an experimental setup similar to the single pipe to represent the scenario associated with Case 2 (emptying process with an air admission orifice), where Test C2-1 was compared with the simulation performed by these authors in their research. An analysis of the physical phenomena in Test C2-1 was performed between the results obtained by the 3D CFD model of Paternina-Verona et al [24] and the 2D CFD model of Paternina-Verona et al [23], where the behaviour of the air-water interface and the velocity distribution of the air flow admitted to the hydraulic system through the orifice were compared. Figure 16 showed that the displacement of the air-water interface in the 2D and 3D CFD models was similar at t = 0, 1, 5, and 10 s, and a difference in the location of the air-water interface occurred at the instant t = 15 s, just before total drainage of the water in this test.…”

“…In addition to the backflow air and the deformation of the air-water interface, this model allows obtaining new information such as (i) water flow rates, (ii) transient flows in the pipe cross-sectional, (iii) velocity profiles in different planes, (iv) heat transfer between water and air and (v) analysis of flow parameters with contour view in crosssections [8,24].…”

“…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. Additionally, Paternina-Verona et al [8,24] performed a significant contribution to the three-dimensional analysis of transient two-phase flows in emptying manoeuvres by considering the presence and absence of air admission orifices.…”