title: Computational Study of Vibration-Based Leak Detection Approach in a 90-Degree Pipe Elbow
titleType: Other
Creators: name: Abuhatira, Ahmed
Publisher: name: University of Dundee
Year: 2022

description: The Vibration-based leak detection (VBLD) approach in pipeline systems has been a topic of research interest. It is identified as effective method for early leak detection and popular choice as its non-invasive and more suited to monitoring than inspection. Most of the previous publications investigated VBLD approach experimentally using a straight pipe with a small diameter in water loop systems.

The current study investigates this approach computationally in the oil and gas sector particularly in a large diameter 90-degree pipe elbow. This task is complex as it involves a combination of the fluid and structure domains. The first part of the task deals with turbulent pipe flow and internal pipe wall pressure fluctuations due to alterations in flow field parameters caused by leaks. The second addresses the external pipe surface vibration response produced by internal pipe wall pressure fluctuations.

The first part of the study presents the use of the wall y+ approach as a form of guidance for reliable selection of mesh and turbulence models in bent pipe flow investigations. The research builds on previous studies recommended by Salim et al.[1]–[3] for using the wall y+ approach to balance between the computational cost and time. This method is proposed as an effective tool for selecting an appropriate near wall treatment and corresponding turbulence model whilst removing the necessity for physical validation when experimental data is unavailable or is difficult to obtain.

Flow in a 90-degree pipe elbow is modelled using the ANSYS FLUENT CFD solver to evaluate the performance of different Reynolds-Averaged Navier-Stokes (RANS) turbulence models. The RANS models tested are the standard k-ε, Reynolds Stress Model (RSM), k-ω Shear Stress Transport (SST) and Spalart-Allmaras models. A range of near wall spatial resolutions is used to determine the effectiveness of near wall modelling techniques when used in conjunction with each of the turbulence models. The near-wall treatments are investigated by solving the y+ values for the first layer of cells in the viscous sublayer (y+≈3), buffer region (y+ ≈19) and log law region (y+≈39). The achieved results in this current study using the wall y+ approach, are compared against experimental data published by Sudo et al.[4] and numerical simulations published by Kim et al.[5]. Qualitative analysis and quantitative assessment are carried out to identify which turbulence model agrees best with the published data.

It is observed that, in comparison with simulations where it is in the buffer and log-low regions, the near wall models provide better results when the y+ values for the first layer of near wall cells are within the viscous sublayer. The RSM predicts the flow field most accurately when compared against the reference data.

In the second part of the research, RSM is coupled with a Finite Element Analysis (FEA) structural model to simulate the Fluid-Structure Interaction (FSI) using one-way coupling. This is to address the second part of the study which deals with the external pipe surface vibration response produced by internal pipe wall pressure fluctuations. The employed RSM turbulence model and subsequent FSI approaches are initially validated against published experimental and numerical results. This is supported by field measurements.

The numerical investigations reveal that the overall vibration signal increases as the flow rate increases. It is observed that the pipe wall experiences high levels of vibration in the centre of the elbow due to drops in pressure and centrifugal forces in that region. The results also indicate that vibration severity increases as the leak size increases. The VBLD is found capable of assessing leakages with different damage severities.

The FSI model developed in this current study can be used to predict the fluid dynamic behaviour inside the pipe and the structure response to this behaviour in a manner that is safer, at a lower cost and less time consuming than a physical study. This in turn will allow pipeline designers to assess the effectiveness of their design, and any potential problems, before the installation stage. It is useful to design experiments within the context of the FSI for pipeline systems including the VBLD. This numerical approach based on FSI and incorporating the VBLD method offers a cost-effective and complementary early-detection tool to use out in the field together with vibration monitoring device.