Analytic and CFD Modelization of Transient Leaking Flows in Pipelines

Significance 

Normally, in most engineering applications, a fluid subjected to high pressure in static conditions such as that kept inside a vessel, is suddenly released through an empty conduit to a lower pressure. The resultant flow has been proven to possess all sorts of complexities. Technically, it can be described as a fast transient with a highly accelerated motion which has a rapidly moving liquid–air interface that converts it into a two-phase flow, and it attains very large Reynolds numbers and an unsteady turbulent regime that deform the mean velocity profiles within the pipeline.

The dynamics of such a flow are challenging to simulate with standard computational fluid dynamics (CFD) codes as most are not designed for reproducing strongly accelerated/decelerated flows. Such flows are thus not frequently studied and therefore have few experimental data available. In addition, not much research regarding CFD simulations of outburst flows such as the aforementioned one is available.

In a recent publication, University of A Coruña scientists: Dr. Francisco Javier García García and Dr. Pablo Farinas Alvarino focused on investigating the transient phenomenon. Their goal was to provide an analytic model (AM) describing the phenomenon’s dynamics. Interestingly, since no experimental data could be sourced from literature, the AM to be simulated was to be used to provide adjustable benchmark data to validate CFD simulations. Their work is currently published in the research journal, Journal of Hydraulic Engineering.

In brief, the authors started by predicting velocity-time curves after which they highlighted the role of adjustable model parameters. Next, a CFD model set to reproduce the AM was devised. They then elaborated on the discretization schemes and pressure–velocity coupling algorithms for the CFD model they had developed. In addition, the requirements for a suitable turbulence model were outlined and the selection of a detached eddy simulation (DES) model was justified. Lastly, they explored the influence of deceleration in the generation of intense turbulence near the wall.

The authors reported that the results produced by the k − ω shear-stress-transport with scale-adaptive-simulation (SSTSAS) turbulence model suggested a thousand-fold increased near-wall turbulence in decelerated flows compared with the equivalent steady-state flows. As such, they were seen to offer clues regarding unsteady velocity profiles not being coincident with the theoretical log-law one. The reported results are compatible with the phenomena of laminarization/turbulentization observed when a pipe flow is subject to acceleration/deceleration, respectively.

In summary, a nontrivial AM was offered with which to compare the performance of CFD codes in applications dealing with unsteady high-Reynolds number flows. The model presented by García and Alvarino described some transient phenomena of interest to engineering applications, namely: Fluidics, fire extinction by the fast discharge of a quenching agent, leakage of fluids immediately after a pipe rupture, release valves activated by excess pressure, air-gun ballistics, and other phenomena in which a liquid is set in motion by the sudden release of a pressurized agent to a lower pressure area. Altogether, the CFD results suggest that deceleration plays a very prominent role in generating turbulence near the wall.

Analytic and CFD Modelization of Transient Leaking Flows in Pipelines - Advances in Engineering Analytic and CFD Modelization of Transient Leaking Flows in Pipelines - Advances in Engineering

About the author

F. Javier García García, PhD, Theoretical Physicist later reconverted to Industrial Engineer, CEO of Integraciones Técnicas de Seguridad, S.A. , member of the Thermal Systems Research Group at A Coruña University, Spain, and member of the Expert Panel of the National Center of Scientific and Technical Evaluation of the Republic of Kazakhstan.

After a short initial period as theoretical physicist researching in Geometric Quantisation, he moved to the field of applied engineering, during which he obtained his MSc in Electronics Engineering while working in companies devoted to electronic instrumentation and measuring systems. Then he specialised in Fire Protection Engineering after being enrolled in multinational firms, and later founded his own company Integraciones Técnicas de Seguridad, S.A., which works actively in complex fire protection applications. While running his company he obtained a PhD degree in Mechanical Engineering, studying the dynamics of fluid discharge to quench fires. Lately he is coming back to Theoretical Physics, and keeps attending the everyday needs of his company.

His company has successfully participated, in team with other companies, in two research projects funded by the ERDF of the European Union. It has also developed and patented the technology known as NeoLIDAR for the real time detection and monitoring of airborne pollution.

Currently, his research interest is related to develop a new theory that explains some of the phenomena observed in transient/unsteady turbulent flows.

ORCID: 0000-0002-8065-1449

SCOPUS ID: 57204879229

About the author

Pablo Fariñas Alvariño, PhD, Naval and Ocean Engineer, professor at the Departament of Naval and Industrial Engineering, and member of the Thermal Systems Research Group at A Coruña University, Spain.

His initial research activities were related to PIV, LDV, and CFD techniques for the study of ship’s hydrodynamics. At the same time, he worked as a Naval Architect and Marine Engineer consultant.

After joining A Coruña University, as a full time professor, his research interest was focused on identifying the mechanism responsible for heat transfer enhancement in nanofluids. In this regard, he joined the Heat Transfer Research Group in the School of Engineering at Sao Carlos, University of Sao Paulo, Brazil.

Currently, his research interest is related to characterisation of turbulent transient flows, and pool boiling phenomena. In addition, he is the person in charge of a research project involving more than 50 people and budget above 2.5 million euros.

Reference

F. Javier García García and Pablo Farinas Alvarino. Analytic and CFD Models for Transient Outburst Flow. Journal of Hydraulic Engineering, 2019, volume 145(3): 04018087.

Go To Journal of Hydraulic Engineering

Check Also

Study of the mechanism by which magnetization reduces dust suppressant usage