No abstract

In this work, the slug flow regime in an air-water horizontal pipe flow has been simulated using the CFD technique. The variables identified to characterise the slug regime are the slug length and slug initiation. Additionally, the pressure drop and the pressure distribution within the simulated pipe segment have been predicted. The volume of fluid method was employed assuming unsteady, immiscible airwater flow, constant fluid properties and coaxial flow. The model was developed in the STAR-CCM+ environment, and the grid was designed in the three dimensional domain using directed mesh. A grid independency study was carried out through the monitoring of the water velocity at the outlet section. 104,000 hexahedral cells for the entire geometry were decided on as the best combination of computing time and accuracy. The simulated pipe segment was 8 m long and had a 0.074 m internal diameter. Three cases of air-water volume fractions have been investigated, where the water flow rate was pre-set at 0.0028 m 3 /s, and the air flow rate was varied at three dissimilar values of 0.0105, 0.0120 and 0.015 m 3 /s. These flow rates were converted to superficial velocities and used as boundary conditions at the inlet of the pipe. The simulation was validated by bench marking with a Baker chart, and it had successfully predicted the slug parameters. The computational fluid dynamics simulation results revealed that the slug length and pressure were increasing as the air superficial velocity increased. The slug initiation position was observed to end up being shifted to a closer position to the inlet. It was believed that the strength of the slug was high at the initiation stage and reduced as the slug progressed to the end of the pipe. The pressure gradient of the flow was realised to increase as the gas flow rate was increasing, which in turn was a result of the higher mean velocity.

The sustainable transportation of liquid fuels in a piping system can be interrupted due to slug flow, which causes the severe unsteady loading on pipelines. A feature that is particularly affected by this problem is the oil transportation pipeline, where gas is often combined with the produced oil. In order to fully understand the behavior of such flows, it is imperative to simulate the effective zones along the span of the pipelines. This will allow the designer of the piping system to estimate the required pumping power through the evaluation of the pressure drop in the slug oil/gas flow. This paper reports the oil/gas flow phenomena in a horizontal pipe with a large diameter of 0.16 m, with 3-dimensional, transient, incompressible fluids, utilizing STAR-CCM+ commercial software. The volume of fluid (VOF) model was adopted to track the interface between the two phases. The operational conditions for the cases studied were extracted for the slug zone from the Baker chart. The slug flow was achieved accordingly, which gives us granted validation with the experimental source. The numerical procedure allowed the determination of the pressure drop. Also, the transient behavior of the slug flow was predicted through the tracking of the slug development in the pipe segment. Moreover, the proposed model could be extended to simulate other types of two-phase flow regimes.

In spite of the fact that it is the most imperative and crucial industry, oil production is still facing problems which represent challenges to producers and operators. This paper presents brief highlights on CFD simulations of some problems associated with oil/water and oil/gas flows carried out by a specialized research team in Universiti Teknologi PETRONAS. Three particular problems have been modelled, simulated and analysed. The first problem is on oil/water mixture flow in the production zone in the downhole; the second is on separation of the oil/water by hydrocyclone separator in the downhole; while the third problem is on the two phase oil/gas flowing in a pipe and the resulted slug flow. For each case, the layout of the procedure of the model setup is explained, and the numerical procedure is outlined in terms of the software used, the mesh generation and its independency criteria. For each case, the validation procedure has been mentioned and in the last part of each case, some samples of results are presented and briefly discussed.

Slug flow regime in two and multi-phase flow in pipes is a complicated flow phenomena representing challenge in the design of the piping system. In the present work, water/air two phase flow was modeled and simulated as 3 dimensional, transient, and incompressible flow using Volume of Fluid technique in STAR-CCM+ software. The simulation was conducted to predict and evaluate the air-water slug flow in a horizontal pipe with 0.16 m diameter and 7 m long. The superficial velocities for both phases were extracted from Baker chart slug zone. The results were validated against experimental bench marking referenced in Baker chart and the proposed VOF technique shows a good capability in simulating the development of the slug flow regime. This model could be utilized for simulation of various two phase flow regimes.

It is well-known that when slug flow occurs in pipes it may result in damaging the pipe line. Therefore it is important to predict the slug occurrence and its effect. Slug flow regime is unsteady in nature and the pipelines conveying it are indeed susceptible to significant cyclic stresses. In this work, a numerical study has been conducted to investigate the interaction between the slug flow and solid pipe. Fluid Structure Interaction (FSI) coupling between 3-D Computational Fluid Dynamic (CFD) and 3-D pipeline model code has been developed to assess the stresses on the pipe due to slug flow. Time – dependent stresses results has been analyzed together with the slug characteristic along the pipe. Results revealed that the dynamic behavior of the pipelines is strongly affected by slug parameters. The FSI simulation results show that the maximum stresses occurred close to the pipe supports due to slug flow, where the pipe response to the exerted slug forces is extremely high. These stresses will subsequently cause fatigue damage which is likely reduce the total lifetime of the pipeline. Therefore a careful attention should be made during the design stage of the pipeline to account for these stresses. The system has been investigated under multiple water velocities and constant air velocity, the maximum stress was obtained at the water velocity of 0.505 m/s. Moreover, when the water velocity is increased from 0.502 to 1.003 m/s the maximum stress magnitude is decreased by 1.2% and when it is increased to 1.505 m/s the maximum stress is diminished by 3.6%.