The main goal of the present work is to establish the analysis of a numerical turbulent simulation of an axial pump cascade under two-phase flow presence of liquid and gas, coupled with the “κ-ε” turbulent model. This knowledge is very important for different applications, for example in the oil industry. Indeed, the transport of two-phase flow (oil and gas) that comes from the well implies the utilization of separation and treatment facilities before pumping. It means that a number of economical resources are involved in this kind of industrial operation. Therefore, depending on the function optimization of this type of two-phase pump, it would permit the substitution of the traditional expensive facilities, in addition to energy cost savings. In order to predict the fluid dynamics characteristics of an axial pump cascade under two-phase flow conditions with a view to improving its performance, the present research will describe a multifluid model in order to solve the momentum equations (Navier-Stokes) coupled with the continuity equation. Here, we will use a modified “κ-ε” turbulent model, taking into account the viscosity of the liquid phase and the compressibility of the gas phase, using the CFD simulator: CFX-4.0. As a consequence of this numerical simulation, we will be able to optimize the design of a cascade of an axial two-phase pump and therefore obtain its optimum point of operation.
Multiphase pumping has consolidated itself as the state of the art technology in crude oil transport for declining and marginal fields. Several types of pumps have been applied or developed for such service, opening a new research trend worldwide. In this research we studied the progressive cavity pump performance with two-phase flow. Our aim was to obtain the pressure and temperature profiles along the pump's stator, and to observe its behavior under different sets of variables such as gas void fraction, rotational speed and Ap. The knowledge that can be acquired will be useful to estimate how flow conditions can be affecting the pump's life and the smoothness of the pump performance. The results showed that for single-phase flow at low Ap the maximum pressure is not located at the pump outlet as it would be expected. The pressure distribution in the pump with two phase flow is completely different to the latter case, being found that within the pressure range of the experiment the cavities are kept sealed almost along the whole pump. For any point of operation the maximum temperature is found in the intermediate stages.
Cavitation is a common phenomenon that appears during the operation of the hydraulic turbomachines reducing performance and life of Centrifugal pumps. The main goal of this work is primarily a CFD-simulation of the whole Centrifugal Pump-Turbine including the suction cone, impeller, diffuser blades and volute, in order to characterize and evaluate its performance under cavitation conditions. The CFD simulations results were compared with experimental data under cavitation and non-cavitation conditions. A good agreement has been obtained under non-cavitation conditions for global performance parameters. After the implementation of the Rayleigh Plesset cavitation model, the required Net Positive Suction Head (NPSHr) has been predicted from CFD simulations. Finally, a full cavitation test can be reproduced for a Hydraulic Turbomachine to avoid this dangerous phenomenon.
Pipeline-risers systems are frequently encountered in the petroleum industry, especially in the offshore platforms. Single-phase flow does not involve significant troubles in the operations through these arrangements. However, during multiphase flow, flooding of the separation facilities could be expected due to the generation of severe slugs at the bottom of the riser. The size and frequency of the slugs are functions of the accumulation and displacement of liquid at the base of the riser and can be controlled with an adequate model. An improved transient model is presented to simulate severe slugging phenomenon in pipeline-risers systems. Gas penetration is described thoroughly since the first bubble penetrates into the riser until it reaches the top of it. The model presents improvements in the characteristics method applications including a correction for the gas density deviation caused by the nonfixed space-time resolution during the gas penetration. The results were compared with experimental data and previous models showing better accuracy. The model can be used to design new pipeline riser-systems or to adjust the operation of existing systems to prevent the occurrence of severe slug flow.
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