The paper refers to the numerical analysis of the internal flow in a hydraulic cross-flow turbine type Banki. A 3D-CFD steady state flow simulation has been performed using ANSYS CFX codes. The simulation includes nozzle, runner, shaft, and casing. The turbine has a specific speed of 63 (metric units), an outside runner diameter of 294 mm. Simulations were carried out using a water-air free surface model and k-εturbulence model. The objectives of this study were to analyze the velocity and pressure fields of the cross-flow within the runner and to characterize its performance for different runner speeds. Absolute flow velocity angles are obtained at runner entrance for simulations with and without the runner. Flow recirculation in the runner interblade passages and shocks of the internal cross-flow cause considerable hydraulic losses by which the efficiency of the turbine decreases significantly. The CFD simulations results were compared with experimental data and were consistent with global performance parameters.

No abstract

Two-phase flow is an area of primary interest, particularly for the petroleum industry, where a fair amount of these kinds of flows can be found in the production of oil wells. This study refers to the evaluation of two-phase flow airwater through a horizontal pipe of 0.0508m (2in) diameter and 1.016m (40in) length. A 3D CFD approach was used for reproducing the behavior of the dispersed bubble, stratified smooth and slug flow in a horizontal pipe. The pressure drop and liquid holdup associated with it were estimated. Data of the superficial velocities of the liquid and gas were taken from the literature; and then many CFD simulations were carried out using different multiphase flow models. The results were validated with the available experimental data from the literature. For the case in which the liquid is the continuous phase and the gas behaves as the dispersed one, the results show that the bubble disperse flow behaves homogeneously. In these simulations, for a 0.01mm gas bubble diameter the pressure drop presented a deviation of 6.12% over that reported in the literature. For the liquid holdup value a difference of 0.001% was obtained. An inhomogeneous approach with the free surface model reproduced satisfactorily the stratified smooth behavior. In addition, the influences of increasing water superficial velocity on the energy losses and the liquid holdup were obtained. However, for the studied numerical domain, the slug flow pattern could not be reproduced. All these results above allowed us to establish the great applicability of CFD modeling in the problem resolution of two-phase flow in a horizontal pipe.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractA geomechanical study for naturally fractured carbonates was performed as part of an integrated study for the Mara Oeste field in Venezuela. The study included working with one paleomagnetically-oriented core in which natural and induced fractures were identified and oriented. Geomechanical static and dynamic laboratory tests were performed, to obtain strength, deformability and failure characteristics of the rocks. The in situ stress field orientation was determined in one well by using special core techniques such as ASR, DSA, AAA and SWAA. Regional information provided by focal mechanism data available in the Maracaibo basin was integrated together with image logs for eleven wells. Natural fractures and breakouts were studied and fracture orientation and in situ stresses were related with geological structures present in the field. A stress orientation map was built with all the available directional information. In situ stress magnitude was estimated by lost-circulation data, extended leakoff test and backanalysis from breakouts. A three-dimensional stress model of the field was performed using a lagrangian finite difference code. The model showed that stress orientation is dependent on geometry of the layers, and faulting can introduce jumps in stress magnitude. Out from the influence of the main faults the model reproduced the regional trend of stresses. Close to the main fault of Mara Oeste, stress rotation was evident both in depth and spatially, particularly at the crest of the folds. The model provided estimates of in situ stress magnitude that can be used to design new wells in blocks with little information.

No abstract