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In this paper, we present a reliable micro-to-macroscale framework to model multiphase fluid flow through fractured porous media. This is based on utilizing the capabilities of the lattice Boltzmann method (LBM) within the phase-field modeling (PFM) of fractures in multiphase porous media. In this, we propose new physically motivated phase-field-dependent relationships for the residual saturation, the intrinsic as well as relative permeabilities. In addition, an anisotropic, phase-field-dependent intrinsic permeability tensor for the fractured porous domains is formulated, which relies on the single-and multiphasic LBM flow simulations. Based on these results, new relationships for the variation of the macroscopic theory of porous media (TPM)-PFM model parameters in the transition zone are proposed. Whereby, a multiscale concept for the coupling between the multiphasic flow through the crack on one hand and the porous ambient, on the other hand, is achieved. The hybrid model is numerically applied on a real microgeometry of fractured porous media, extracted via X-ray microcomputed tomography data of fractured Berea Sandstone. Moreover, the model is utilized for the calculation of the fluid leak-off from the crack to the intact zones. Additionally, the effects of the depth of the transition zone and the orientation of the crack channels on the amount of leakage flow rates are studied. The outcomes of the numerical model proved the reliability of the multiscale model to simulate multiphasic fluid flow through fractured porous media.

In this contribution, the Shan-Chen (SC) two-phase flow model of the lattice Boltzmann method (LBM) is numerically implemented to simulate multiphase fluid flow on microtomography (µ-CT) data of a sphere packing. From the model, the saturation degrees of the fluid phases, i.e. invading and displaced fluids, are extracted from the computed lattice density distribution functions. Several simulations are run with different degrees of kinetic viscosity contrast between the fluid phases within increasing increments of capillary pressure. At each increment, the relative permeability regarding each fluid phase is computed as a function of the saturation degree. The motivation of this study is to (1) investigate the effect of the kinetic viscosity contrast between the fluid phases on the retention behavior, (2) analyze the range of validity of the van Genuchten relation according to the computed retention data and (3) propose an extension towards an upscaling micro-to-macroscopic hierarchic scheme for the simulation of multiphasic fluid flow in unsaturated porous media.

The influence of generator load changes on partial discharge (PD) activity can be significant especially when the semi-conductive coating of stator bars is eroded. It is common knowledge that thermal expansion (copper, core and insulation) wiD decrease the gap size in the slot between the bar and the core and this could lead to a reduction of slot PD activity. In the present study, a surface defect was made on a stator bar and a variable gap between the bare insulation surface and a ground plane was adjusted from close contact to fixed gaps of 0.25, 0.5 and 1.0 mm. Partial discharge measurements were recorded at different temperatures for each of these four gap sizes. The stator bar was both electricaOy stressed at 8.0 kV and thermally stressed by a circulating current. For each gap dimension, PD tests were carried out at room temperature (22°C), and with circulating current at 53, 70, 90 and 132°C. By comparing results from different gaps at a fixed temperature and results from different temperatures at a fixed gap, it was possible to determine which one of these two parameters had the greatest influence on the PD signals. The effect of these changes with respect to gap size was compared with an evaluation of the thermal expansion of a bar in its slot under normal operating conditions. This study leads to a better understanding of the change expected in slot PD activity with load variations when measurements will be performed on actual generators. l INTRODUCTIONOn-line partial discharge signals can show significant variation in pulse amplitudes and numbers depending on the load condition of a generator. Generally, this PD activity will remain fairly constant for generators in good condition and yearly measurement will be similar with only slow changes associated with the normal degradation by internal PD of the insulation system. However, when specific problems are present, such as slot discharges or degradation of the stress grading coating, the detected PD activity from one year to the next could change significantly due to degradation, but also due to variation in environmental/operating conditions.The intent of the CUtTent study is to evaluate the contribution oftwo of the main parameters affecting slot discharge activity: temperature and gap size. Bar vibration, which is another key factor influencing slot PD intensity, is not covered in this paper. As the load of a generator increases, the thermal expansion of the copper and the insulation could partially fill the gap between the bare insulation surface and the grOWlded stator core lamination, also in expansion. The extent of this expansion is obviously dependant on the nature of the insulation system. It is believed that the reduction of gap should reduce slot PD activity. Even if this phenomenon is straightforward and generally accepted, there is very little documentation comparing the specific contribution of the temperature and the gap size on the detected slot PD activity. The experiment presented herein will show which one of these two parameters is ...

The following proceeding presents a multiscale approach to investigate the hydraulic anisotropy and retention behavior in porous materials involving deformation effects. Concerning the former, single-phasic fluid flow simulations using the lattice Boltzmann method (LBM) are initially accomplished at the pore-level geometry of Bentheimer sandstones provided by X-ray microscopy at several degrees of compression to compute the intrinsic permeability. Due to the anisotropic nature of the Bentheimer sandstones, favored pore channels for fluid flow are witnessed within the domain. Therefore, it is important to understand the alteration of the preferred flow paths at each degree of compression. In this regard, we propose a new upscaling approach between the LBM and the macroscopic Theory of Porous Media (TPM) to accurately compute the macroscopic hydraulic structural tensor, which plays a crucial role in the calculation of the deformation-dependent anisotropic specific permeability. As for the latter, the Shan-Chen (SC) model of the LBM is applied at each strain level to model biphasic fluid flow via the unsaturated porous domain. Herein, the retention curves of the drainage and imbibition processes of each deformed state are computed. In turn, the comparison among the results shows the effect of variation of the strain degree on the retention behavior.