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Mesh generation lies at the interface of geological modeling and reservoir simulation. Highly skewed or very small grid cells may be necessary to accurately capture the geometry of geological features, but the resulting poorly scaled or small grid cells can have a substantial negative impact on simulator accuracy and speed. One way to minimize numerical errors caused by gridding complex structures is to simulate on high-quality Voronoi meshes, which reduce grid orientation effects in fluid flow. This work presents a complete methodology to create Voronoi simulation grids, model fluid flow in complex geological systems, and visualize the results. A recently developed Voronoi meshing method that can automatically generate provably good unstructured meshes that conform to input surfaces creating closed volumes is used. Initially an analytical benchmark simulation is presented to validate the quality of the meshes and simulation results and demonstrate the superiority of simulation results using Voronoi meshes over flexed-hexahedral meshes on a domain with internal features. Next, meshes are created for test structures representing four of the most common geological features in the subsurface: layering, pinch-out, an interior lens that tapers to zero thickness on all sides and a fault with offset. Two benchmark flow simulations are run for each test structure. Finally, a realistic geological example for CO$$_2$$ 2 injection into an anticline is simulated. Three realizations of the Voronoi mesh at the same resolution are generated for the simulations. Each mesh is highly refined near the injection wells and coarse in areas of less interest. These three meshes are used to model the CO$$_2$$ 2 plume in the subsurface as it migrates to the top of the structure and then fills downward. Simulations on the meshes with randomly generated elements inside the input volumes each give slightly different fingering patterns for the viscous-unstable buoyant gas flow. The results presented in this work show a promising step towards utilizing fully automated Voronoi meshing for subsurface flow simulations in complex geology.

In a geological CO2 storage site, the main migration pathways in case of leakage would be compromised boreholes or gas permeable faults or fractures. In this work we propose a modeling workflow based on detailed field data acquired on a fault exposed in the Roman Valley Quarry (Majella Mountain, Italy), to simulate the three-dimensional migration of gas CO2 in the fault zone. The numerical modeling is performed using the open-source multiphase flow simulator PFLOTRAN. This study provides a new methodology to characterize the hydraulic behavior of a fault including all its components, the core and the damage zone, capturing in detail the impact of the fault zone architecture to the migration of CO2. Simulation test results point out the robustness of the modeling approach, highlighting its strong predictive power, and show how most of the gas migrates through the high permeable footwall damage zone, where the injection occurs, whereas some of the gas also migrates through the hanging wall damage zone and the fault core. The buildup of gas pressure in the vicinity of the injection wells demonstrates the need of increasingly accurate modeling of the injection conditions to avoid possible faults reactivation and CO2 leakage. While the technique presented here is applied to a case scenario on carbonate rocks, the proposed methodology can be extended to other geological scenarios, by the appropriate calibration of the geometric and petrophysical parameters of fractures and host rock, to understand the conditions under which faults can promote fluid flow from a reservoir and mitigate the risk of CO2 migration via faults.

Double-perforated liners are widely used in gas turbine combustors because of their improved thermal load characteristics and broader acoustic damping compared with single-layer perforations. The present study examines the absorption of normal-incidence acoustic waves by double perforated liner, and provides quantitative analysis results on the effects of key liner parameters on the acoustic damping characteristics using the electro-acoustic analogy method. The developed impedance model is successfully validated against the measured data in the literature. Then, the impedance model is applied to the design of a double-perforated liner in the aero-engine combustor under development and the optimal liner design results are shown in terms of acoustic damping. It is found that the dome plate porosity and the plate gap, which is the space between the dome and splash plate, have a major impact on acoustic absorption for a given combustor geometry and flow condition. In contrasts, the splash porosity and plate thickness have minor significance over frequency range of interest. Thus, the optimized liner configurations are proposed from the viewpoint of acoustic damping.

The side-wall cooling liner in a gas turbine combustor serves main purposes—heat transfer and emission control. Additionally, it functions as a passive damper to attenuate thermoacoustic instabilities. The perforations in the liner mainly convert acoustic energy into kinetic energy through vortex shedding at the orifice rims. In the previous decades, several analytical and semi-empirical models have been proposed to predict the acoustic damping of the perforated liner. In the current study, a few of the models are considered to embody the transfer matrix method (TMM) for analyzing the acoustic dissipation in a concentric tube resonator with a perforated element and validated against experimental data in the literature. All models are shown to quantitatively appropriately predict the acoustic behavior under high bias flow velocity conditions. Then, the models are applied to maximize the damping performance in a realistic gas turbine combustor, which is under development. It is found that the ratio of the bias flow Mach number to the porosity can be used as a design guideline in choosing the optimal combination of the number and diameter of perforations in terms of acoustic damping.