Two-dimensional Numerical Simulations Research Articles

Coupling mechanisms of displacement and imbibition in pore-fracture system of tight oil reservoir

Fracturing and water flooding have been popular technologies to achieve the effective development of tight oil reservoirs in recent years. However, in the late stage of production, the oil recovery rate declines with a rapid increase in the water cut. Water huff-puff could improve reservoir energy; however, the displacement and imbibition in the micro-nano pore throat and fracture systems are complex processes with unclear characteristics and position. Therefore, it is urgent to study the coupling mechanisms of oil-water displacement and imbibition in tight oil reservoirs. In this work, based on the phase field method of COMSOL Multiphysics software, we establish a two-dimensional microscopic numerical simulation model of the pore-fracture system, and carry out displacement-imbibition simulation programs of different injection media (water and surfactant) and injection methods (displacement, displacement-imbibition). By comparing the saturations and pressure distributions of different simulation programs, we analyze the changes in the oil-water interface, and summarize the action conditions of counter-current imbibition and pore throat limit. Finally, reasonable development suggestions are proposed for tight oil reservoirs. Cited as: Pi, Z., Peng, H., Jia, Z., Zhou, J, Cao, R. Coupling mechanisms of displacement and imbibition in pore-fracture system of tight oil reservoir. Capillarity, 2023, 7(1): 13-24. https://doi.org/10.46690/capi.2023.04.02

Theoretical and numerical studies on dissolution of horizontal salt body and pattern formation incorporated with a dynamic moving interface

The dissolution of a horizontal salt body is theoretically and numerically investigated by considering the coupled dynamics of the dissolution reaction and the diffusive and convective mass transfer at the salt surface. To take into account the nature of the recessing salt surface and the dissolution-driven convection, a dynamic moving boundary condition coupled with a dissolution reaction are employed By employing a newly derived moving interface condition and parameters, a theoretical analysis predicts the onset of gravitational instability, suggesting scaling relationships between parameters to describe the onset of instability (in transport-dominant (Damkholer number $Da \to \infty $ and Rayleigh number $Ra > {10^5}$ ), onset time ${\tau _d}\sim R{a^{ - 2/3}}$ and ${\tau _d}\sim (RaDa)^{1/4}$ for reaction-dominant regimes $(Da \to 0)$ ). The scaling relationships on dissolution (the average height change, $\Delta {h_{avg}}\sim \sqrt \tau $ for the diffusion-dominant regime and $\Delta {h_{avg}}\sim R{a^{0.79/3}}{\tau ^{0.86}}$ for the convection-dominant regime) are also suggested to explain the pattern formation. Under a convective mass transfer condition, the concentration gradient of the solute developed during the recession of the salt surface results in an adverse density gradient, which causes gravitational instability motion and finally determines the formation of a dissolution pattern. In addition, two-dimensional and three-dimensional numerical simulations visualize dissolution-driven convective flow fields, the recession of the liquid-solid interface and pattern formation on the dissolving interface. Theoretical and numerical analyses of the dissolution process suggest that the control of gravitational instability is important to prevent or enhance dissolution pattern formation. This systematic parameter study provides a deep understanding of the effect of gravitational instability on convection-driven dissolution in a horizontal geometry.

Coupling characteristic analysis and propagation direction control in hydrogen–air rotating detonation combustor with turbine

Two-dimensional numerical simulations are performed to investigate the interactions between a rotating detonation combustor (RDC) and turbine. The flowfield structure and coupling characteristics are analyzed under different equivalent ratios. Furthermore, the formation mechanism of the detonation wave direction is illustrated. Results show that although RDCs increase the average turbine work, they enhance the flowfield oscillation and maintain the quasi-periodic fluctuation in the turbine work. Compared to counter-clockwise propagation, the pressure oscillation attenuation and total pressure loss through the turbine guide vane increase when the detonation wave propagates clockwise. When the detonation wave height is low, RDCs are more prone to quenching due to the impact of reflected waves. After re-ignition, the detonation wave direction is unrelated to the initial ignition direction and is random. Introduction of deflecting wedges into RDCs enables the automatic control of the detonation wave direction but causes extra total pressure loss of at least 3.6%.

Improvement of single event effects in InP-based HEMT with a composite channel of InGaAs/InAs/InGaAs

In this paper, a hardened single event effects in InP-based HEMT with a InGaAs/InAs/InGaAs composite channel (CC HEMT) is investigated by the two-dimensional numerical simulations. The composite channel significantly improves the single event effects. Compared to the conventional InP-based HEMT with single InGaAs channel (SC HEMT), the peak drain current is markedly decreased for CC HEMT, owing to a high barrier in the InGaAs/InAs/InGaAs locates electrons in the middle of the sandwiched layer. In addition, the electron concentration of the InAs channel is smaller of CC HEMT than that of InGaAs channel of SC HEMT after ion strike. This also makes the decrease in drain current. Through optimal device parameters, the peak drain current of the CC HEMT with 9/1/5 nm In0.8Ga0.2As/InAs/In0.8Ga0.2 channel is 129.1 % smaller than that of the SC HEMT with In0.53Ga0.47 channel.

Numerical investigation of the effect of hot-water outlet inclination angle on the temperature dilution in open channel flow

In this study, the authors investigated the environmental impact of discharging hot water from a thermal power plant into a water source for cooling. Three hundred forty-three runs using two-dimensional numerical ANSYS Fluent simulation model with (k- ε) turbulence model and open channel flow characteristics was applied in this research. The single port submerged discharge inclination angle was studied with different scenarios for the hot-water outlet (velocity and temperature) to determine the optimum inclination angle to increase cooling system efficiency and reduce hot water's environmental impact. It was discovered that by increasing the inclination angle and velocity of the hot-water outlet, the efficiency of cooling system is increased, as it increased the dilution of the hot water and reduced its environmental impact. Specifically, inclination angle of 15° increased the dilution by 80% and 86% in x and y directions, respectively compared to angle 90°. Additionally, the temperature variation in water body induced by hot-water outlet was reduced by counter flow at angle −15°. The velocity profile showed a recirculation region at the right side of the hot-water outlet, which was reduced at higher inclinations. A mathematical equation was developed to estimate the temperature value in the open channel water body based on the study parameters. Overall, the study found that increasing the inclination angle of the hot-water outlet can significantly improve the cooling system's efficiency and reduce the environmental impact of the hot water discharge. Counter flow conditions were unsuitable because they have less dilution than the normal flow conditions.

Geometric Characteristics of Flapping Foils for Enhanced Propulsive Efficiency

AbstractThe shape of a foil undergoing a combined pitching heaving motion is critical to its design in applications that demand high efficiency and thrust. This study focuses on understanding of how the shape of a foil affects its propulsive performance. We perform two-dimensional numerical simulations of fluid flows around a flapping foil for different governing parameters in the range of biological swimmers and bio-inspired underwater vehicles. By varying the foil shape using a class-shape transformation method, we investigate a broad range of foil-like shapes. In the study, we also show consistent results with previous studies that a thicker leading-edge and sharper trailing-edge makes for a more efficient foil shape undergoing a flapping motion. In addition, we explain that the performance of the foil is highly sensitive to its shape, specifically the thickness of the foil between the 18th and 50th percent along the chord of the foil. Moreover, we elucidate the flow mechanisms behind variations in performance metrics, particularly focused on constructive interference between the vortices generated at the leading-edge with the trailing-edge vortex, as well as the pressure field differences that lead to higher power consumption in less efficient foil shapes.

Numerical study of viscoelastic upstream instability

In this work, we report numerical results on the flow instability and bifurcation of a viscoelastic fluid in the upstream region of a cylinder in a confined narrow channel. Two-dimensional direct numerical simulations based on the FENE-P model (the finite-extensible nonlinear elastic model with the Peterlin closure) are conducted with numerical stabilization techniques. Our results show that the macroscopic viscoelastic constitutive relation can capture the viscoelastic upstream instability reported in previous experiments for low-Reynolds-number flows. The numerical simulations reveal that the non-dimensional recirculation length (LD) is affected by the cylinder blockage ratio (BR), the Weissenberg number (Wi), the viscosity ratio (β) and the maximum polymer extension (L). Close to the onset of upstream recirculation, LD with Wi satisfy Landau-type quartic potential under certain parameter space. The bifurcation may exhibit subcritical behaviour depending on the values of L2 and β. The parameters β and L2 have nonlinear influence on the upstream recirculation length. This work contributes to our theoretical understanding of this new instability mechanism in viscoelastic wake flows.

Numerical Simulation Study on the Influence of Construction Load on the Cutoff Wall in Reservoir Engineering

Relying on the Beijing-Shijiazhuang Expressway widening project near the impervious wall of a reservoir, this paper uses FLAC3D two-dimensional and three-dimensional numerical simulation methods to establish the whole process model of the impervious wall of the reservoir affected by the construction load of the high-way reconstruction section. The stress and strain state of the cut-off wall in the high-way reconstruction section and the nearby reservoir is simulated in detail, the overall deformation of the cut-off wall in the reservoir is directly reflected, and the interaction and differential deformation between the wall structures are reflected. The safety and stability of the cutoff wall of the reservoir affected by the construction load are evaluated so that various advanced mechanical behaviors of the cutoff wall can be predicted. Research results show that the horizontal displacement value of the wall gradually increases from bottom to top, and the maximum value appears at the top of the wall. The horizontal displacement value of the 1–3 walls is relatively large, with the maximum value of 22.368 mm, and the horizontal displacement value of the 4–10 walls shows little difference. This is on account of the gravity of the backfill, the strata in the whole project area having settled, and the settlement at the bottom of the cut-off wall being 2.542 mm. At the root of the rigid cut-off wall, the compressive stress concentration occurs, with the maximum value between 1.75 MPa and 2.15 MPa. Due to the size of the structure, the maximum tensile stress of 0.237 MPa appears in the local area near the guide wall of the rigid cut-off wall, which will not endanger the rigid cut-off wall because of its small value. The maximum stress in the rigid impervious wall and the plastic impervious wall are 1.90–2.15 MPa and 1.00–1.12 MPa, respectively. Apart from the small tensile stress at the connecting guide wall between the rigid cut-off wall and the plastic concrete cut-off wall, the cut-off wall is under pressure, especially the plastic cut-off wall. Combined with the analysis of the stress state of the wall, it can be determined that the anti-seepage wall (rigid cut-off wall and plastic concrete cut-off wall) is stable and safe during the construction period.

Reduction of fluid forces for flow past side-by-side cylinders using downstream attached splitter plates.

A two-dimensional numerical simulation is performed to investigate the drag reduction and vortex shedding suppression behind three square cylinders with attached splitter plates in the downstream region at a low Reynolds number (Re = 150). Numerical calculations are carried out using the lattice Boltzmann method. The study is carried out for various values of gap spacing between the cylinders and different splitter plate lengths. The vortices are completely chaotic at very small spacing, as observed. The splitter plates are critical in suppressing shedding and reducing drag on the objects. The splitter plates with lengths greater than two fully control the jet interaction at low spacing values. There is maximum percentage reduction in CDmean for small spacing and the selected largest splitter plate length. Furthermore, systematic investigation reveals that splitter plates significantly suppress the fluctuating lift in addition to drastically reducing the drag.

Design and Numerical Simulation of the Headworks in the Shizuishan Section of the Yellow River

Irrigation water for agriculture in Ningxia during the summer is primarily sourced from the Yellow River self-flow irrigation region. However, the water conveyance system in this region is significantly influenced by hydrodynamic factors, morphological factors, human factors, and the infrastructure used for social purposes, all of which directly impact the irrigation water utilization coefficient. In order to improve the irrigation water utilization coefficient, reduce suspended sediment deposition in the water conveyance channels, and mitigate negative effects on the water supply system, this study implemented a sediment diversion system at the channel head. This is expected to increase water usage efficiency to a certain degree. Using actual data on hydrodynamic factors from the Shizuishan section of the Yellow River in Ningxia, a two-dimensional numerical simulation was performed, and a two-dimensional hydrodynamic model and sediment model of the Shizuishan section of the Yellow River in Ningxia were developed using MIKE 21. The water conveyance method at the channel head was simulated under two different operating conditions. Results indicated that compared to operating condition 1, operating condition 2 had a beneficial effect on diverting and reducing sediment at the fish mouth of the channel head: the sediment accumulation thickness of one day in operating condition 1 was 0.16 m, 0.003 m, 0.15 m, and 0.21 m under actual flow, scenario 1, scenario 2, and scenario 3, respectively; whereas in operating condition 2, the sediment accumulation thickness of one day was 0.11 m, 0.001 m, 0.09 m, and 0.12 m under the same conditions, respectively. Additionally, as the computation period lengthened, the sediment accumulation thickness of operating condition 2 was significantly smaller than that of operating condition 1. In conclusion, operating condition 2 is superior for the design of the channel head in the Yellow River self-flow irrigation region.

Heat transfer characteristics of double pipe heat exchanger having externally enhanced inner pipe

An investigation on enhancement of heat transfer is carried out for a double pipe heat exchanger in which the outer wall of the inner pipe is provided with circumferential labyrinth passages. Rectangular and triangular cavities with fixed labyrinth tooth thickness, height, and pitch are considered and the effect of added labyrinth structures on the heat transfer characteristics is discussed. A two-dimensional steady numerical simulation is carried out using ANSYS-FLUENT software. The flow Reynolds number equals to 20 000 and 43 000 for the hot and cold fluids, respectively, while other fluid properties are constant. From the numerical analysis carried out in this work, it is identified that the added labyrinth passages in the heat exchange surface improve the heat transfer rate and can reduce the length of the heat exchanger. Numerical predictions agree well with the results obtained from the experiment conducted.

Numerical simulation the fracture of rock in the framework of plastic-bond-based SPH and its applications

In this paper, a two-dimensional numerical approach named plastic-bond-based smoothed particle hydrodynamics (PB-SPH) is proposed to simulate the fracture of rock with pre-existing flaws. Under the PB-SPH framework, interaction particles are interconnected through bonds. The Drucker–Prager criterion of a tensile zone cut-off coupled maximum tensile stress criterion is applied to judge shear failure and tensile failure. To verify the capability of the PB-SPH method in simulating rock fracture behavior, two-dimensional numerical simulations of a single flaw, two coplanar flaws, and multiple flaws of uniaxial compression are carried out. Compared with previous experimental and numerical results, the present numerical results show good agreements on crack initiation positions, crack morphology and crack patterns. The numerical simulation of the progressive failure process of rock slope with multiple flaws is carried out, which shows that the PB-SPH method can be well applied to rock mechanics engineering. The present results show that the PB-SPH method has a certain reference in the study of rock fracture mechanics and the application of rock mechanics engineering.

Heat transfer modulation in Rayleigh–Bénard convection by an oscillatory bottom plate

In this paper, we consider a heat transfer modulation in Rayleigh–Bénard convection by imposing a periodic sinusoidal oscillation to the bottom hot plate parallel to itself. Two-dimensional numerical simulations are carried out under lateral periodic conditions, over a Rayleigh number range of 106≤Ra≤109 and for a fixed Prandtl number of Pr = 7.1. For a given Rayleigh number, it is found that the Nusselt number, characterizing the global heat transfer efficiency of the system, shows a counter-intuitive initial drop and subsequent rise behavior, as the characteristic oscillatory velocity Vosc increases. Accordingly, taking the classical Rayleigh–Bénard convection as a reference, a heat transfer reduction regime for low Vosc and a heat transfer enhancement regime for high Vosc are recognized. The reduction regime is resulted from the thickening of the thermal boundary layer due to the amplified viscous effect by the oscillation, which increases the thermal resistance of the system. In addition to thickening the thermal boundary layer, a stronger oscillation could also trigger a thermal boundary layer instability, inducing massive emission of the thermal plumes and eventually giving rise to a significant global heat transfer enhancement. Moreover, the combined effect of thickening and destabilizing of the thermal boundary layer leads to a temporal periodic evolution of the Nusselt number at the bottom plate in the enhancement regime. A critical oscillatory velocity Vc is selected at the crossover between two regimes, and it is found decreasing with an increasing Ra as Vc∼Ra−0.2. Through dimensional analysis, we provide a physical explanation for this dependence.

Numerical Simulation of Particle Filtration by Rectangular Fibres within a Parallel and Staggered Array

In this research, two-dimensional numerical simulation is used to examine the filtration performance of rectangular fiber filters. Ansys Fluent is employed to obtain the stable flow field distribution and the DPM model is used to calculate the particle trajectories in the flow field. The effect of pertinent factors such as fiber arrangement, particle-to-fiber diameter ratio, and Stokes number on the performance of rectangular fiber filters are analyzed. The simulation results indicate that both the parallel and staggered arrays of rectangular fibers have a significant influence on the capture efficiency and pressure drop. At the same flow velocity, the pressure drop of the fibers with a parallel array is lower than that of the staggered array fiber model. The capture efficiency of the staggered array model and the parallel array model increases with the increase of the ratio of particle to fiber diameter and the Stokes number. When the interception and inertial impaction mechanisms domiant, the filter with a staggered fiber array structure performs batter than the parallel array in terms of capture efficiency. The research results can provide a theoretical basis for the structure optimization and design of the air filter with multi-layer fiber.

Modelling and analysis of vortex induced vibration in marine risers

Marine Risers that are used to extract crude oil from the seabed to offshore platforms are subjected to Vortex-Induced Vibrations (VIV) in interaction with the external fluid flow of seawater. The study of VIV is essential as it plays a crucial role in designing marine risers. This paper focuses on creating a two-dimensional numerical simulation of a circular cylinder of Marine Riser which is exposed to different current velocities to estimate parameters such as Lift coefficient, Drag Coefficient, and Shedding frequency of VIV. The shedding frequencies obtained from the numerical model are compared with the natural frequencies of the riser to get the lock-in condition of the riser which ultimately gives rise to VIV. In addition to this, an analytical model is developed to find out the natural frequencies of the risers. Hence the vortex-induced vibrations in the lock-in region can be reduced by increasing the tension which should be within the maximum over pull.

Cooling performance of an active-passive hybrid composite phase change material (HcPCM) finned heat sink: Constant operating mode

The present study explores a hybrid thermal management technology based on air cooling and hybrid composite phase change material (HcPCM) filled finned heat sink for cooling performance of lower to medium heat flux dissipating electronic devices. Two-dimensional numerical simulations are conducted to study the conjugate heat transfer effects of three types of finned heat sink: air-cooled finned heat sink, HcPCM-cooled finned heat sink, and hybrid (air-HcPCM) cooled finned heat sink. A heat sink with a constant volume faction of plate-fins is designed in all cases and simultaneous effects of hybrid nanoparticles and air are investigated to keep the heat sink temperature at safe operating conditions between 40–60 ∘C. The effect of air is incorporated into the heat sink by applying the convective heat transfer coefficient of hc = 10–100 W/m2.K which tends to create the natural convection and forced convection heat transfer characteristics. The heat flux is varied from 25–40 kW/m2 in the current study. The hybrid nanoparticles of carbon additives (GO and MWCNTs) are dispersed into the RT-35HC, used as a PCM, with a volume fraction of 0% to 6%. Transient simulations are carried out using COMSOL Multiphysics to solve the governing equations for PCM based conjugate heat transfer model. The results showed that forced convection heat transfer improved the cooling performance of the hybrid heat sink compared to natural convection heat transfer. The addition of nanoparticles further enhanced thermal enhancement and uniform melting distribution of PCM inside the finned heat sink. The hc between 30 to 50 W/m2.K shows optimized values for forced convection heat transfer operating conditions. The volume fraction of 2% of GO+MWCNTs nanoparticles in recommended or optimum concentration for uniform melting of PCM inside the finned heat sink.

Effect of Gap Length and Partition Thickness on Thermal Boundary Layer in Thermal Convection

Two-dimensional direct numerical simulations of partitioned thermal convection are performed using the thermal lattice Boltzmann method for the Rayleigh number (Ra) of 109 and the Prandtl number (Pr) of 7.02 (water). The influence of the partition walls on the thermal boundary layer is mainly focused on. Moreover, to better describe the spatially nonuniform thermal boundary layer, the definition of the thermal boundary layer is extended. The numerical simulation results show that the gap length significantly affects the thermal boundary layer and Nusselt number (Nu). The gap length and partition wall thickness have a coupled effect on the thermal boundary layer and the heat flux. Based on the shape of the thermal boundary layer distribution, two different heat transfer models are identified at different gap lengths. This study provides a basis for improving the understanding of the effect of partitions on the thermal boundary layer in thermal convection.

Enhanced delivery of remedial reagents in low-permeability aquifers through coupling with groundwater circulation well

Limited dispersion and mass transfer because of hydrogeological heterogeneity make it difficult to deliver remedial reagents to desired locations. Remediation alternatives that overcome mass transfer limitations are required urgently to improve the efficiency of in situ remediation techniques. In this study, a combination of two-dimensional sandbox experiments and numerical simulations was used to explore the migration process of remedial reagents driven by groundwater circulating well (GCW). The influences of the circulating flow rate, concentration of the remedial reagent (H2O2 as a model) and cycle operation mode on the migration of GCW enhanced remedial reagents were investigated. The flow rate of the pumped water can enhance the concentration gradient at the interface of different permeation zones. The redistribution of reagents by increased Fick diffusion significantly increased the dispersion range. The results of parametric sensitivity analysis showed that the aggregation effect of remedial reagents in the low permeability area (∼10-7 m/s) and related to the injection site. Considering remedial reagents attenuation, a reactive transport model can better simulate the concentration changes in low-permeability regions (R2 > 0.960). The numerical simulation results showed that the principal component of the hydrodynamic field was tangential to the main axis of the target area. The diffusion coefficient of the low-permeability region was one order of magnitude lower than that of the high-permeability region (∼10-3 m/s). Thus, the low-permeability region was less affected by the hydraulic action of the GCW and had a longer retention time for remedial reagents. Specific aquifer parameters and operating modes are key engineering design factors of a GCW that should be considered in conjunction with other in situ chemical technologies. This study provides some new insights for in situ remediation of contanminated aquifers with a GCW, and suggests that (i) the hydraulic circulation driven by GCW can promote the accumulation of injected remedial agents in low permeability areas, especially injection point is located near wellbore; and (ii) residence time of reagents in contaminated areas should be comprehensively considered when chemical remediation technology is coupled with GCW. The results of this study can be used to improve the delivery efficiency of remedial reagents in contaminated aquifers.

Inclination and heterogeneity of layered geological sequences influence dike-induced ground deformation

Abstract Constraints on the amount and pattern of ground deformation induced by dike emplacement are important for assessing potential eruptions. The vast majority of ground deformation inversions made for volcano monitoring during volcanic unrest assume that dikes are emplaced in either an elastic half-space (a homogeneous crust) or a crust made of horizontal layers with different mechanical properties. We extend these models by designing a novel set of two-dimensional finite-element method numerical simulations that consider dike-induced surface deformation related to a mechanically heterogeneous crust with inclined layers, thus modeling a common geometry in stratovolcanoes and crustal segments that have been folded by tectonic forces. Our results confirm that layer inclination can produce localized ground deformation that may be as much as 40× higher in terms of deformation magnitude than would be expected in a non-layered model, depending on the angle of inclination and the stiffness of the rock units that host and are adjacent to the dike. Generated asymmetrical deformation patterns produce deformation peaks located as much as 1.4 km away from those expected in non-layered models. These results highlight the necessity of accurately quantifying both the mechanical properties and attitude of the geology underlying active volcanoes.

The impact on mc-Si ingot grown in a directional solidification furnace by partially replacing the susceptor bottom with an insulation material: A numerical investigation

Directional solidification (DS) is the major process for growing the multi-crystalline silicon (mc-Si) ingots with low cost and low power consumption. Here, the investigation of mc-Si growth has been carried out by two-dimensional numerical simulations on the simplified axisymmetric DS furnace. The mc-Si ingots were grown in the DS furnace with conventional susceptor and a furnace with partially replaced susceptor bottom. The susceptor bottom of size 278 mm × 42 mm × 20 mm is partially replaced with an insulation material. The temperature distribution and melt-crystal interface shape of the grown ingots were analysed at 25%, 50% and 75% of the solidification fraction. The von Mises stress and max shear stress were investigated on both the ingots at the end of the DS-Si process. The better quality mc-Si ingot with low power consumption has been attained by the partial replacement of susceptor bottom with insulation block.