Publication date: 30 January 2026

Source: Computers & Fluids, Volume 305

Author(s): Linqi Yu, Yanyun Chen, Mustafa Z. Yousif, Hee-Chang Lim

Publication date: 30 January 2026

Source: Computers & Fluids, Volume 305

Author(s): Junzhe Cao, Yufeng Wei, Wenpei Long, Chengwen Zhong, Kun Xu

Publication date: 30 January 2026

Source: Computers & Fluids, Volume 305

Author(s): Mirco Ciallella, Julian Koellermeier

Publication date: 30 January 2026

Source: Computers & Fluids, Volume 305

Author(s): Toru Yamada, Ryuga Sumi, Yohei Morinishi

Publication date: 30 January 2026

Source: Computers & Fluids, Volume 305

Author(s): Alessandro Ceci, Andrea Palumbo, Sergio Pirozzoli

Publication date: 30 January 2026

Source: Computers & Fluids, Volume 305

Author(s): Seiya Watanabe, Hiroaki Kuranaga, Changhong Hu

Publication date: 30 January 2026

Source: Computers & Fluids, Volume 305

Author(s): Rajat Kumar Sarkar, Vishal Jadhav, Venkataramana Runkana

Publication date: 30 January 2026

Source: Computers & Fluids, Volume 305

Author(s): Anand Srinivasan, Perry Johnson, José Castillo

Publication date: 30 January 2026

Source: Computers & Fluids, Volume 305

Author(s): Philippe Helluy, Olivier Hurisse

Publication date: 30 January 2026

Source: Computers & Fluids, Volume 305

Author(s):

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Volume 39, Issue 1, January 2025, Page 1-29
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Volume 39, Issue 1, January 2025, Page 30-50
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Volume 39, Issue 1, January 2025, Page 51-68
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By integrating the SUPG stabilization with a residual-based a posteriori error estimation, the proposed method achieves adaptive node refinement in critical regions, successfully handling magnetohydrodynamics (MHD) flow problems with very high Hartmann numbers, which far exceed other numerical methods.

ABSTRACT

This paper presents an adaptive element-free Galerkin (EFG) method with streamline upwind Petrov-Galerkin (AEFG-SUPG) stabilization for solving steady magnetohydrodynamic (MHD) flows in insulated ducts with varying cross-sections at very high Hartmann number. The governing equations are first decoupled into convection-diffusion form via variable transformations, and discretized using the EFG method with SUPG (EFG-SUPG) stabilization to deal with numerical oscillations induced by strong convection dominance. To further improve accuracy and computational efficiency, an adaptive algorithm is developed, which incorporates a posteriori error estimation based on the background integration cell residual into the EFG-SUPG framework. This adaptive strategy enables node refinement in critical regions, remarkably reducing the total number of nodes compared to traditional uniform refinement methods. Four numerical cases involving square, circular, and arbitrary duct geometries with different magnetic field orientations are analyzed for Hartmann numbers M$$ M $$ ranging from 102$$ 1{0}^2 $$ to 1018$$ 1{0}^{18} $$. The results highlight that the proposed method successfully resolves boundary layers and suppresses spurious oscillations even at M=1018$$ M=1{0}^{18} $$. Compared with existing adaptive meshless methods, it demonstrates superior computational efficiency and solution stability, showcasing its effectiveness in handling very high Hartmann number MHD flow problems in complex duct structures.

The surface-energy-based model conserves mass the best and can capture tiny features in interfacial movement. The continuum-surface-force-based model will, however, cause severe mass loss. But, by modifying the Delta-like function in the continuum-surface-force-based model, its performance in capturing tiny features can be improved.

ABSTRACT

Surface tension matters in the simulation of two-phase flow. It is formulated mostly via the continuum surface force model or the surface-energy-based model. This paper compares the performance of three surface tension models, two based on the continuum surface force model and one on the other, in the Navier–Stokes equation coupled with the conservative Allen-Cahn/phase field model. The numerical model was solved using an explicit finite difference method on a half-staggered grid. A mesh independence study was conducted to select the appropriate mesh size. The surface tension models were compared in a couple of drop impacts, including a vigorous rebound and a weak rebound. It was found that the surface-energy-based model conserves mass the best. One of the continuum surface force models can capture fine structures like capillary waves on a drop impacting a solid surface. However, the continuum surface force models suffer from much more severe mass loss. Moreover, a theoretical analysis on mass conservation was conducted, and guidance for conserving mass was proposed.

The use of simple harmonic and geometric averages for numerical solution of the Richards equation is known to lead to locked/lagged wetting fronts. By analyzing the cause of failure and inspired by the recent U-MUSCL scheme, we propose a new and cost-effective strategy to define modified non-arithmetic averages (called m-harmonic and m-geometric) that lead to accurate solutions free of numerical artifacts for both horizontal and vertical infiltration problems. Several test problems are presented to illustrate the advantages of the proposed approach, and comparisons with experimental data and/or approximate analytical solutions demonstrate the efficacy of the modified averages over the standard averages.

ABSTRACT

The one-dimensional Richards equation has been widely employed to model water flow in porous media, but the effect of averaging soil diffusivity/hydraulic conductivity on the computed solutions has received comparatively less attention than the numerical approaches to solve the equation. The use of non-arithmetic (harmonic and geometric) averaging of diffusivity in finite volume simulations of the Richards equation is known to produce numerical artifacts that include the lagging of the wetting front in time and even “locked” fronts with no flow, depending on the type of soil and the constitutive relation. In this work, we propose a new and simple approach to define the interfacial diffusivity or hydraulic conductivity based on “modified” non-arithmetic averages that mitigates the spurious artifacts at minimal computational cost. Numerical studies with unsaturated soils using different soil diffusivity models (for horizontal infiltration) and different hydraulic conductivity models (for vertical infiltration) conclusively demonstrate that the m$$ m $$-harmonic and m$$ m $$-geometric averages defined in this work lead to physically consistent solutions of the Richards equation.

ABSTRACT

Double-tube heat exchangers using ferrofluids under magnetic fields, which induce vortices, improve heat transfer and reduce irreversibilities. This study analyzes heat transfer and entropy generation of Fe₃O₄/water in a double-tube heat exchanger at Re = 100, subjected to magnetic fields. Key parameters, including inner tube cross-sectional geometry and magnetic field characteristics (intensity, wire distance, configuration, and number), are examined and optimized. The flow structure, heat transfer, friction factor coefficient, performance evaluation criterion (PEC), and entropy generation are evaluated based on thermodynamic principles. A finite volume numerical code is developed to solve the governing equations and consider the magnetic field through a UDF code on thermal and entropy performance using the SIMPLE algorithm. The investigation is evaluated: (1) the impact of the inner tube's cross-sectional geometry, (2) the effect of the current-carrying wire and outer tube distance, and (3) the influence of the magnetic field's arrangement and number. Altering the cross-sectional geometry shows that a vertically elliptical shape increases heat transfer by 81%, while the horizontally elliptical shape achieves the best overall performance. Adjusting the wire distance to d/r ₀ = 0.125 offers better overall operational performance by considering the heat transfer and entropy simultaneously. Additionally, a horizontal arrangement with two magnetic fields, which represents the optimal configuration, improves heat transfer and pressure drop by 2.8 and 21 times at Mn = 2 × 10¹⁰, and enhances the PEC by 39%. These findings can be applied in the field of energy system optimization, especially where compact design and high thermal efficiency are critical requirements.

International Journal for Numerical Methods in Fluids, Volume 98, Issue 1, January 2026.

A hierarchical multi-resolution WENO (MR-WENO) scheme is proposed in the present study to suppress the discontinuity overshoot and improve the accuracy of the original MR-WENO scheme in the vicinity of discontinuities. The present method inherits the advantages of MR-WENO and C-WENO schemes and could simultaneously guarantee convergence and high-precision characteristics. According to the 1D and 2D test cases, the hierarchical MR-WENO scheme has high accuracy in smooth regions, precise capture of discontinuities, and attenuation of overshoot due to adaptive selection of substencils.

ABSTRACT

To achieve the high-precision characteristics within the smooth regions while maintaining stable, non-oscillatory, and sharp discontinuity transitions, the weighted essentially non-oscillatory (WENO) scheme and its variants have been developed. However, when there are multiple discontinuities close to each other, the numerical accuracy and robustness of the traditional schemes are probably affected. To this end, a hierarchical multi-resolution WENO (MR-WENO) scheme is proposed in the present study to suppress the overshoot and improve the accuracy of the original MR-WENO scheme in the vicinity of discontinuities. It could achieve an adaptive selection of the substencils and optimal accuracy due to the hierarchical strategy and the new smoothness indicator. The performances of the hierarchical MR-WENO scheme have been tested in 1D and 2D cases. The accuracy has been validated and the influences of weights of both large stencils and small substencils have been comprehensively discussed. The linear weights are adjusted aiming at improving the resolution of discontinuities and suppressing the unexpected weight oscillations. As a result, discontinuities like shock waves and contact discontinuities could be accurately resolved, while overshoot phenomena in the MR-WENO scheme are effectively suppressed in both 1D and 2D cases. Especially, the numerical error of the Lax problem has been reduced by one or two orders of magnitude in the vicinity of discontinuities. With an implementation of the KXRCF indicator, the computational cost has been controlled while maintaining the present superiority of shock capturing capacity.

A novel shear-stress-based inverse design (ID) method was developed for airfoil design in the presence of a laminar separation bubble. Deep learning (DL) models were trained to correlate lift and drag coefficients with shear stress distributions (SSDs) using data generated during the ID process. The DL models were integrated into a genetic algorithm (GA) to optimize SSDs. The GA generates new SSDs to expand the search space, which are then evaluated by the DL models without requiring further ID. The optimized SSD was used in the ID process to obtain the optimal airfoil.

ABSTRACT

Pressure-based inverse design (ID) cannot converge in flow regimes with ultralow Reynolds numbers (Res). This study proposes a shear-stress-based ID method for airfoil design at Re = 1000 at the optimal angle of attack (AOA) in the presence of a laminar separation bubble. The proposed method applies the difference between the existing and target shear stress distributions (SSDs) to a deformable surface. The Navier–Stokes equations are solved to calculate the wall SSD during each iteration of the ID process. This process modifies the airfoil geometry until the abovementioned difference becomes negligible, achieving convergence to the target geometry. Achieving the maximum lift-to-drag ratio by manually correcting the wall SSD involves extensive trial and error, making it almost impossible. Thus, in the second part of this research, we trained Gaussian process regression and an ensemble of trees deep learning (DL) models using data generated during ID at the optimal AOA to predict lift and drag coefficients, respectively. The SSD was optimized throughout the ID process by coupling the DL models with a genetic algorithm (GA). Optimization was performed in several consecutive cycles, with the DL models becoming more accurate and updated as more data were gathered, helping the GA obtain the optimal SSD and geometry precisely. Finally, the performance curves of different geometries obtained through the optimization cycles were evaluated and compared using the Fluent solver. The results demonstrated a 22.42% increase in the lift-to-drag ratio relative to the initial population at the optimal AOA.

This paper presents the optimal feedback force locations in measurement-integrated simulation (MIS) for flow around a circular cylinder. The feedback force applied at an angle of 120° from the stagnation point gave the closest result to the numerical experiment. The result of this study suggested that applying the feedback force at the separation point is effective for reproducing the flow behind the object.

ABSTRACT

Measurement-integrated simulation, one of the data assimilation methods, is a simulation technique that reproduces an actual flow field by adding feedback forces, including measurement data, to the external force term of the Navier–Stokes equations. The analysis in the previous studies using wind tunnels was limited to flows around a square cylinder. There is no principle for determining the optimal location of the feedback force, and the optimal location of feedback forces for other shapes is unknown. This study aimed to identify the optimal location for applying the feedback force in the flow around a circular cylinder and explore its relationship with the flow field. Using pressure on the cylinder surface obtained from a numerical experiment with disturbed inflow containing random fluctuations as measurement data, several measurement-integrated simulations were conducted, each with a different feedback location. By comparing the results of the measurement-integrated simulation with those of the numerical experiment, the optimal position was identified at 120° from the stagnation point that most accurately reproduced the flow behind the cylinder in the numerical experiment. Furthermore, this location was identified as the flow separation point, suggesting that applying a feedback force at the separation point is optimal for reproducing the flow behind the object.

A hybrid RANS-LES turbulence model adapted for the Moving Particle Semi-implicit method is employed to investigate a turbulent free surface flow. A method based on the cell-linked list is proposed to speed up the nearest wall search for the turbulence model. Validation using lid-driven flow showed better convergence and improvements achieved by the turbulence model. The flows around a square cylinder near the surface with a Reynolds number of 25,000 were simulated and the influence of the cylinder submergence depths was investigated.

ABSTRACT

Engineering problems often comprise free-surface flows in turbulent regime. Lagrangian mesh-free particle-based methods are well suited for the simulation of flows involving complex free-surface deformation. However, the analysis of turbulent modeling for particle-based methods is relatively scarce in the literature. In this work, an analysis of a hybrid RANS-LES turbulence model adapted for the Moving Particle Semi-implicit (MPS) method is performed. In the turbulence model, a zero-equation RANS is applied near the wall boundaries and a standard Smagorinsky LES model is applied elsewhere. Given that the eddy viscosity of the turbulent modeling depends on the distance between the fluid and the nearest wall particle, the calculation of the fluid-wall particle distance may demand a high computational cost due to undefined topology among moving particles. In this way, a method based on the cell-linked list is proposed to improve the nearest wall search for the turbulence model. The implementation is verified through simulation of a lid-driven flow with Reynolds number between 10,000$$ \mathrm{10,000} $$ and 50,000$$ \mathrm{50,000} $$. The result shows that despite the overhead when the turbulence model is adopted, the time needed to reach steady state is shortened so that the overall computational costs are almost the same. In addition, the improvement due to the adoption of turbulence model is more evident for the highest Reynolds numbers. As an application, the flow around a submerged square cylinder near the surface with Reynolds number of 25,000$$ \mathrm{25,000} $$ is simulated. The influences of the cylinder submergence depths on the drag and lift coefficients are investigated for a range of depth-to-length ratios between 0.3$$ 0.3 $$ and 3.0$$ 3.0 $$. When the turbulence model is applied, a smoother convergence tendency is obtained as the resolution increases. Moreover, the flow around the square cylinder is better represented, resulting in more regular vortex shedding. Different flow behaviors were identified around the square cylinder as the submergence depth changes.

We present a numerical framework based on the Cahn-Hilliard-Navier-Stokes (CHNS) model to simulate biphasic flow in confined environments. After deriving the mathematical model, we develop the weak form of the system of PDEs using a pedagogical approach to enable its implementation in FEniCS. The model is validated against experimental data from the literature and subsequently applied to a microfluidic experiment conducted by the authors. All data and code related to this work are available on GitHub.

ABSTRACT

This study presents a numerical framework for modeling two-phase flow in confined environments, focusing on the interplay between capillary and viscous forces. The model integrates the Cahn-Hilliard and Navier-Stokes (CH-NS) equations, utilizing a diffuse-interface approach to capture interfacial dynamics without the limitations of sharp-interface models. Implemented in the finite element platform FEniCS, the framework incorporates Dirichlet boundary conditions to model a fully non-wetting phase. The validation of the proposed model is achieved through two applications: The retraction of an oil droplet from a capillary tube and the drainage of water-wet microfluidic chips. Numerical results align with experimental data, demonstrating the framework's ability to replicate interfacial behaviors, including capillary-driven dynamics and fingering phenomena. This work provides a versatile computational tool for studying immiscible fluid flow, offering potential for advancements in fundamental research on microfluidics, enhanced oil recovery, and remediation of contaminated soil.

Publication date: 15 February 2026

Source: Journal of Computational Physics, Volume 547

Author(s): Gaurav Kumar, Aditya G. Nair

Publication date: 15 February 2026

Source: Journal of Computational Physics, Volume 547

Author(s): Zecheng Zhang, Christian Moya, Lu Lu, Guang Lin, Hayden Schaeffer

Publication date: 15 February 2026

Source: Journal of Computational Physics, Volume 547

Author(s): Arjun Ajay, Jagdeep Singh, Sebastiano Stipa, Pierre Bénard, Joshua Brinkerhoff

Publication date: Available online 15 December 2025

Source: Journal of Computational Physics

Author(s): Qian Wang, Wenshu Zha, Daolun Li, Xiang Li, Luhang Shen, Zhengzheng Shi

Publication date: Available online 13 December 2025

Source: Journal of Computational Physics

Author(s): Anjia Ying, Zhigang Li, Lin Fu

Publication date: Available online 14 December 2025

Source: Journal of Computational Physics

Author(s): Song bai, Michael Liu, Craig schroeder

Publication date: 15 February 2026

Source: Journal of Computational Physics, Volume 547

Author(s): Jiachun Zheng, Yunqing Huang, Nianyu Yi

Publication date: 15 February 2026

Source: Journal of Computational Physics, Volume 547

Author(s): Davide Elia De Falco, Enrico Schiassi, Francesco Calabrò

Publication date: 15 February 2026

Source: Journal of Computational Physics, Volume 547

Author(s): Eviatar Bach, Ricardo Baptista, Edoardo Calvello, Bohan Chen, Andrew Stuart

Publication date: 15 February 2026

Source: Journal of Computational Physics, Volume 547

Author(s): Huangxin Chen, Piaopiao Dong, Dong Wang, Xiao-Ping Wang

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Volume 26, Issue 5, May 2025, Page 174-195
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Volume 26, Issue 5, May 2025, Page 153-173
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Physics of Fluids, Volume 35, Issue 4, April 2023.
This paper proposes a versatile and robust immersed edge-based smoothed finite element method with the mass conservation algorithm (IESFEM/Mass) to solve partitioned fluid–structure interaction (FSI). A gradient smoothing technique was used to solve the system governing equations, which can improve the calculated capability of the linear triangular elements in two phases. Based on the quadratic sharp interface representation of immersed boundary, an extended fictitious domain constructed by a least squares method approximately corrected the residual flux error. The compatibility for boundary conditions on moving interfaces was satisfied, thus eliminating spurious oscillations. The results from all numerical examples were consistent with those from the existing experiments and published numerical solutions. Furthermore, the present divergence-free vector field had a faster-converged rate in the flow velocity, pressure, and FSI force. Even if in distorted meshes, the proposed algorithm maintained a stable accuracy improvement. The aerodynamics of one- and two-winged flapping motions in insect flight has been investigated through the IESFEM/Mass. It can be seen that the wing–wake interaction mechanism is a vital factor affecting the lift. The applicability of the present method in the biological FSI scenario was also well-demonstrated.

Physics of Fluids, Volume 35, Issue 4, April 2023.
We report a pore-scale numerical study of salt finger convection in porous media, with a focus on the influence of the porosity in the non-Darcy regime, which has received little attention in previous research. The numerical model is based on the lattice Boltzmann method with a multiple-relaxation-time scheme and employs an immersed boundary method to describe the fluid–solid interaction. The simulations are conducted in a two-dimensional, horizontally periodic domain with an aspect ratio of 4, and the porosity [math] is varied from 0.7 to 1, while the solute Rayleigh number [math] ranges from [math] to [math]. Our results show that, for all explored [math], solute transport first enhances unexpectedly with decreasing [math] and then decreases when [math] is smaller than a [math]-dependent value. On the other hand, while the flow strength decreases significantly as [math] decreases at low [math], it varies weakly with decreasing [math] at high [math] and even increases counterintuitively for some porosities at moderate [math]. Detailed analysis of the salinity and velocity fields reveals that the fingered structures are blocked by the porous structure and can even be destroyed when their widths are larger than the pore scale, but become more ordered and coherent with the presence of porous media. This combination of opposing effects explains the complex porosity dependencies of solute transport and flow strength. The influence of porous structure arrangement is also examined, with stronger effects observed for smaller [math] and higher [math]. These findings have important implications for passive control of mass/solute transport in engineering applications.

Physics of Fluids, Volume 35, Issue 4, April 2023.
The linear stability of a fully developed liquid–metal magnetohydrodynamic pipe flow subject to a transverse magnetic field is studied numerically. Because of the lack of axial symmetry in the mean velocity profile, we need to perform a BiGlobal stability analysis. For that purpose, we develop a two-dimensional complex eigenvalue solver relying on a Chebyshev–Fourier collocation method in physical space. By performing an extensive parametric study, we show that in contrast to the Hagen–Poiseuille flow known to be linearly stable for all Reynolds numbers, the magnetohydrodynamic pipe flow with transverse magnetic field is unstable to three-dimensional disturbances at sufficiently high values of the Hartmann number and wall conductance ratio. The instability observed in this regime is attributed to the presence of velocity overspeed in the so-called Roberts layers and the corresponding inflection points in the mean velocity profile. The nature and characteristics of the most unstable modes are investigated, and we show that they vary significantly depending on the wall conductance ratio. A major result of this paper is that the global critical Reynolds number for the magnetohydrodynamic pipe flow with transverse magnetic field is Re = 45 230, and it occurs for a perfectly conducting pipe wall and the Hartmann number Ha = 19.7.

Physics of Fluids, Volume 35, Issue 4, April 2023.
In this paper, a model of the development of a quantum turbulence in its initial stage is proposed. The origin of the turbulence in the suggested model is the decay of vortex loops with an internal structure. We consider the initial stage of this process, before an equilibrium state is established. As result of our study, the density matrix of developing turbulent flow is calculated. The quantization scheme of the classical vortex rings system is based on the approach proposed by the author earlier.

Physics of Fluids, Volume 35, Issue 4, April 2023.
A five-stage centrifugal pump is utilized to investigate the interstage flow characteristics of the multistage centrifugal pump as turbine (PAT). The simulation results of performance are verified by comparing with the experimental results. Owing to the distinct structural attributes, significant differences in flow occur between the first stage and the other stages of the multistage PAT. To enhance the understanding of these disparities and explore their repercussions, this study focuses on analyzing the flow within the impellers in the first and second stages by a deterministic analysis. The main conclusions are as follows: The discrepancies in the inflow conditions are the major reason for the dissimilarities in the flow of impellers between stages. The impact loss generated by the misalignment between the positive guide vane outlet angle and the impeller inlet angle leads to flow deviation between impeller passages and affects the internal flow pattern. The unsteadiness under low flow rates is mostly produced by the spatial gradient of the blade-to-blade nonuniformities, which is relevant to the relative position between blades and the positive guide vanes. At high flow rates, especially in the second-stage impeller, the pure unsteady term is the primary cause of flow unsteadiness as a result of the flow separation induced by interactions between the blades and the positive guide vanes. This study can provide some references for the practical operation and performance optimization of the multistage PATs in the future.

Physics of Fluids, Volume 35, Issue 4, April 2023.
Direct simulations of phase-change and phase-ordering phenomena are becoming more common. Recently, qualitative simulations of boiling phenomena have been undertaken by a large number of research groups. One seldom discussed limitation is that large values of gravitational forcing are required to simulate the detachment and rise of bubbles formed at the bottom surface. The forces are typically so large that neglecting the effects of varying pressure in the system becomes questionable. In this paper, we examine the effect of large pressure variations induced by gravity using pseudopotential lattice Boltzmann simulations. These pressure variations lead to height dependent conditions for phase coexistence and nucleation of either gas or liquid domains. Because these effects have not previously been studied in the context of these simulation methods, we focus here on the phase stability in a one-dimensional system, rather than the additional complexity of bubble or droplet dynamics. Even in this simple case, we find that the different forms of gravitational forces employed in the literature lead to qualitatively different phenomena, leading to the conclusion that the effects of gravity induced pressure variations on phase-change phenomena should be very carefully considered when trying to advance boiling and cavitation as well as liquefaction simulations to become quantitative tools.

Physics of Fluids, Volume 35, Issue 4, April 2023.
Capillary desaturation process was investigated as a function of wetting phase rheological signatures during the injection of Newtonian and non-Newtonian fluids. Two sets of two-phase imbibition flow experiments were conducted on a water-wet sandstone core sample using brine and viscoelastic polymer solutions. During the experiments, a high-resolution micro-computed tomography scanner was employed to directly map pore-level fluid occupancies within the pore space. The results of the experiments revealed that at a given capillary number, the viscoelastic polymer was more efficient than the brine in recovering the non-wetting oil phase. At low capillary numbers, this is attributed to the improved accessibility of the viscoelastic polymer solution to the entrance of pore elements, which suppressed snap-off events and allowed more piston-like and cooperative pore-body filling events to contribute to oil displacement. For intermediate capillary numbers, the onset of elastic turbulence caused substantial desaturation, while at high capillary numbers, the superimposed effects of higher viscous and elastic forces further improved the mobilization of the trapped oil ganglia by the viscoelastic polymer. In the waterflood, however, the mobilization of oil globules was the governing recovery mechanism, and the desaturation process commenced only when the capillary number reached a threshold value. These observations were corroborated with the pore-level fluid occupancy maps produced for the brine and viscoelastic polymer solutions during the experiments. Furthermore, at the intermediate and high capillary numbers, the force balance and pore-fluid occupancies suggested different flow regimes for the non-Newtonian viscoelastic polymer. These regions are categorized in this study as elastic-capillary- and viscoelastic-dominated flow regimes, different from viscous-capillary flow conditions that are dominant during the flow of Newtonian fluids. Moreover, we have identified novel previously unreported pore-scale displacement events that take place during the flow of viscoelastic fluids in a natural heterogeneous porous medium. These events, including coalescence, fragmentation, and re-entrapment of oil ganglia, occurred before the threshold of oil mobilization was reached under the elastic-capillary-dominated flow regime. In addition, we present evidence for lubrication effects at the pore level due to the elastic properties of the polymer solution. Furthermore, a comparison of capillary desaturation curves generated for the Newtonian brine and non-Newtonian viscoelastic polymer revealed that the desaturation process was more significant for the viscoelastic polymer than for the brine. Finally, the analysis of trapped oil clusters showed that the ganglion size distribution depends on both the capillary number and the rheological properties of fluids.

Physics of Fluids, Volume 35, Issue 4, April 2023.
The objective of this research paper is to relate the influence of dynamic wetting in a liquid/liquid/solid system to the breakup of emulsion droplets in capillaries. Therefore, modeling and simulation of liquid/liquid flow through a capillary constriction have been performed with varying dynamic contact angles from highly hydrophilic to highly hydrophobic. Advanced advection schemes with geometric interface reconstruction (isoAdvector) are incorporated for high interface advection accuracy. A sharp surface tension force model is used to reduce spurious currents originating from the numerical treatment and geometric reconstruction of the surface curvature at the interface. Stress singularities from the boundary condition at the three-phase contact line are removed by applying a Navier-slip boundary condition. The simulation results illustrate the strong dependency of the wettability and the contact line and interface deformation.

Physics of Fluids, Volume 35, Issue 4, April 2023.
The exact regularized point particle method is used to characterize the turbulence modulation in two-way momentum-coupled direct numerical simulations of a turbulent pipe flow. The turbulence modification is parametrized by the particle Stokes number, the mass loading, and the particle-to-fluid density ratio. The data show that in the wide region of the parameter space addressed in the present paper, the overall friction drag is either increased or unaltered by the particles with respect to the uncoupled case. In the cases where the wall friction is enhanced, the fluid velocity fluctuations show a substantial modification in the viscous sub-layer and in the buffer layer. These effects are associated with a modified turbulent momentum flux toward the wall. The particles suppress the turbulent fluctuations in the buffer region and concurrently provide extra stress in the viscous sub-layer. The sum of the turbulent stress and the extra stress is larger than the Newtonian turbulent stress, thus explaining the drag increase. The non-trivial turbulence/particles interaction turns out in a clear alteration of the near-wall flow structures. The streamwise velocity streaks lose their spatial coherence when two-way coupling effects are predominant. This is associated with a shift of the streamwise vortices toward the center of the pipe and with the concurrent presence of small-scale and relatively more intense vortical structures near the wall.

Physics of Fluids, Volume 35, Issue 4, April 2023.
The wetting of thin films depends critically on the sign of the spreading coefficient [math]. We discuss the cases S < 0, S = 0, and S > 0 for transient models with contact line dissipation and find that the use of a dynamic contact angle solves problems for S > 0 that models might otherwise have. For initial data with a non-zero slope and S > 0, we show that there exists a finite time [math] at which the contact angle of the thin film goes to zero. Then, a molecular precursor emerges from the thin film and moves outward at a constant velocity.

Abstract Graphic Abstract