Eirik Grude Flekkøy

• Reis, Paula Kozlowski Pitombeira; Flekkøy, Eirik Grude; Toussaint, Renaud & Måløy, Knut Jørgen (2026). Linear response theory of front back-contraction during a single Haines jump. Journal of Fluid Mechanics. ISSN 0022-1120. 1041. doi: 10.1017/jfm.2026.11960. Fulltekst i vitenarkiv Vis sammendrag

  We study the linear response of a fluid–fluid interface in a porous medium subjected to a localised, transient perturbation. A single pore is driven out of mechanical equilibrium by a small displacement, initiating a back-contraction of the interface. Assuming negligible total flow, the interface relaxes with a time- and space-dependent profile h(x,t), modelled for a flat geometry. This set-up reflects conditions achievable experimentally using a localised heterogeneity in pore-throat sizes. We determine the evolving interface shape during the relaxation process, together with the associated pressure and velocity fields, using both analytical calculations and pore-network simulations.

• Haghani, Reza; Berg, Carl Fredrik & Flekkøy, Eirik Grude (2026). Droplet shrinkage in phase-field approaches: A comparison of the Allen-Cahn and the Cahn-Hilliard models. Physical Review E (PRE). ISSN 2470-0045. 113(5). doi: 10.1103/y6sf-3lf2. Fulltekst i vitenarkiv
• Xu, Yao; Moura, Marcel; Flekkøy, Eirik Grude & Måløy, Knut Jørgen (2026). A comparison of different image analysis techniques for mapping spatiotemporal pH and carbon dissolution in density-driven convection of CO2 in water. Advances in Water Resources. ISSN 0309-1708. 212. doi: 10.1016/j.advwatres.2026.105296. Fulltekst i vitenarkiv
• Haghani, Reza; Berg, Carl Fredrik & Flekkøy, Eirik Grude (2026). A note on the summation relation in the Cahn-Hilliard equation. AIP Advances. 16(2). doi: 10.1063/5.0316195. Fulltekst i vitenarkiv
• Dodangeh, A.; Toussaint, Renaud; Flekkøy, Eirik Grude & Fahs, M. (2025). Managing seismicity and characterizing reservoirs to enable geothermal energy development while minimizing seismic risk and impacts. doi: 10.3997/2214-4609.202521178. Fulltekst i vitenarkiv
• Flekkøy, Eirik Grude; Hansen, Alex & Eiser, Erika (2025). Heat and superdiffusive melting fronts in unsaturated porous media. Frontiers in Physics. 13. doi: 10.3389/fphy.2025.1610082. Fulltekst i vitenarkiv Vis sammendrag

  When water is present in a medium with pore sizes in a range of approximately 10 nm, the corresponding freezing-point depression will cause long-range broadening of a melting front. Describing the freezing-point depression by the Gibbs–Thomson equation and the pore-size distribution by a power law, we derive a nonlinear diffusion equation for the fraction of melted water. This equation yields superdiffusive spreading of the melting front with a diffusion exponent, which is given by the spatial dimension and the exponent describing the pore size distribution. We derive this solution analytically from energy conservation in the limit where all the energy is consumed by the melting and explore the validity of this approximation numerically. Finally, we explore a geological application of the theory to the case of one-dimensional subsurface melting fronts in granular or soil systems. These fronts, which are produced by heating of the surface, spread at a superdiffusive rate and affect the subsurface to significantly larger depths than a system without the effects of freezing-point depression.

• Flekkøy, Eirik Grude; Hansen, Alex & Eiser, Erika (2025). Heat and super-diffusive melting fronts in unsaturated porous media. http://arxiv.org/abs/cond-mat. doi: https:/arxiv.org/pdf/2508.05451. Fulltekst i vitenarkiv Vis sammendrag

  When water is present in a medium with pore sizes in a range of approximately 10 nm, the corresponding freezing-point depression will cause long-range broadening of a melting front. Describing the freezing-point depression by the Gibbs–Thomson equation and the pore-size distribution by a power law, we derive a nonlinear diffusion equation for the fraction of melted water. This equation yields superdiffusive spreading of the melting front with a diffusion exponent, which is given by the spatial dimension and the exponent describing the pore size distribution. We derive this solution analytically from energy conservation in the limit where all the energy is consumed by the melting and explore the validity of this approximation numerically. Finally, we explore a geological application of the theory to the case of one-dimensional subsurface melting fronts in granular or soil systems. These fronts, which are produced by heating of the surface, spread at a superdiffusive rate and affect the subsurface to significantly larger depths than a system without the effects of freezing-point depression.

• Moura, Marcel; Kern, Vanessa Ruth; Måløy, Knut Jørgen; Carlson, Andreas & Flekkøy, Eirik Grude (2025). Droplet spreading in a wedge: a route to fluid rheology for power-law liquids. Soft Matter. ISSN 1744-683X. 21(36), s. 7014–7020. doi: 10.1039/d5sm00286a. Fulltekst i vitenarkiv Vis sammendrag

  Measuring the rheology of liquids typically requires precise control over shear rates and stresses. Here, we describe an alternative route for predicting the characteristic features of a power-law fluid by simply observing the capillary spreading dynamics of viscous droplets in a wedge-shaped geometry. In this confined setting, capillary and viscous forces interact to produce a spreading dynamics described by anomalous diffusion, a process where the front position grows as a power-law in time with an exponent that differs from the value 1/2 found in classical diffusion. We derive a nonlinear diffusion equation that captures this behavior, and we show that the diffusion exponent is directly related to the rheological exponent of the fluid. We verify this relationship by using both experiments and simulations for different power-law fluids. As the predictions are independent from flow-specific details, this approach provides a robust tool for inferring rheological properties from the spreading dynamics.

• Beechey-Newman, Ilaria; Kizilova, Natalya; Hennig, Andreas Andersen; Flekkøy, Eirik Grude & Eiser, Erika (2025). Confined colloidal droplets dry to form circular mazes. Proceedings of the National Academy of Sciences of the United States of America (PNAS). ISSN 0027-8424. 122(32). doi: 10.1073/pnas.2508363122. Fulltekst i vitenarkiv Vis sammendrag

  During drying, particle-laden sessile droplets will leave so-called coffee-stain rings behind. This phenomenon is well known and well understood (Deegan et al ., Nature 389 , 827–829 (1997). Here, we show that when particle-laden droplets confined in a slit are allowed to evaporate very slowly, they do not deposit coffee rings, but form surprisingly intricate, circular maze-like patterns. We present experiments that illustrate this pattern formation and discuss the factors that determine when such patterns can form. We are not aware of reports of natural examples of the formation of such beautiful patterns under confinement, although it seems likely that they exist.

• Fu, Yuequn & Flekkøy, Eirik Grude (2025). Molecular simulations of cavitation bubble dynamics. Frontiers in Physics. 13. doi: 10.3389/fphy.2025.1614785. Fulltekst i vitenarkiv Vis sammendrag

  We study the cavitation bubble that forms as a nano-scale spherical surface is detached from a flat surface using molecular dynamics (MD) simulations. This investigation maps the onset and early development stages of cavitation at the nanoscale. We study the effects of variable pulling speeds and ambient pressures on the dynamics of the vapor bubble. It was observed that a higher pulling speed increases the cavitation volume but reduces the bubble’s lifetime. On the other hand, ambient pressure variations significantly influence both the maximum volume and the collapse rate of the cavitation. The results are summarized in a phase diagram that displays the effects of these varying pulling speeds and ambient pressures. Significantly, the study corroborates a Family-Vicsek scaling law for the bubble volume evolution.

• Khobaib, Khobaib; Reis, Paula Kozlowski Pitombeira; Moura, Marcel; Toussaint, Renaud; Flekkøy, Eirik Grude & Måløy, Knut Jørgen (2025). Gravity stabilized drainage in porous media with controlled disorder. Physical Review Research (PRResearch). 7(2). doi: 10.1103/PhysRevResearch.7.023040. Fulltekst i vitenarkiv Vis sammendrag

  This work presents an experimental, numerical, and theoretical investigation of slow drainage processes in porous media, focusing on systematic variations in pore-scale disorder. We examine a system comprising a monolayer of cylinders in a quasi-two-dimensional (2D) geometry, where the medium's disorder is controlled via a disorder parameter, 𝜀. By systematically altering 𝜀, we randomly shift the positions of the cylinders and analyze the resulting effects on the gravity stabilized invasion front. Our results show that increasing 𝜀 has a significant impact on the stable width of the invasion front, with this width scaling with the disorder parameter according to an exponent 𝛽=0.57, which closely matches the theoretical value predicted by percolation theory for 2D systems. Additionally, we derive a reciprocal relationship between the dimensionless fluctuation number and the disorder parameter 𝜀. Moreover, we find a correlation between the invasion front width and the size of trapped clusters in the system, and we explore how pore disorder affects the air saturation left behind the invasion front. Both our experimental and numerical findings exhibit exponent values that align with theoretical scaling predictions. This study advances the current understanding of multiphase flows in porous media by specifically addressing the influence of pore-scale disorder on the morphology of invasion fronts.

• Birgisson, Hilmar Yngvi; Xu, Yao; Moura, Marcel; Flekkøy, Eirik Grude & Måløy, Knut Jørgen (2025). Mapping dissolved carbon in space and time: An experimental technique for the measurement of pH and total carbon concentration in density driven convection of CO2 dissolved in water. Advances in Water Resources. ISSN 0309-1708. 198. doi: 10.1016/j.advwatres.2025.104916. Fulltekst i vitenarkiv
• Reis, Paula Kozlowski Pitombeira; Linga, Gaute; Moura, Marcel; Rikvold, Per Arne; Toussaint, Renaud & Flekkøy, Eirik Grude [Vis alle 7 forfattere av denne artikkelen] (2025). Interaction between corner and bulk flows during drainage in granular porous media. Advances in Water Resources. ISSN 0309-1708. 198. doi: 10.1016/j.advwatres.2025.104914. Fulltekst i vitenarkiv
• Kings, Jonathan; Folkow, Lars; Hammer, Øyvind; Kjelstrup, Signe; Mason, Matthew J. & Xiong, Fengzhu [Vis alle 7 forfattere av denne artikkelen] (2025). A model for maxilloturbinate morphogenesis in seals. PLOS ONE. 20(3). doi: 10.1371/journal.pone.0316669. Fulltekst i vitenarkiv
• Combriat, Thomas Michel Daniel; Dysthe, Dag Kristian & Flekkøy, Eirik Grude (2024). Cavitation dynamics in creeping flow. Journal of Fluid Mechanics. ISSN 0022-1120. 999. doi: 10.1017/jfm.2024.937. Fulltekst i vitenarkiv Vis sammendrag

  We investigate the heterogeneous cavitation phenomenon in water when a spherical surface is abruptly separated from a nearby flat substrate, at a distance of approximately 10 nm. By tracking the surface separation using Newton ring positions, and capturing the bubble evolution with a high-speed camera on a microscope, we compare our experimental findings with hydrodynamic predictions at low Reynolds numbers. Upon upward movement of the spherical surface, the resulting bubble develops branched fingers through the Saffman–Taylor instability. Simultaneously, negative liquid pressures in the range ∼ 10 atm are observed. These large tension values occasionally lead to secondary nucleation events. The bubble sizes satisfy a predicted Family–Vicsek scaling law where the bubble area is proportional to the inverse bubble lifetime. The fact that creeping flow cavitation bubbles are more short-lived the larger they are separates them from bubbles that are governed by inertial dynamics.

• Cheon, Hyejeong; Kizilova, Nataliya; Flekkøy, Eirik Grude; Mason, Matthew J.; Folkow, Lars & Kjelstrup, Signe (2024). The nasal cavity of the bearded seal: An effective and robust organ for retaining body heat and water. Journal of Theoretical Biology. ISSN 0022-5193. 595, s. 1–12. doi: 10.1016/j.jtbi.2024.111933. Fulltekst i vitenarkiv Vis sammendrag

  We report the effects of varying physiological and other properties on the heat and water exchange in the maxilloturbinate structure (MT) of the bearded seal (Erignathus barbatus or Eb) in realistic environments, using a computational fluid dynamics (CFD) model. We find that the water retention in percent is very high (about 90 %) and relatively unaffected by either cold (−30 °C) or warm (10 °C) conditions. The retention of heat is also high, around 80 % . Based on a consideration of entropy production by the maxilloturbinate system, we show that anatomical and physiological properties of the seal provide good conditions for heat and water exchange at the mucus lining in the seal’s nasal cavity. At normal values of tidal volume and maxilloturbinate (MT) length, the air temperature in the MT reaches the body temperature before the air has left the MT channels. This confers a safety factor which is expected to be helpful in exercise, when ventilation increases.

• Haghanihasanabadi, Reza; Gahrooei, Hamidreza Erfani; McClure, James E.; Flekkøy, Eirik Grude & Berg, Carl Fredrik (2024). Color-gradient-based phase-field equation for multiphase flow. Physical Review E (PRE). ISSN 2470-0045. 109(3). doi: 10.1103/PhysRevE.109.035301. Fulltekst i vitenarkiv Vis sammendrag

  In this paper, the underlying problem with the color-gradient (CG) method in handling density-contrast fluids is explored. It is shown that the CG method is not fluid invariant. Based on nondimensionalizing the CG method, a phase-field interface-capturing model is proposed which tackles the difficulty of handling density-contrast fluids. The proposed formulation is developed for incompressible, immiscible two-fluid flows without phase-change phenomena, and a solver based on the lattice Boltzmann method is proposed. Coupled with an available robust hydrodynamic solver, a binary fluid flow package that handles fluid flows with high density and viscosity contrasts is presented. The macroscopic and lattice Boltzmann equivalents of the formulation, which make the physical interpretation of it easier, are presented. In contrast to existing color-gradient models where the interface-capturing equations are coupled with the hydrodynamic ones and include the surface tension forces, the proposed formulation is in the same spirit as the other phase-field models such as the Cahn-Hilliard and the Allen-Cahn equations and is solely employed to capture the interface advected due to a flow velocity. As such, similarly to other phase-field models, a so-called mobility parameter comes into play. In contrast, the mobility is not related to the density field but a constant coefficient. This leads to a formulation that avoids individual speed of sound for the different fluids. On the lattice Boltzmann solver side, two separate distribution functions are adopted to solve the formulation, and another one is employed to solve the Navier-Stokes equations, yielding a total of three equations. Two series of numerical tests are conducted to validate the accuracy and stability of the model, where we compare simulated results with available analytical and numerical solutions, and good agreement is observed. In the first set the interfacial evolution equations are assessed, while in the second set the hydrodynamic effects are taken into account.

• Reis, Paula Kozlowski Pitombeira; Linga, Gaute; Moura, Marcel; Rikvold, Per Arne; Toussaint, Renaud & Flekkøy, Eirik Grude [Vis alle 7 forfattere av denne artikkelen] (2024). Interaction between corner and bulk flows during drainage in granular porous media. arXiv.org. ISSN 2331-8422. doi: 10.48550/arXiv.2409.05574. Fulltekst i vitenarkiv
• Olsen, Kristian Stølevik; Hansen, Alex & Flekkøy, Eirik Grude (2024). Hyper-Ballistic Superdiffusion of Competing Microswimmers. Entropy. 26(3), s. 1–8. doi: 10.3390/e26030274. Fulltekst i vitenarkiv Vis sammendrag

  Hyper-ballistic diffusion is shown to arise from a simple model of microswimmers moving through a porous media while competing for resources. By using a mean-field model where swimmers interact through the local concentration, we show that a non-linear Fokker–Planck equation arises. The solution exhibits hyper-ballistic superdiffusive motion, with a diffusion exponent of four. A microscopic simulation strategy is proposed, which shows excellent agreement with theoretical analysis.

• Cheon, Hyejeong; Kjelstrup, Signe; Kizilova, Nataliya; Flekkøy, Eirik Grude; Mason, Matthew J. & Folkow, Lars (2023). Structure-function relationships in the nasal cavity of Arctic and subtropical seals. Biophysical Journal. ISSN 0006-3495. 122(24), s. 4686–4698. doi: 10.1016/j.bpj.2023.11.012. Fulltekst i vitenarkiv Vis sammendrag

  The heating and moistening of inhaled air, and the cooling and moisture removal from exhaled air, are crucial for the survival of animals under severe environmental conditions. Arctic mammals have evolved specific adaptive mechanisms to retain warmth and water and restrict heat loss during breathing. Here, the role of the porous turbinates of the nasal cavities of Arctic and subtropical seals is studied with this in mind. Mass and energy balance equations are used to compute the time-dependent temperature and water vapor profiles along the nasal passage. A quasi-1D model based on computed tomography images of seal nasal cavities is used in numerical simulations. Measured cross-sectional areas of the air channel and the perimeters of the computed tomography slices along the nasal cavities of the two seal species are used. The model includes coupled heat and vapor transfer at the air-mucus interface and heat transfer at the interfaces between the tissues and blood vessels. The model, which assumes constant blood flow to the nose, can be used to predict the temperature of the exhaled air as a function of ambient temperature. The energy dissipation (entropy production) in the nasal passages was used to measure the relative importance of structural parameters for heat and water recovery. We found that an increase in perimeter led to significant decreases in the total energy dissipation. This is explained by improved conditions for heat and water transfer with a larger complexity of turbinates. Owing to differences in their nasal cavity morphology, the Arctic seal is expected to be advantaged in these respects relative to the subtropical seal.

• Flekkøy, Eirik Grude & Toussaint, Renaud (2023). Statistical implications of the n = 1 observation of 1I/'Oumuamua. Monthly Notices of the Royal Astronomical Society: Letters (MNRAS Letters). ISSN 1745-3925. 523(1), s. L9–L14. doi: 10.1093/mnrasl/slad049. Fulltekst i vitenarkiv Vis sammendrag

  ABSTRACT We obtain the exact statistical distribution of expected detection rates that may be obtained from the detection of ‘Oumuamua, which currently belongs to a class of objects that is only observed once in our Solar system. The derivation of the distribution of future detection rates starts from the assumption that the detection is a result of a Poisson process, and uses Bayes theorem along with information theory to get the result. We derive the probability for the next such observation along with the confidence limits of this prediction assuming that observations are done with the forthcoming Vera C. Rubin Observatory. This probability depends on the estimates of detection rates that existed prior to the ‘Oumuamua observation. However, unless the constraints given by these model-based estimates are within an order of magnitude of the actual detection rate, they have a negligible effect on the probability of making a second observation. The results are generalized to the expected future case where more than one observation exists.

• Hansen, Alex; Flekkøy, Eirik Grude; Sinha, Santanu & Slotte, Per Arne (2023). A statistical mechanics for immiscible and incompressible to-phase flow in porous media. Advances in Water Resources. ISSN 0309-1708. 171. doi: 10.1016/j.advwatres.2022.104336. Fulltekst i vitenarkiv
• Thorens, Louison; Måløy, Knut Jørgen; Flekkøy, Eirik Grude; Sandnes, Bjørnar; Bourgoin, Mickaël & Santucci, Stephane F A (2023). Capillary washboarding during slow drainage of a frictional fluid. Soft Matter. ISSN 1744-683X. doi: 10.1039/d3sm00717k. Fulltekst i vitenarkiv Vis sammendrag

  Numerous natural and industrial processes involve the mixed displacement of liquids, gases and granular materials through confining structures. However, understanding such three-phase flows remains a formidable challenge, despite their tremendous economic and environmental impact. To unveil the complex interplay of capillary and granular stresses in such flows, we consider here a model configuration where a frictional fluid (an immersed sedimented granular layer) is slowly drained out of a horizontal capillary. Analyzing how liquid/air menisci displace particles from such granular beds, we reveal various drainage patterns, notably the periodic formation of dunes, analogous to road washboard instability. Considering the competitive role of friction and capillarity, a 2D theoretical approach supported by numerical simulations of a meniscus bulldozing a front of particles provides quantitative criteria for the emergence of those dunes. A key element is the strong increase of the frictional forces, as the bulldozed particles accumulate and bend the meniscus horizontally. Interestingly, this frictional enhancement with the attack angle is also crucial in small-legged animals' locomotion over granular media.

• Zhang, Dawang; Campbell, James; Eriksen, Jon Alm; Flekkøy, Eirik Grude; Måløy, Knut Jørgen & MacMinn, Christopher W. [Vis alle 7 forfattere av denne artikkelen] (2023). Frictional fluid instabilities shaped by viscous forces. Nature Communications. 14(1). doi: 10.1038/s41467-023-38648-6. Fulltekst i vitenarkiv Vis sammendrag

  Multiphase flows involving granular materials are complex and prone to pattern formation caused by competing mechanical and hydrodynamic interactions. Here we study the interplay between granular bulldozing and the stabilising effect of viscous pressure gradients in the invading fluid. Injection of aqueous solutions into layers of dry, hydrophobic grains represent a viscously stable scenario where we observe a transition from growth of a single frictional finger to simultaneous growth of multiple fingers as viscous forces are increased. The pattern is made more compact by the internal viscous pressure gradient, ultimately resulting in a fully stabilised front of frictional fingers advancing as a radial spoke pattern.

• Reis, Paula Kozlowski Pitombeira; Moura, Marcel; Linga, Gaute; Rikvold, Per Arne; Toussaint, Renaud & Flekkøy, Eirik Grude [Vis alle 7 forfattere av denne artikkelen] (2023). A simplified pore-scale model for slow drainage including film-flow effects. Advances in Water Resources. ISSN 0309-1708. 182. doi: 10.1016/j.advwatres.2023.104580. Fulltekst i vitenarkiv Vis sammendrag

  Liquid-filled corners and capillary bridges can establish networks connecting seemingly isolated clusters during drainage in porous media. Coupled with drainage through the bulk of pores and throats, the flow through these networks constitutes a secondary drainage mechanism that can significantly affect fluid configurations and residual saturations. In order to investigate the prevalence of this drainage mechanism, we propose a quasi-static pore-network model based on modifying the trapped-cluster-identification algorithm in an invasion-percolation model. With the modification, wetting-phase connectivity is provided by direct successions of pores and throats, represented by sites and bonds, as well as by chains of interconnected capillary bridges. The advancement of the fluid interface in the porous matrix is determined by the bonds’ invasion thresholds and local capillary pressure values, calculated taking into consideration gravitational effects. With the proposed model, experimentally verified phenomena related to slow drainage in granular porous media are reproduced, showing good qualitative agreement.

• Flekkøy, Eirik Grude; Folkow, Lars; Kjelstrup, Signe; Mason, Matthew J. & Wilhelmsen, Øivind (2023). Thermal modeling of the respiratory turbinates in arctic and subtropical seals. Journal of Thermal Biology. ISSN 0306-4565. 112. doi: 10.1016/j.jtherbio.2022.103402. Fulltekst i vitenarkiv Vis sammendrag

  Mammals possess complex structures in their nasal cavities known as respiratory turbinate bones, which help the animal to conserve body heat and water during respiratory gas exchange. We considered the function of the maxilloturbinates of two species of seals, one arctic (Erignathus barbatus), one subtropical (Monachus monachus). By means of a thermo-hydrodynamic model that describes the heat and water exchange in the turbinate region we are able to reproduce the measured values of expired air temperatures in grey seals (Halichoerus grypus), a species for which experimental data are available. At the lowest environmental temperatures, however, this is only possible in the arctic seal, and only if we allow for the possibility of ice forming on the outermost turbinate region. At the same time the model predicts that for the arctic seals, the inhaled air is brought to deep body temperature and humidity conditions in passing the maxilloturbinates. The modeling shows that heat and water conservation go together in the sense that one effect implies the other, and that the conservation is most efficient and most flexible in the typical environment of both species. By controlling the blood flow through the turbinates the arctic seal is able to vary the heat and water conservation substantially at its average habitat temperatures, but not at temperatures around −40 °C. The subtropical species has simpler maxilloturbinates, and our model predicts that it is unable to bring inhaled air to deep body conditions, even in its natural environment, without some congestion of the vascular mucosa covering the maxilloturbinates. Physiological control of both blood flow rate and mucosal congestion is expected to have profound effects on the heat exchange function of the maxilloturbinates in seals.

• Flekkøy, Eirik Grude; Sandnes, Bjørnar & Måløy, Knut Jørgen (2023). Shape of a frictional fluid finger. Physical Review Fluids. 8(11). doi: 10.1103/PhysRevFluids.8.114302. Fulltekst i vitenarkiv Vis sammendrag

  Frictional fluid dynamics describes the displacement patterns that arise when a confined mixture of liquid and grains are displaced by an immiscible fluid under pressures that are too small to cause drainage into single pores. The flow, which is governed by solid friction and capillary forces, thus bulldozes the grains into compaction fronts which give rise to propagating fingers that eventually interact to create a range of patterns, including labyrinthine ones. We derive an analytic description that successfully reproduces the experimental results for the shape of a single finger as well as the compaction front profile. The theory thus depends on only one fitting parameter.

• Baldelli, Beatrice; Linga, Gaute & Flekkøy, Eirik Grude (2022). Thermal conduction through a cool well. Physical Review Fluids. 7(10). doi: 10.1103/PhysRevFluids.7.103503. Fulltekst i vitenarkiv Vis sammendrag

  We study a differentially heated square cavity with inlet and outlet ports at the top of the side walls, quantifying how the effective thermal conductivity changes with the temperature difference across the system. The side walls are insulating, the top surface is kept at a fixed high temperature, and the bottom surface at a fixed low temperature, leading to buoyancy-stabilized flow. We visualize the flow pattern for Reynolds number, Re=1, and Prandtl number, Pr=50, and characterize the heat transfer at the bottom surface using the Nusselt number, Nu, for Re=0.1,1,10 and Pr=1,50. As the Richardson number, Ri, is increased, we observe the formation of a series of system-spanning vortices through the merging of Moffatt eddies growing from the bottom corners of the cavity. We find that the convection, which enhances the transport of heat, is strongly suppressed by increasing the temperature drop. As a result Nu drops by a factor 1–3 depending on the Reynolds number.

• Haugerud, Ivar Svalheim; Linga, Gaute & Flekkøy, Eirik Grude (2022). Solute dispersion in channels with periodic square boundary roughness. Journal of Fluid Mechanics. ISSN 0022-1120. 944. doi: 10.1017/jfm.2022.522. Fulltekst i vitenarkiv Vis sammendrag

  Transport of solutes through channels with rough boundaries is abundant in natural and engineered settings. However, it is not known currently what the consequences of an abruptly alternating boundary are for the solute dispersion, in particular when advected by inertial fluid flow. To investigate this, we compute numerically the time-asymptotic longitudinal dispersion coefficient of a passive solute advected by fluid flow through a two-dimensional channel with square boundary roughness. We determine how the effective diffusion coefficient depends on the boundary amplitude, Péclet number and Reynolds number. For creeping flow, the effective diffusion coefficient is found to be enhanced significantly through the recirculation zones. Increasing fluid inertia reduces the effective diffusion coefficient by up to a factor of two for high Péclet numbers. We interpret this behaviour by analysing residence times computed from Lagrangian particle simulations.

• Flekkøy, Eirik Grude & Brodin, Joachim Falck (2022). Discerning between Different 'Oumuamua Models by Optical and Infrared Observations. Astrophysical Journal Letters. ISSN 2041-8205. 925(2). doi: 10.3847/2041-8213/ac4b62. Fulltekst i vitenarkiv Vis sammendrag

  Abstract The first interstellar object to be observed in our solar system, 1I/2017 U1 ’Oumuamua, combines the lack of observable cometary activity with an extra-gravitational acceleration. This has given rise to several mutually exclusive explanations based on different assumptions in the material composition of ’Oumuamua. We show how a combination of observations in the infrared and optical spectra may serve to distinguish between these explanations once another object with ’Omuamua-like properties comes close enough to Earth. This possibility is linked to the widely different thermal properties of the different material models that have been proposed. Developing a model for the thermal conduction and infrared signal from a fractal model, we compare predictions of the infrared signal with that from standard thermal models that assume ’Oumuamua to be either a solid piece of rock/ice or a thin sheet.

• Campbell, James; Sandnes, Bjørnar; Flekkøy, Eirik Grude & Måløy, Knut Jørgen (2022). Dynamics of Dendritic Ice Freezing in Confinement. Crystal Growth & Design. ISSN 1528-7483. 22(4), s. 2433–2440. doi: 10.1021/acs.cgd.1c01488. Fulltekst i vitenarkiv Vis sammendrag

  We use high-speed photography to observe the dendritic freezing of ice between two closely spaced parallel plates. Measuring the propagation speeds of dendrites, we investigate whether there is a confinement-induced thermal influence upon the speed beyond that provided by a single surface. Plates of thermally insulating plastic and moderately thermally conductive glass are used alone and in combination, at temperatures between −10.6 and −4.8 °C, with separations between 17 and 135 μm wide. No effect of confinement was detected for propagation on glass surfaces, but a possible slowing of propagation speed was seen between insulating plates. The pattern of dendritic growth was also studied, with a change from curving to straight dendrites being strongly associated with a switch from a glass to a plastic substrate.

• Olsen, Kristian Stølevik; Angheluta, Luiza & Flekkøy, Eirik Grude (2022). Collective states of active matter with stochastic reversals: Emergent chiral states and spontaneous current switching. Physical Review Research (PRResearch). 4(4). doi: 10.1103/PhysRevResearch.4.043017. Fulltekst i vitenarkiv
• Hansen, Alex; Flekkøy, Eirik Grude; Sinha, Santanu & Slotte, Per Arne (2022). A statistical mechanics framework for immiscible and incompressible two-phase flow in porous media. Advances in Water Resources. ISSN 0309-1708. 171. doi: 10.1016/j.advwatres.2022.104336. Fulltekst i vitenarkiv Vis sammendrag

  We construct a statistical mechanics for immiscible and incompressible two-phase flow in porous media under local steady-state conditions based on the Jaynes maximum entropy principle. A cluster entropy is assigned to our lack of knowledge of, and control over, the fluid and flow configurations in the pore space. As a consequence, two new variables describing the flow emerge: The agiture, which describes the level of agitation of the two fluids, and the flow derivative, which is conjugate to the saturation. Agiture and flow derivative are the analogs of temperature and chemical potential in standard (thermal) statistical mechanics. The associated thermodynamics-like formalism reveals a number of hitherto unknown relations between the variables that describe the flow, including fluctuations. The formalism opens for new approaches to characterize porous media with respect to multi-phase flow for practical applications, replacing the simplistic relative permeability theory while still keeping the number of variables tractable.

• Olsen, Kristian Stølevik; Angheluta, Luiza & Flekkøy, Eirik Grude (2021). Active Brownian particles moving through disordered landscapes. Soft Matter. ISSN 1744-683X. doi: 10.1039/d0sm01942a. Fulltekst i vitenarkiv
• Vincent-Dospital, Tom; Toussaint, Renaud; Cochard, Alain; Flekkøy, Eirik Grude & Måløy, Knut Jørgen (2021). Thermal dissipation as both the strength and weakness of matter. A material failure prediction by monitoring creep. Soft Matter. ISSN 1744-683X. 17(15), s. 4143–4150. doi: 10.1039/d0sm02089c. Fulltekst i vitenarkiv Vis sammendrag

  In any domain involving some stressed solids, that is, from seismology to general engineering, the strength of matter is a paramount feature to understand. We here discuss the ability of a simple thermally activated sub-critical model, which includes the auto-induced thermal evolution of cracks tips, to predict the catastrophic failure of a vast range of materials. It is in particular shown that the intrinsic surface energy barrier, for breaking the atomic bonds of many solids, can be easily deduced from the slow creeping dynamics of a crack. This intrinsic barrier is however higher than the macroscopic load threshold at which brittle matter brutally fails, possibly as a result of thermal activation and of a thermal weakening mechanism. We propose a novel method to compute this macroscopic energy release rate of rupture, Ga, solely from monitoring slow creep, and we show that this reproduces the experimental values within 50% accuracy over twenty different materials, and over more than four decades of fracture energy.

• Måløy, Knut Jørgen; Moura, Marcel; Hansen, Alex; Flekkøy, Eirik Grude & Toussaint, Renaud (2021). Burst Dynamics, Upscaling and Dissipation of Slow Drainage in Porous Media. Frontiers in Physics. 9. doi: 10.3389/fphy.2021.796019. Fulltekst i vitenarkiv Vis sammendrag

  We present a theoretical and experimental investigation of drainage in porous media. The study is limited to stabilized fluid fronts at moderate injection rates, but it takes into account capillary, viscous, and gravitational forces. In the theoretical framework presented, the work applied on the system, the energy dissipation, the final saturation and the width of the stabilized fluid front can all be calculated if we know the dimensionless fluctuation number, the wetting properties, the surface tension between the fluids, the fractal dimensions of the invading structure and its boundary, and the exponent describing the divergence of the correlation length in percolation. Furthermore, our theoretical description explains how the Haines jumps’ local activity and dissipation relate to dissipation on larger scales.

• Flekkøy, Eirik Grude; Hansen, Alex & Baldelli, Beatrice (2021). Hyperballistic Superdiffusion and Explosive Solutions to the Non-Linear Diffusion Equation. Frontiers in Physics. 9. doi: 10.3389/fphy.2021.640560. Fulltekst i vitenarkiv Vis sammendrag

  By means of a particle model that includes interactions only via the local particle concentration, we show that hyperballistic diffusion may result. This is done by finding the exact solution of the corresponding non-linear diffusion equation, as well as by particle simulations. The connection between these levels of description is provided by the Fokker-Planck equation describing the particle dynamics.

• Luu, Jane; Flekkøy, Eirik Grude & Toussaint, Renaud (2020). 'Oumuamua as a Cometary Fractal Aggregate: The Dust Bunny Model. Astrophysical Journal Letters. ISSN 2041-8205. 900(2). doi: 10.3847/2041-8213/abafa7. Fulltekst i vitenarkiv
• Xu, Le; Szymczak, Piotr; Toussaint, Renaud; Flekkøy, Eirik Grude & Måløy, Knut Jørgen (2020). Dissolution phase diagram in radial geometry. Frontiers in Physics. 8. doi: 10.3389/fphy.2020.00369. Fulltekst i vitenarkiv Vis sammendrag

  Fractures play an important role as flow paths in porous media. When an undersaturated reactive fluid is flowing in a fracture, the dissolution process will alter the flow paths locally. Dissolution patterns grow slowly, but they may lead to a dramatic reorganization of the flow. Here, we study dissolution in a radial geometry, which is relevant for a number of practical applications, e.g., the acidization of oil reservoirs. Different dissolution patterns are presented in a phase diagram with the Péclet and Damköhler numbers as parameters. We also analyze quantitatively the density of wormholes and the relation between the aperture roughness and the ramified patterns.

• Moura, Marcel; Måløy, Knut Jørgen; Flekkøy, Eirik Grude & Toussaint, Renaud (2020). Intermittent Dynamics of Slow Drainage Experiments in Porous Media: Characterization Under Different Boundary Conditions. Frontiers in Physics. 7. doi: 10.3389/fphy.2019.00217. Fulltekst i vitenarkiv Vis sammendrag

  The intermittent dynamics of slow drainage flows in a porous medium is studied experimentally. This kind of two-phase flow is characterized by a rich burst activity and our setup allows us to characterize those bursts directly via images of the flow and pressure measurements. Two different boundary conditions were analyzed: controlled withdrawal rate (CWR) and controlled imposed pressure (CIP). We have characterized geometrical and statistical properties of the bursts from images and pressure measurements. We have shown that in spite of leading to similar final invasion patterns, some dynamical features of the invasion differ considerably between the CWR and CIP boundary conditions. In particular, their pressure signatures are very distinct, which then translates into very distinct features on the power spectrum density of the pressure signals. A fully integrable analytical framework is presented which successfully describes the scaling features of the power spectrum for the CIP case.

• Vincent-Dospital, Tom; Toussaint, Renaud; Santucci, Stephane; Vanel, Loïc; Bonamy, Daniel & Hattali, Lamine [Vis alle 9 forfattere av denne artikkelen] (2020). How heat controls fracture: the thermodynamics of creeping and avalanching cracks. Soft Matter. ISSN 1744-683X. 16(41), s. 9590–9602. doi: 10.1039/D0SM01062F. Fulltekst i vitenarkiv Vis sammendrag

  While of paramount importance in material science, the dynamics of cracks still lacks a complete physical explanation. The transition from their slow creep behavior to a fast propagation regime is a notable key, as it leads to full material failure if the size of a fast avalanche reaches that of the system. We here show that a simple thermodynamics approach can actually account for such complex crack dynamics, and in particular for the non-monotonic force-velocity curves commonly observed in mechanical tests on various materials. We consider a thermally activated failure process that is coupled with the production and the diffusion of heat at the fracture tip. In this framework, the rise in temperature only affects the sub-critical crack dynamics and not the mechanical properties of the material. We show that this description can quantitatively reproduce the rupture of two different polymeric materials (namely, the mode I opening of polymethylmethacrylate (PMMA) plates, and the peeling of pressure sensitive adhesive (PSA) tapes), from the very slow to the very fast fracturing regimes, over seven to nine decades of crack propagation velocities. In particular, the fastest regime is obtained with an increase of temperature of thousands of kelvins, on the molecular scale around the crack tip. Although surprising, such an extreme temperature is actually consistent with different experimental observations that accompany the fast propagation of cracks, namely, fractoluminescence (i.e., the emission of visible light during rupture) and a complex morphology of post-mortem fracture surfaces, which could be due to the sublimation of bubbles.

• Vincent-Dospital, Tom; Toussaint, Renaud; Cochard, Alain; Måløy, Knut Jørgen & Flekkøy, Eirik Grude (2020). Thermal weakening of cracks and brittle-ductile transition of matter: A phase model. PHYSICAL REVIEW MATERIALS. 4(2). doi: 10.1103/PhysRevMaterials.4.023604. Fulltekst i vitenarkiv Vis sammendrag

  We present a model for the thermally activated propagation of cracks in elastic matrices. The propagation is considered as a subcritical phenomenon, the kinetics of which is described by an Arrhenius law. In this law, we take the thermal evolution of the crack front into account, assuming that a portion of the released mechanical energy is transformed into heat in a zone surrounding the tip. We show that such a model leads to a two-phase crack propagation: the first phase at low velocity in which the temperature elevation is of little effect and the propagation is mainly governed by the mechanical load and by the toughness of the medium, and the second phase in which the crack is thermally weakened and propagates at greater velocity. We illustrate, with numerical simulations of mode I cracks propagating in thin disordered media, how such a dual behavior can explain the usual stick-slip in brittle fracturing. In addition, we predict the existence of a limiting ambient temperature above which the weakened phase ceases to exist and we propose this critical phenomenon as a novel explanation for the brittle-ductile transition of solids.

• Sauermoser, Marco; Kjelstrup, Signe; Kizilova, Nataliya; Pollet, Bruno & Flekkøy, Eirik Grude (2020). Seeking minimum entropy production for a tree-like flow-field in a fuel cell. Physical Chemistry, Chemical Physics - PCCP. ISSN 1463-9076. 22(13), s. 6993–7003. doi: 10.1039/C9CP05394H. Fulltekst i vitenarkiv Vis sammendrag

  Common for tree-shaped, space-filling flow-field plates in polymer electrolyte fuel cells is their ability to distribute reactants uniformly across the membrane area, thereby avoiding excess concentration polarization or entropy production at the electrodes. Such a flow field, as predicted by Murray's law for circular tubes, was recently shown experimentally to give a better polarization curve than serpentine or parallel flow fields. In this theoretical work, we document that a tree-shaped flow-field, composed of rectangular channels with T-shaped junctions, has a smaller entropy production than the one based on Murray's law. The width w0 of the inlet channel and the width scaling parameter, a, of the tree-shaped flow-field channels were varied, and the resulting Peclet number at the channel outlets was computed. We show, using 3D hydrodynamic calculations as a reference, that pressure drops and channel flows can be accounted for within a few percents by a quasi-1D model, for most of the investigated geometries. Overall, the model gives lower energy dissipation than Murray's law. The results provide new tools and open up new possibilities for flow-field designs characterized by uniform fuel delivery in fuel cells and other catalytic systems.

• Olsen, Kristian Stølevik; Angheluta, Luiza & Flekkøy, Eirik Grude (2020). Escape problem for active particles confined to a disk. Physical Review Research (PRResearch). 2(4). doi: 10.1103/PhysRevResearch.2.043314. Fulltekst i vitenarkiv Vis sammendrag

  We study the escape problem for interacting, self-propelled particles confined to a disk, where particles can exit through one open slot on the circumference. Within a minimal two-dimensional Vicsek model, we numerically study the statistics of escape events when the self-propelled particles can be in a flocking state. We show that while an exponential survival probability is characteristic for noninteracting self-propelled particles at all times, the interacting particles have an initial exponential phase crossing over to a subexponential late-time behavior. We use a phenomenological model based on nonstationary Poisson processes which includes the Allee effect to explain this subexponential trend and perform numerical simulations for various noise intensities.

Se alle arbeider i NVA

• Feder, Jens; Flekkøy, Eirik Grude & Hansen, Alex (2022). Physics of Flow in Porous Media. Cambridge University Press. ISBN 9781108989114. 348 s. Fulltekst i vitenarkiv
• Angell, Carl; Flekkøy, Eirik Grude & Kristiansen, Jostein Riiser (2021). Fysikk for lærere. Gyldendal Akademisk. ISBN 9788205533158. 282 s. Fulltekst i vitenarkiv
• Bedeaux, Dick; Flekkøy, Eirik Grude; Hansen, Alex; Kjelstrup, Signe; Måløy, Knut Jørgen & Torsæter, Ole (2020). Physics of Porous Media. Frontiers Media S.A.. ISBN 9782889635351. 173 s. Fulltekst i vitenarkiv

Se alle arbeider i NVA

• Reis, Paula Kozlowski Pitombeira; Flekkøy, Eirik Grude; Toussaint, Renaud & Måløy, Knut Jørgen (2026). Linear Response Theory of Front-Back Contraction During a Single Haines Jump. Fulltekst i vitenarkiv
• Moura, Marcel; Brodin, Joachim Falck; Reis, Paula Kozlowski Pitombeira; Pierce, Kevin; Jankov, Mihailo & Rikvold, Per Arne [Vis alle 11 forfattere av denne artikkelen] (2026). From Thin Films to Stable Fronts: Tabletop Experimental Approaches to 2D and 3D Porous Media Flows. doi: https:/www.youtube.com/live/bSQ-sHK6FTU?si=W9_rbJ5BkyRPHP0m. Fulltekst i vitenarkiv
• Moura, Marcel; Hansen, Alex; Flekkøy, Eirik Grude & Måløy, Knut Jørgen (2026). POROUS MATTER: PoreLab's sci-art adventures in Romania. Fulltekst i vitenarkiv
• Moura, Marcel; Reis, Paula Kozlowski Pitombeira; Rikvold, Per Arne; Linga, Gaute; Flekkøy, Eirik Grude & Schäfer, Gerhard [Vis alle 8 forfattere av denne artikkelen] (2026). Thin Film Flow: Fluid Transport via Thin Liquid Films in Slow Porous Media Flows. Fulltekst i vitenarkiv
• Moura, Marcel; Lanza, Federico; Kern, Vanessa Ruth; Olsen, Pål Eivind; Carlson, Andreas & Måløy, Knut Jørgen [Vis alle 7 forfattere av denne artikkelen] (2026). Instabilities in textured lifted Hele-Shaw cells and bubbly flows in a pipe. Fulltekst i vitenarkiv
• Xu, Yao; Moura, Marcel; Flekkøy, Eirik Grude & Måløy, Knut Jørgen (2025). Quantification for density-driven convection of CO2 in water. Fulltekst i vitenarkiv
• Lanza, Federico; Linga, Gaute; Barras, Fabian; Khobaib, Khobaib; Flekkøy, Eirik Grude & Måløy, Knut Jørgen (2025). From Carbopol to magma: challenges in complex flows through porous and confined media. Fulltekst i vitenarkiv
• Flekkøy, Eirik Grude; Eiser, Erika & Hansen, Alex (2025). Freezing, melting and metastable states in porous media. Fulltekst i vitenarkiv
• Moura, Marcel; Reis, Paula Kozlowski Pitombeira; Rikvold, Per Arne; Linga, Gaute; Flekkøy, Eirik Grude & Schäfer, Gerhard [Vis alle 8 forfattere av denne artikkelen] (2025). Thin Film Flow: Fluid Transport via Thin Liquid Films in Slow Porous Media Flows. Fulltekst i vitenarkiv
• Moura, Marcel; Kern, Vanessa Ruth; Olsen, Pål Eivind; Carlson, Andreas; Måløy, Knut Jørgen & Flekkøy, Eirik Grude (2025). Complex fluids in confinement: spreading in a wedge and instabilities in textured lifted Hele-Shaw cells. Fulltekst i vitenarkiv
• Eiser, Erika; Beechey-Newman, Ilaria; Hennig, Andreas Andersen; Flekkøy, Eirik Grude & Kizilova, Natalya (2025). Pattern Formation in Confined Coffee-Rings. doi: https:/www.flipsnack.com/E677D85569B/understanding-surfaces-and-interfaces/full-view.html. Fulltekst i vitenarkiv Vis sammendrag

  Deegan and coworkers showed, that a simple coffee-drop on a flat surface can produce a dark rim of solid particles (1). Since then many research groups have studied the drying patterns produced by sessile drops of colloidal suspensions, ranging from droplets of blood to technological applications like ink-jet printing (2). Here, I present experiments on the drying of dilute colloidal suspensions in a confined, cylindrical droplet, which can only evaporate radially (3). In such confined systems, circular “coffee-stain” rings may be replaced by a hierarchical drying pattern that results in a connected “labyrinth” of colloid-rich fingers. The characteristic length-scale of this pattern gets abruptly smaller as the droplet shrinks.

• Beechey-Newman, Ilaria; Eiser, Erika; Kizilova, Natalya; Hennig, Andreas Andersen & Flekkøy, Eirik Grude (2025). Confined Colloidal Droplets Dry to Form Circular Mazes. Fulltekst i vitenarkiv
• Beechey-Newman, Ilaria; Eiser, Erika; Hennig, Andreas Andersen; Kizilova, Natalya & Flekkøy, Eirik Grude (2025). Confined Colloidal Droplets Dry to Form Circular Mazes. Fulltekst i vitenarkiv Vis sammendrag

  Drying drops of colloidal suspensions are hugely relevant in microfluidic and printing applications, as they often produce intricate patterns that reflect an underlying complex physics. The observed patterns vary from coffee-rings and uniform sediments in sessile droplets [1] to complex structures [2] depending on the particle-particle and particle-surface interactions and other parameters. Here we present labyrinth-type patterns that form when the suspension is dried in strongly confined conditions and very low evaporation rates (Fig. 1; [2]) [1] R. D. Deegan et al. ‘Capillary flow as the cause of ring stains from dried liquid drops’, Nature 389, 827-829 (1997). [2] I. Beechey-Newman,N. Kizilova,A.A. Hennig,E.G. Flekkøy, & E. Eiser, Confined colloidal droplets dry to form circular mazes, Proc. Natl. Acad. Sci. U.S.A. 122 (32) e2508363122, (2025).

• Hennig, Andreas Andersen; Beechey-Newman, Ilaria; Kizilova, Natalya; Flekkøy, Eirik Grude & Eiser, Erika (2025). Confined Colloidal Droplets Make Circular Mazes. Fulltekst i vitenarkiv
• Moura, Marcel; Kern, Vanessa Ruth; Olsen, Pål Eivind; Carlson, Andreas; Måløy, Knut Jørgen & Flekkøy, Eirik Grude (2025). Fluidos complexos em confinamento: espalhamento em cunha e instabilidades em células de Hele-Shaw texturizadas. Fulltekst i vitenarkiv
• Reis, Paula Kozlowski Pitombeira; Moura, Marcel; Linga, Gaute; Toussaint, Renaud; Rikvold, Per Arne & Flekkøy, Eirik Grude [Vis alle 7 forfattere av denne artikkelen] (2025). Modeling Gas-Liquid Drainage in Porous Media with Network Models. Fulltekst i vitenarkiv
• Kern, Vanessa Ruth; Carlson, Andreas; Måløy, Knut Jørgen & Flekkøy, Eirik Grude (2024). Linking anomalous diffusion and rheology for a droplet spreading in a corner: A rheometer for power-law liquids. Fulltekst i vitenarkiv
• Lanza, Federico; Baldelli, Beatrice; Linga, Gaute; Barras, Fabian & Flekkøy, Eirik Grude (2024). The Cooling Instability. Fulltekst i vitenarkiv
• Lanza, Federico; Baldelli, Beatrice; Linga, Gaute; Barras, Fabian & Flekkøy, Eirik Grude (2024). Dynamic instability of a temperature-dependent viscous fluid in a Hele-Shaw cell. Fulltekst i vitenarkiv
• Moura, Marcel; Hansen, Alex; Måløy, Knut Jørgen & Flekkøy, Eirik Grude (2024). POROUS MATTER: Our sci-art adventures in Romania. Fulltekst i vitenarkiv
• Moura, Marcel; Kern, Vanessa Ruth; Carlson, Andreas; Måløy, Knut Jørgen & Flekkøy, Eirik Grude (2024). Linking anomalous diffusion and rheology for a droplet spreading in a corner: A rheometer for power-law liquids. Fulltekst i vitenarkiv
• Moura, Marcel; Måløy, Knut Jørgen; Flekkøy, Eirik Grude; Brodin, Joachim Falck; Reis, Paula Kozlowski Pitombeira & Linga, Gaute [Vis alle 7 forfattere av denne artikkelen] (2024). A pool of two-phase flows experiments: films, bursts, patterns and avalanches. Fulltekst i vitenarkiv
• Moura, Marcel; Måløy, Knut Jørgen; Flekkøy, Eirik Grude; Brodin, Joachim Falck; Reis, Paula Kozlowski Pitombeira & Linga, Gaute [Vis alle 7 forfattere av denne artikkelen] (2024). A little bit of our activity at PoreLab and Njord. Fulltekst i vitenarkiv
• Moura, Marcel; Hansen, Alex; Flekkøy, Eirik Grude & Måløy, Knut Jørgen (2024). POROUS MATTER: PoreLab's sci-art adventures in Romania. Fulltekst i vitenarkiv
• Reis, Paula Kozlowski Pitombeira; Linga, Gaute; Moura, Marcel; Rikvold, Per Arne; Toussaint, Renaud & Flekkøy, Eirik Grude [Vis alle 7 forfattere av denne artikkelen] (2024). Investigation of liquid connectivity and drainage in granular porous media. Fulltekst i vitenarkiv
• Reis, Paula Kozlowski Pitombeira; Linga, Gaute; Moura, Marcel; Rikvold, Per Arne; Toussaint, Renaud & Flekkøy, Eirik Grude [Vis alle 7 forfattere av denne artikkelen] (2024). Investigation of liquid connectivity and drainage in granular porous media. Fulltekst i vitenarkiv
• Reis, Paula Kozlowski Pitombeira; Linga, Gaute; Moura, Marcel; Rikvold, Per Arne; Toussaint, Renaud & Flekkøy, Eirik Grude [Vis alle 7 forfattere av denne artikkelen] (2024). Network modeling of corner and bulk flows during drainage in granular porous media. Fulltekst i vitenarkiv
• Lanza, Federico; Baldelli, Beatrice; Linga, Gaute; Barras, Fabian & Flekkøy, Eirik Grude (2024). Simulating finger structures that may form when a warm liquid (lava) cools and becomes more viscous during flow through a fracture. Fulltekst i vitenarkiv
• Moura, Marcel; Reis, Paula Kozlowski Pitombeira; Schäfer, Gerhard; Toussaint, Renaud; Flekkøy, Eirik Grude & Rikvold, Per Arne [Vis alle 7 forfattere av denne artikkelen] (2023). Thin film flow: fluid transport via thin liquid films in slow porous media flows. Fulltekst i vitenarkiv
• Reis, Paula Kozlowski Pitombeira; Moura, Marcel; Linga, Gaute; Rikvold, Per Arne; Flekkøy, Eirik Grude & Måløy, Knut Jørgen (2023). A simplified pore-scale model for drainage including film flow effects. Fulltekst i vitenarkiv
• Reis, Paula Kozlowski Pitombeira; Moura, Marcel; Linga, Gaute; Rikvold, Per Arne; Flekkøy, Eirik Grude & Måløy, Knut Jørgen (2023). A modified-invasion-percolation model for drainage in quasi-2D porous media. Fulltekst i vitenarkiv
• Reis, Paula Kozlowski Pitombeira; Moura, Marcel; Linga, Gaute; Rikvold, Per Arne; Flekkøy, Eirik Grude & Måløy, Knut Jørgen (2023). A simplified pore-scale model for slow drainage including film-flow effects. Fulltekst i vitenarkiv
• Reis, Paula Kozlowski Pitombeira; Moura, Marcel; Linga, Gaute; Rikvold, Per Arne; Toussaint, Renaud & Flekkøy, Eirik Grude [Vis alle 7 forfattere av denne artikkelen] (2023). Numerical analysis of drainage in porous media using network models. Fulltekst i vitenarkiv
• Cheon, Hyejeong; Kjelstrup, Signe Helene; Kizilova, Nataliya; Flekkøy, Eirik Grude; Mason, Matthew J. & Folkow, Lars (2023). Arctic seals’ intricate nose bones keep them warm in forever winters. [Journal]. Science. Fulltekst i vitenarkiv
• Cheon, Hyejeong; Kjelstrup, Signe Helene; Kizilova, Nataliya; Flekkøy, Eirik Grude; Mason, Matthew J. & Folkow, Lars (2023). Seals Stay Warm and Hydrated in the Arctic with Larger, More Convoluted Nasal Passages. [Journal]. EurekAlert!. Fulltekst i vitenarkiv
• Yan, Lifei; Golestan, Mohammad Hossein; Berg, Carl Fredrik; Zhou, Wenyu; Hassanizadeh, S. Majid & Raoof, Amir [Vis alle 7 forfattere av denne artikkelen] (2023). Microfluidic Experiments on Constrained Oil Remobilization Induced by Water Transport in the Oil Phase. I Médici, Ezequiel F. & Otero, Alejandro D. (Red.), Album of Porous Media. Springer. ISSN 9783031238000. doi: 10.1007/978-3-031-23800-0_78. Fulltekst i vitenarkiv
• Cheon, Hyejeong; Kjelstrup, Signe Helene; Kizilova, Nataliya; Flekkøy, Eirik Grude; Mason, Matthew J. & Folkow, Lars (2023). Arctic Seals Have Weird Bones in Their Noses That Help Them Stay Warm. [Journal]. New scientist (1971). Fulltekst i vitenarkiv
• Haghanihasanabadi, Reza; Gahrooei, Hamidreza Erfani; McClure, James E.; Flekkøy, Eirik Grude & Berg, Carl Fredrik (2023). Symmetrizing multiphase flow equations for improved accuracy. Fulltekst i vitenarkiv
• Haghanihasanabadi, Reza; Gahrooei, Hamidreza Erfani; McClure, James E.; Flekkøy, Eirik Grude & Berg, Carl Fredrik (2023). A color-gradient-based phase-field equation for multiphase flow. Fulltekst i vitenarkiv
• Moura, Marcel; Brodin, Joachim Falck; Måløy, Knut Jørgen; Rikvold, Per Arne; Flekkøy, Eirik Grude & Jankov, Mihailo [Vis alle 8 forfattere av denne artikkelen] (2022). Thin film flow: fluid transport and pollution spreading in porous media. Fulltekst i vitenarkiv
• Moura, Marcel; Reis, Paula Kozlowski Pitombeira; Eriksen, Fredrik Kvalheim; Turquet, Antoine Léo; Flekkøy, Eirik Grude & Toussaint, Renaud [Vis alle 8 forfattere av denne artikkelen] (2022). Complexity: “More is Different” also in porous media flows. Fulltekst i vitenarkiv
• Moura, Marcel; Vincent-Dospital, Tom Yannick Yves; Måløy, Knut Jørgen & Flekkøy, Eirik Grude (2022). Watching paint dry and the making of the non-Newtonian doughnut. Fulltekst i vitenarkiv
• Moura, Marcel; Brodin, Joachim Falck; Måløy, Knut Jørgen; Flekkøy, Eirik Grude & Rikvold, Per Arne (2022). Capillary pumping – the spreading of pollution in porous media. Fulltekst i vitenarkiv
• Moura, Marcel; Vincent-Dospital, Tom Yannick Yves; Måløy, Knut Jørgen & Flekkøy, Eirik Grude (2022). Watching paint dry and the making of the non-Newtonian doughnut. Fulltekst i vitenarkiv
• Hansen, Alex; Flekkøy, Eirik Grude; Sinha, Santanu & Slotte, Per Arne (2022). Jaynes Statistical Mechanics Applied to Multiphase Flow in Porous Media. Fulltekst i vitenarkiv
• Reis, Paula Kozlowski Pitombeira; Moura, Marcel; Måløy, Knut Jørgen; Flekkøy, Eirik Grude & Rikvold, Per Arne (2022). Pore-scale modeling of film flow effects during gas-liquid drainage. Fulltekst i vitenarkiv
• Haghanihasanabadi, Reza; Berg, Carl Fredrik & Flekkøy, Eirik Grude (2022). Extended Allen-Chan phase-field equation for ternary fluid flows and phase-change process in binary fluid flows. Fulltekst i vitenarkiv
• Moura, Marcel; Eriksen, Fredrik Kvalheim; Turquet, Antoine Leo; Flekkøy, Eirik Grude; Toussaint, Renaud & Jankov, Mihailo [Vis alle 7 forfattere av denne artikkelen] (2021). Complexity: “More is Different” also in porous media flows. Fulltekst i vitenarkiv
• Moura, Marcel; Måløy, Knut Jørgen; Flekkøy, Eirik Grude & Toussaint, Renaud (2021). Coffee is for drinking, tea is for porous media science: intermittent burst dynamics in slow drainage experiments in porous media. Fulltekst i vitenarkiv
• Måløy, Knut Jørgen; Brodin, Joachim Falck; Rikvold, Per Arne; Moura, Marcel; Toussaint, Renaud & Schaefer, Gerhard [Vis alle 7 forfattere av denne artikkelen] (2020). Drainage in porous media under influence of a gravitational field. Fulltekst i vitenarkiv
• Bedeaux, Dick; Flekkøy, Eirik Grude; Hansen, Alex; Måløy, Knut Jørgen; Kjelstrup, Signe & Torsæter, Ole (2020). Editorial: Physics of Porous Media. Frontiers in Physics. 8, s. 1–3. doi: 10.3389/fphy.2020.00003. Fulltekst i vitenarkiv
• Moura, Marcel; Måløy, Knut Jørgen; Flekkøy, Eirik Grude; Schäfer, Gerhard & Toussaint, Renaud (2020). Thin film flow: fluid transport via thin liquid films in slow porous media flows. Fulltekst i vitenarkiv
• Brodin, Joachim Falck; Måløy, Knut Jørgen; Flekkøy, Eirik Grude & Moura, Marcel Nascimento de (2025). Stable and unstable invasion in two-phase flow in three-dimensional porous media. Universitetet i Oslo. Fulltekst i vitenarkiv Vis sammendrag

  The thesis centers on three research papers [1–3], investigating the dynamics of two-phase flow in porous media using an custum built optical 3D scanner in lab experiments. We study cases where a more viscous, denser fluid is injected into a less viscous, lighter fluid from above at constant flow rates. The focus is on the transition from stabilized invasion at high flow rates to instability at lower rates, with emphasis on dynamics and structure near the transition. The first two papers examine injection from a single point source near the top of the invasion cell. Initially, the invading fluid expands spherically, occupying adjacent pores. High local velocity ensures that capillary pressure overcomes pore-throat thresholds, even in narrow passages. The front area grows as it advances and the local flow velocity at the front decreases, reducing capillary pressure. Downward protrusions gain additional capillary pressure from the hydrostatic column, favoring penetration in these regions. When the local flow rate is sufficiently low, the hydrostatic pressure build up in the protrusions is larger than the loss of viscous pressure as compared to the lagging front. At this stage, the invasion body transitions from a compact sphere to downward-extending branches, in what we label fingering. We derive a theoretical prediction for a flow-rate-dependent critical radius for this transition and compare it with experiments, finding good agreement. In the third paper, we modify the experiment to initiate invasion as a horizontal sheet, spanning the cross section of the cell. We analyze the transition to instability as a function of flow rate. A stability criterion for the fluid interface is developed based on pressure data, incorporating flow-velocity dependent two-phase permeability and the time derivative of the pressure drop. We observe that the invading fluid’s relative permeability varies with flow rate. We measure the effects of heterogeneities in the porous media caused by regions of crystalline structures with low local permeability. We label this effect pinning and derive a methodology to measure how the front geometry can be decomposed as a sum of fingering and pinning. Together, the work elucidates how multiscale disorder in porous media interacts with viscous, capillary, and gravitational forces to shape immiscible fluid interface stability and dynamics.

Se alle arbeider i NVA