Continuum Flow Research Articles

Enhanced labile carbon flow in soil-microbes-plant-atmospheric continuum in rice under elevated CO2 and temperature leads to positive climate change feed-back

Lowland rice along with wetland sequesters one third of terrestrial carbon (C) which is responsible for both positive and negative feed-back to climate change. Labile C pools are sensitive to anticipated climate change condition (elevated CO2 and temperature). Those may eventually affect the C-stock in soil-microbes-plant-atmospheric (SMPA) continuum through priming effect and could enhance positive climate change feedback. Therefore, the objectives of the study were to analysis the effect elevated CO2 on C partitioning in rice-plant parts, soil labile C pools, and methane emission; along with identify related bacterial diversities and C-fixation pathways through whole genome metagenomic approach. The labile carbon flow in SMPA continuum was estimated for 3 years in lowland rice under elevated CO2 and temperature in open top chambers (OTCs). Rice was grown under ambient CO2 (a-CO2; 390 ± 20 μmol mol−1) and elevated CO2 and temperature (e-CO2T; 550 ± 20 μmol mol−1; 2 °C above ambient) under OTCs with replications. Soil labile C pools were increased by 25.4 to 38.9%, under e-CO2T over a-CO2. In microbes, biomass C, C-fixation pathways (metagenomic analysis) and C related soil enzymes were assayed. In atmosphere, the methane emission was measured and in plant system, C in different plant- parts, photosynthetic rates, root exudates-C were estimated to quantify labile C flow. Root exudates C was increased by 31.9% and microbial biomass C was enhanced by 23.3% under e-CO2T. Primarily, 12 soil bacterial genera which were responsible for C-fixation were dominant with higher abundance reads under e-CO2T. In C-fixation, dicarboxylate hydroxybutyrate cycle pathway and reductive citric acid cycle pathway were predominant under a-CO2 and e-CO2T, respectively. The methane emission was 26.0 and 26.8% higher under e-CO2T than a-CO2 at vegetative and reproductive stage of crop, respectively. Further, we got higher biomass accumulation, photosynthetic rate and stomatal conductance of rice under e-CO2T. Therefore, these augmented labile C flows in SMPA continuum may trigger the priming of soil C stocks, and at the same time could affect the system as a whole and results a positive feedback to climate change.

Upscaling Water Flow in Composite Nanoporous Shale Matrix Using Lattice Boltzmann Method

AbstractWater flow in nanoporous structures in shale strongly depends on water‐pore wall interactions; specifically, water‐pore wall interactions may influence flow more than water‐water interactions. Because of strong water‐pore wall interactions, the models that govern flow in nanoporous structures deviate from conventional continuum flow models such as the Darcy equation. We develop a novel lattice Boltzmann model to study water flow in nanoporous structures rendered from shale samples. First, we reconstruct three‐dimensional (3‐D) stochastic digital models based on composite shale samples that include hydrophobic organic matter (OM) and hydrophilic clay minerals. In the reconstructed digital models, we use pore size/shape distributions, porosity, and mineralogy from experiments. Then we use lattice Boltzmann models to model water flow through nanoporous structures (OM and clay) of the reconstructed shale sample, and we upscale the results to a microporous structure of composite shale containing OM, clay, and interpores associated to other minerals. The results show contraction/expansion effects of pore‐throat‐pore systems in nanoporous OM weaken the hydrophobicity‐induced slippage effect on total water flow. In nanoporous clay, the swelling effect predominates and diminishes water slippage effects on water flow. The work also highlights the importance of (1) the accuracy of reconstructed 3‐D pore networks in terms of pore connectivity, shape, and tortuosity in individual systems of OM and clay and (2) the role of OM nanopores in connecting isolated micropores to total water flow through the composite shale system.

Characterisation and modeling of a pulsed molecular beam

Standard techniques used in real-time reaction dynamics experiments, namely photoionization by a pulsed laser and velocity imaging are applied to document the time dependent velocity distribution of 2-hydroxypyridine (2-HP) molecules in a pulsed beam where 2-HP is seeded in either helium or argon. The purpose is to identify features which cannot be assigned to a pure free molecular (effusive in the present case) or a pure continuum (supersonic here) flow regime. The beam is generated in a two stage expansion, where the first stage is driven by a pulsed valve. The experimental work is complemented by simulations. Two phenomena retain the attention: (i) a slow return to the effusive flow regime after the valve opening has generated an intense supersonic flow; (ii) development of a shock wave a short time after the valve opening.

Production of nitric oxide by a fragmenting bolide: An exploratory numerical study

A meteoroid's hypersonic passage through the Earth's atmosphere results in ablational and fragmentational mass loss. Potential shock waves associated with a parent object as well as its fragments can modify the surrounding atmosphere and produce a range of physico‐chemical effects. Some of the thermally driven chemical and physical processes induced by meteoroid‐fragment‐generated shock waves, such as nitric oxide (NO) production, are less understood. Any estimates of meteoric NO production depend not only on a quantifiable meteoroid population and a rate of fragmentation, with a size capable of producing high temperature flows, but also on understanding the physical properties of the meteor flows along with their thermal history. We performed an exploratory pilot numerical study using ANSYS Fluent, the computational fluid dynamics (CFD) code, to investigate the production of NO in the upper atmosphere by small meteoroids (or fragments of meteoroids after they undergo a disruption episode) in the size range from 10−2 to 1 m. Our model uses the simulation of a spherical body in the continuum flow at 70‐ and 80‐km altitude to approximate the behaviour of a small meteoroid capable of producing NO. The results presented in this exploratory study are in good agreement with previous studies.

Evaluation of a counter-flow microchannel heat exchanger performance with air-water vapor mixture to liquid water

Given its configuration and operation conditions, the performance of a counter-flow microchannel heat exchanger (MCHX) is evaluated through detailed calculations. The fluids, both liquid water and air, are considered as continuum flow flowing in microchannels. The MCHX has 59 sheets, and each sheet has 48 microchannels. The microchannels for both fluids have the same cross section of 0.8mm×1mm and same length of 200mm. Log mean temperature difference method is adopted for this evaluation. Using appropriate equations, the properties of air-water vapor mixture are calculated based on that of the two components. Given the inlet temperature for liquid water(35℃) and air (170℃),the calculated outlet temperature for both fluids are 55.5℃ and 43.3℃, respectively. The results also show that the air at the outlet is saturated. The overall heat transfer coefficient reaches 100W/m2ꞏK, which is much higher than that of conventional heat exchanger with similar fluid combinations.

Arbitrary Lagrangian-Eulerian-type discrete unified gas kinetic scheme for low-speed continuum and rarefied flow simulations with moving boundaries.

In this paper, the original discrete unified gas kinetic scheme (DUGKS) is extended to the arbitrary Lagrangian-Eulerian (ALE) framework to enable simulation of low-speed continuum and rarefied flows with moving boundaries. For the proposed ALE-type DUGKS, the mesh motion velocity is introduced in the Boltzmann-BGK equation and a remapping-free scheme is used to discretize the governing equation. Under this coupling framework, the complex rezoning and remapping phases implemented in the traditional ALE method are avoided. In some application areas, large discretization errors are introduced in the simulation if the geometric conservation law (GCL) is not guaranteed. Therefore, three GCL-compliant approaches are discussed, and a uniform flow test case is conducted to validate these schemes. Further, to illustrate the performance of the proposed method, four test cases are simulated, including the continuum flow around an oscillating circular cylinder, the continuum flow around a pitching NACA0012 airfoil, a moving piston driven by a rarefied gas, and the rarefied flow caused by a plate oscillating in the normal direction. Finally, an extended test case considering the rarefied flow over an oscillating circular cylinder is also studied, as this condition is not sufficiently researched. Consistent and good results obtained from the above test cases demonstrate the capability of the proposed ALE-type DUGKS to simulate moving boundary problems in different flow regimes.

Multiscale gas transport behavior in heterogeneous shale matrix consisting of organic and inorganic nanopores

The complicated nanoporous structure and significant heterogeneity of shale matrix make it challenging to fully understand the gas transport behavior in shale. Towards this end, herein a multiscale approach was presented via coupling molecular dynamics (MD) simulations, analytical model and pore network model (PNM). Using MD simulations, we showed that gas transport in organic nanopores manifests a typical slippage feature whereas gas slippage breaks down in inorganic nanopores, which should be attributed to “rough” potential energy surface (PES) of inorganic walls. Based on the results of MD simulations, a unified gas transport model was derived to describe gas flow behaviors in organic and inorganic pores by integrating continuum flow theory and gas-surface dynamics theory. In particular, gas transport process in heterogeneous shale matrix was performed with the help of pore network model and the influence of multiple factors on the gas permeability of shale matrix were analysed and discussed.

Analysis of Flow Characteristics and Pressure Drop for an Impinging Plate Fin Heat Sink with Elliptic Bottom Profiles

The performance of impingement air cooled plate fin heat sinks differs significantly from that of parallel flow plate fin heat sinks. The impinging flow situations at the entrance and the right-angled bends of the plate fin heat sink are quite involved. Flow characteristics of a plate fin heat sink with elliptic bottom profiles cooled by a rectangular impinging jet with different inlet widths are studied by numerical simulations. The results of pressure drop of numerical simulations and experimental results match quite well. The numerical results show that at the same flow rate, the pressure drop decreases with the increase of the impingement inlet width, and the pressure drop increases significantly with the increase of the fin height. The larger the impingement inlet width of air-cooled plate fin heat sink, the milder the pressure drop changes with velocity. Pressure drop for an impinging plate fin heat sink without elliptic bottom profiles is larger than that with elliptic bottom profiles at the same inlet width and velocity. Based on the fundamental developing laminar continuum flow theory, an improved model which is very concise and nice for quick real world approximations is proposed. Furthermore, this paper verifies the effectiveness of this simple impinging pressure drop model.

Kinetic multiscale scheme based on the discrete-velocity and lattice-Boltzmann methods

A novel hybrid computational method based on the discrete-velocity (DV) approximation, including the lattice-Boltzmann (LB) technique, is proposed. Numerical schemes for the kinetic equations are used in regions of rarefied flows, and LB schemes are employed in continuum flow zones. The schemes are written under the finite-volume (FV) formulation to achieve the flexibility of local mesh refinement. The truncated Hermite polynomial expansion is used for matching of DV and LB solutions. Special attention is paid to preserving conservation properties in the coupling algorithm. The test results obtained for the Couette flow of a rarefied gas are in excellent agreement with the benchmark solutions, mostly thanks to mesh refinement (both in the physical and velocity spaces) in the Knudsen layer.

A self-similarity mathematical model of carbon isotopic flow fractionation during shale gas desorption

The existence of nanosized pore systems differentiates isotopic gas transport inside a shale matrix from conventional continuum flow. In this study, a novel self-similarity mathematical model was developed to investigate the effects of gas flow transport (both slip flow and free molecular diffusion flow) on isotopic gas fractionation for four different shale samples (S1 and S2 from north Germany and S3 and S4 from Xiashiwan Field, Ordos Basin, China). In this model, the nonlinear permeability and diffusion coefficients were developed for the isotopologues (12CH4 and 13CH4), respectively. By selecting appropriate exponents of the pressure gradient for 12CH4 and 13CH4, respectively, the estimated isotopic methane concentration and production rate showed a good agreement with experimental data. The developed model shows that the gas concentration of the isotopologues in samples S1 and S2 increases with time following a power law. Similarly, the gas production rates of the isotopologues in samples S3 and S4 decay with time following a power law. Moreover, the exponents of the pressure gradient for the isotopologues are close to 4 for samples S1 and S2, indicating that the effect of slip flow on isotopic gas fractionation cannot be ignored. For samples S3 and S4, the exponents of the pressure gradient for the isotopologues increase with temperature rising, which shows the promotion of isotopic gas fractionation under higher heating temperatures. The slight difference between the exponents of the pressure gradient for the isotopologues for the same shale sample reveals that the isotopic gas fractionation of carbon is a slow process.

Direct simulation Monte Carlo computations and experiments on leading-edge separation in rarefied hypersonic flow

A comprehensive study of the fundamental characteristics of leading-edge separation in rarefied hypersonic flows is undertaken and its salient features are elucidated. Separation of a boundary layer undergoing strong expansion is typical in many practical hypersonic applications such as base flows of re-entry vehicles and flows over deflected control surfaces. Boundary layer growth under such conditions is influenced by effects of rarefaction and thermal non-equilibrium, thereby differing significantly from the conventional no-slip Blasius type. A leading-edge separation configuration presents a fundamental case for studying the characteristics of such a flow separation but with minimal influence from a pre-existing boundary layer. In this work, direct simulation Monte Carlo computations have been performed to investigate flow separation and reattachment in a low-density hypersonic flow over such a configuration. Distinct features of leading-edge flow, limited boundary layer growth, separation, shear layer, flow structure in the recirculation region and reattachment are all explained in detail. The fully numerical shear layer profile after separation is compared against a semi-theoretical profile, which is obtained using the numerical separation profile as the initial condition on existing theoretical concepts of shear layer analysis based on continuum flow separation. Experimental studies have been carried out to determine the surface heat flux using thin-film gauges and computations showed good agreement with the experimental data. Flow visualisation experiments using the non-intrusive planar laser-induced fluorescence technique have been performed to image the fluorescence of nitric oxide, from which velocity and rotational temperature distributions of the separated flow region are determined.

Recasting Navier–Stokes equations

Classical Navier–Stokes equations fail to describe some flows in both the compressible and incompressible configurations. In this article, we propose a new methodology based on transforming the fluid mass velocity vector field to obtain a new class of continuum models. We uncover a class of continuum models which we call the re-casted Navier–Stokes. They naturally exhibit the physics of previously proposed models by different authors to substitute the original Navier–Stokes equations. The new models unlike the conventional Navier–Stokes appear as more complete forms of mass diffusion type continuum flow equations. They also form systematically a class of thermo-mechanically consistent hydrodynamic equations via the original equations. The plane wave analysis is performed to check their linear stability under small perturbations, which confirms that all re-casted models are spatially and temporally stable like their classical counterpart. We then use the Rayleigh-Brillouin scattering experiments to demonstrate that the re-casted equations may be better suited for explaining some of the experimental data where original Navier–Stokes equations fail.

Unified gas-kinetic wave-particle methods I: Continuum and rarefied gas flow

The unified gas-kinetic scheme (UGKS) provides a framework for simulating multiscale transport with the updates of both gas distribution function and macroscopic flow variables on the cell size and time step scales. The multiscale dynamics in UGKS is achieved through the coupled particle transport and collision in the particle evolution process within a time step. In this paper, under the UGKS framework, we propose an efficient multiscale unified gas-kinetic wave-particle (UGKWP) method. The gas dynamics in UGKWP method is described by the individual particle movement coupled with the evolution of the probability density function (PDF). During a time step, the trajectories of simulation particles are tracked until collision happens, and the post-collision particles are evolved collectively through the evolution of the corresponding distribution function. The evolution of simulation particles and distribution function is guided by the evolution of macroscopic variables, and guarantees the conservation of the scheme in the final wave-particle formulation. A new concept of multiscale multi-efficiency preserving (MMP) method is introduced. Multiscale preserving means UGKWP method preserves the flow regime from collisionless regime to hydrodynamic regime without requiring the cell size and time step to be less than the mean free path and collision time. Multi-efficiency preserving means the computational cost of the scheme including the computational time and memory cost is on the same level as the most efficient method in the corresponding regime, such as the particle methods in the rarefied regime and hydrodynamic solvers in continuum regime. The UGKWP method is shown to satisfy the MMP requirement. The UGKWP method is specially efficient for hypersonic flow simulation in all regimes in comparison with the discrete ordinate methods, and presents a much lower stochastic noise in the continuum flow regime in comparison with the particle-based Monte Carlo methods. Numerical tests for flows over a wide range of Mach and Knudsen numbers are presented. The examples include the hypersonic flow passing a circular cylinder at Mach numbers 20 and 30 and Knudsen numbers 1 and 10−4, low speed lid-driven cavity flow, laminar boundary layer, shock structure, and shock tube problems. These results validate the accuracy, efficiency, and multiscale and multi-efficiency property of UGKWP method.

A unified stochastic particle Bhatnagar-Gross-Krook method for multiscale gas flows

The stochastic particle method based on Bhatnagar-Gross-Krook (BGK) or ellipsoidal statistical BGK (ESBGK) model approximates the pairwise collisions in the Boltzmann equation using a relaxation process. Therefore, it is more efficient to simulate gas flows at small Knudsen numbers than the counterparts based on the original Boltzmann equation, such as the Direct Simulation Monte Carlo (DSMC) method. However, the traditional stochastic particle BGK method decouples the molecular motions and collisions in analogy to the DSMC method, and hence its transport properties deviate from physical values as the time step size increases. This defect significantly affects its computational accuracy and efficiency for the simulation of multiscale flows, especially when the transport processes in the continuum regime is important. In the present paper, we propose a unified stochastic particle ESBGK (USP-ESBGK) method by combining the molecular convection and collision effects. In the continuum regime, the proposed method can be applied using large temporal-spatial discretization and approaches to the Navier-Stokes solutions with second-order accuracy. Furthermore, it is capable to simulate both the small scale non-equilibrium flows and large scale continuum flows within a unified framework efficiently and accurately. The applications of USP-ESBGK method to a variety of benchmark problems, including Couette flow, thermal Couette flow, Poiseuille flow, Sod tube flow, cavity flow, Taylor-Green vortex, and flow through a slit, demonstrated that it is a promising tool to simulate multiscale gas flows ranging from rarefied to continuum regime.

Direct simulation Monte Carlo on petaflop supercomputers and beyond

The gold-standard definition of the Direct Simulation Monte Carlo (DSMC) method is given in the 1994 book by Bird [Molecular Gas Dynamics and the Direct Simulation of Gas Flows (Clarendon Press, Oxford, UK, 1994)], which refined his pioneering earlier papers in which he first formulated the method. In the intervening 25 years, DSMC has become the method of choice for modeling rarefied gas dynamics in a variety of scenarios. The chief barrier to applying DSMC to more dense or even continuum flows is its computational expense compared to continuum computational fluid dynamics methods. The dramatic (nearly billion-fold) increase in speed of the largest supercomputers over the last 30 years has thus been a key enabling factor in using DSMC to model a richer variety of flows, due to the method’s inherent parallelism. We have developed the open-source SPARTA DSMC code with the goal of running DSMC efficiently on the largest machines, both current and future. It is largely an implementation of Bird’s 1994 formulation. Here, we describe algorithms used in SPARTA to enable DSMC to operate in parallel at the scale of many billions of particles or grid cells, or with billions of surface elements. We give a few examples of the kinds of fundamental physics questions and engineering applications that DSMC can address at these scales.

On the Hydrodynamic Stability of a Lennard-Jones Molecular Fluid

As a central concept in fluid dynamics stability is fundamental in understanding transitions from laminar to turbulent flow. In continuum flows, it is well-established that a transition to turbulence can occur at subcritical Reynolds numbers, in contrast to theoretical predictions. In non-equilibrium molecular dynamics (NEMD), it has been widely observed that at a critical Reynolds number the fluid undergoes an ordering transition from an amorphous phase to a ‘string’ phase. Using the fluctuation theorem (FT) and the dissipation function, we generalize the classical continuum Reynolds-Orr equation to sheared molecular fluids by ascribing a natural description to the nature of stochastic perturbations, i.e. fluctuations in shear stress. Via the Poincare inequality, we arrive at a new stability criterion by providing a lower bound on the exponential decay of perturbations, which reduces to the classical continuum result in the limit of infinite system size. We investigate the nature of these velocity perturbations and conditions necessary for growth in the kinetic energy of perturbations. We obtain a fluid dependent estimate for the critical Reynolds number by which one may estimate the critical Reynolds number at which the fluid transitions to the string phase, thus providing a framework for generalizing classical continuum theories to the microscale.

Hypersonic aerodynamics of a deformed aeroshell in continuum and near-continuum regimes

The flexible inflatable aeroshell naturally deforms under aerodynamic loads during atmospheric entry. In this paper, we investigate the hypersonic aerodynamics of an inflatable aeroshell forebody with undulated surface deformation in the continuum and near-continuum flow regimes, where flow physics is complex involving rarefaction and thermochemical nonequilibrium effect. The aeroshell forebody shape is originated from a model of 8.3 m diameter stacked-tori hypersonic inflatable aerodynamic decelerator, and a series of surface deflections is generated by a parametric method based on the consistency of undulation with underlying structure. The trajectory points of 90, 80, and 68 km altitudes in a low Earth orbit reentry are considered. The thermochemical nonequilibrium Navier-Stokes equations with slip and no-slip boundary conditions are numerically solved to characterize flowfields and provide aerodynamic predictions. The results demonstrate that the undulated surface deflection induces local fluctuations of pressure and local Knudsen number, while the local variations of aerodynamic quantities create minor difference in total drag. The surface friction and drag are dependent on boundary conditions, i.e., either slip or no-slip model. The results also indicate that it is required to employ slip boundary conditions for the accurate prediction of friction and drag in the near continuum regime.

An improved three-dimensional implicit discrete velocity method on unstructured meshes for all Knudsen number flows

In this work, an improved implicit discrete velocity method (DVM) on unstructured meshes is developed for simulation of three-dimensional (3D) flows in all flow regimes. Different from the conventional DVM, in which only the kinetic governing equation (i.e., Boltzmann equation) is resolved in each time step, both the kinetic and macroscopic governing equations are solved simultaneously in the present method. On one hand, the solution of macroscopic governing equation yields the predicted equilibrium distribution function at cell center, which enables the fully implicit discretization of the collision term in solving the Shakhov-model kinetic equation. On the other hand, the collisional effect at the cell interface can be incorporated into the evaluation of numerical flux through the solution process of macroscopic governing equation. Thanks to these two improvements, the developed scheme can effectively overcome the defects of low efficiency and poor accuracy of the conventional semi-implicit DVM in the continuum flow regime. In addition, for practical applications of flow problems with complicated geometry, in the present work, the unstructured mesh-based solver is developed. The accuracy, efficiency, stability and flexibility of the developed solver are demonstrated by its application to simulate pipe flow, lid-driven cavity flow and supersonic flow around a blunt body.

Unified gas-kinetic wave-particle methods. II. Multiscale simulation on unstructured mesh

In this paper, we present a unified gas-kinetic wave-particle (UGKWP) method on unstructured mesh for the multiscale simulation of continuum and rarefied flow. Inheriting from the multiscale transport in the unified gas-kinetic scheme (UGKS), the integral solution of the kinetic model equation is employed in the construction of the UGKWP method to model the flow physics on the scales of cell size and time step. A novel wave-particle adaptive formulation is introduced in the UGKWP method to describe the flow dynamics in each control volume. The local gas evolution is constructed through the dynamical interaction of the deterministic hydrodynamic wave and the stochastic kinetic particle. To model the gas dynamics on the scales of cell size and time step, the decomposition, interaction, and evolution of the hydrodynamic wave and the kinetic particle depend on the ratio of time step to local collision time. In the rarefied flow regime, the UGKWP method recovers the nonequilibrium flow physics by discrete particles and performs as a stochastic particle method. In the continuum flow regime, the UGKWP method captures the flow behavior solely by macroscopic variable evolution and becomes a gas-kinetic hydrodynamic flow solver, the same as the gas-kinetic scheme, for viscous and heat-conducting Navier–Stokes solutions. In the transition regime, both kinetic particle and hydrodynamic wave contribute adaptively in the UGKWP to capture the peculiar nonequilibrium flow physics in a most efficient way. In different flow regimes, the Sod shock tube, lid-driven cavity flow, laminar boundary layer, and high-speed flow around a circular cylinder are computed to validate the UGKWP method on unstructured mesh. The UGKWP method obtains the same UGKS solutions in all Knudsen regimes. However, with an automatic wave-particle decomposition, the UGKWP method becomes very efficient. For example, at Mach number 30 and Knudsen number 0.1, the UGKWP has several-order-of-magnitude reductions in computational cost and memory requirement in comparison with UGKS. Overall, the UGKWP can capture the gas dynamics in all flow regimes efficiently and accurately from the free molecular transport to the Navier-Stokes flow evolution.

In-situ pore-scale imaging and image-based modelling of capillary trapping for geological storage of CO2

We describe an imaging and pore-scale modelling study of capillary trapping in the Paaratte Sandstone formation in the Otway Basin, Australia. Three-dimensional X-ray computed tomography (micro-CT) was used to characterize the pore structure of the reservoir core. We obtain in-situ pore-scale images of the distribution of CO2:brine analogue fluid pairs (octane:brine) within reservoir samples during low capillary number drainage and imbibition flooding experiments. The images were recorded using time-lapse X-ray micro-tomography at elevated pressure. The observed two-phase fluid distributions are consistent with a water wet system. The micro-CT images are used directly as input to a geometrically accurate quasi-static pore-scale simulation model. The validity of the quasi-static assumption is investigated by comparing on a pore-by-pore basis the simulated and imaged fluid distributions. The pore filling states are in good agreement both for drainage and imbibition displacements and the computed capillary trapping curve agrees with experimental data. This indicate that quasi-static pore-scale physics can be used to obtain averaged or continuum flow properties for low capillary number displacements. We perform a sensitivity study of the impact of the advancing contact angle on capillary trapping. The magnitude of residual trapping increases with decreasing contact angle. Land's trapping coefficient increases with increasing contact angle. We compute capillary pressure and relative permeability scanning curves. Simulated relative permeability hysteresis is compared with that predicted by the industry-standard Carlson's and Killough's models. Killough's model reproduces the simulated data more accurately.