In this paper, an Eulerian two-phase flow model, sedFoam, is extended to include an air phase together with its water and sediment phases. The numerical model called sedInterFoam is implemented using the open-source library OpenFOAM. sedInterFoam includes the previous features of sedFoam for sediment transport modeling and also solves the air–water interface using the volume-of-fluid method coupled with the waves2Foam toolbox for free-surface wave generation and absorption. Using sedInterFoam, four test cases are successfully reproduced to validate the free-surface evolution algorithm's implementation, mass conservation of sediment and fluid phases, and predictive capabilities and to demonstrate its potential in modeling a broader range of coastal applications with sediment transport dominated by surface waves.

AbstractDespite growing evidence suggesting chemically distinct regions and partial melting at the core-mantle boundary (CMB) throughout Earth’s history, current heat-flow models assume a homogeneous thermal boundary layer. To understand probable thermal response of bridgmanite to subducted slab, we measured thermal diffusivity of mid-ocean ridge basalt (MORB)-bearing olivine polycrystalline as an analogy. Our results show a sharp increase of thermal conductivity with an addition of 0.1 vol. % MORB, followed by a systematic decrease with increasing MORB. When the infection point of 1.2–5 vol.% is exceeded, thermal conductivity jump again with 10 vol.% MORB. If it were the case at the CMB, MORB introduced by subducted slab and scattered by mantle flow may have led to lateral variation of heat flux. It results in plume clusters with varying scales, which either grows into superplume with mobile plume root or vanishes when MORB is drained to the infection point.

In this paper, we present a new design for a 1 atm gas-mixing furnace using the gas mixture CO–CO2–SO2. This furnace can simulate disequilibrium processes such as magmatic and volcanic degassing. Here, we present the technical aspects of the design. The furnace can sustain temperatures of up to 1650 ∘C and has a hot zone that spans 200 mm vertically, where the hotspot is determined to be ∼ 32 mm below the midpoint of the furnace enclosure. The four mass flow controllers are individually calibrated and accurate to within 0.8 % of the specified value. The fO2 is accurately reproduced in the furnace within ±0.002 log units, as calibrated by the Fe–FeO reaction across the iron–wüstite (IW) buffer at 1300 ∘C. The furnace can reliably simulate dynamic conditions, where the fO2 can be modulated at a maximum rate of 2.0 log units min−1 by varying the gas mixture. A delay of 40 s is observed to attain the fO2 calculated from the gas mixture, at the hotspot. A series of safety measures to protect the user from exposure to the toxic gases are detailed. In our experiments, the furnace is used to determine sulfur isotope fractionation factors among melt, sulfide, and the gas phase, within a magmatic context, using either crystals of olivine or silica glass tubes. The furnace has the potential to investigate various other dynamic high-temperature reactions occurring on Earth.

The capability of an Eulerian two-phase model, SedFoam, in simulating the onset of scour underneath a pipeline and the backfill process is investigated. When a pipeline is slightly buried in the sediment bed, the scour onset can be caused by the piping process, which is due to seepage flow moving underneath the pipeline driven by the upstream–downstream pressure difference. To directly resolve piping as part of the scour simulation has been a challenge in the single-phase models. Alternatively, the two-phase models may be capable of simulating piping and backfill as it can resolve the interactions between the flow, structure, sediment transport, and seepage flow using a single set of governing equations and closures. To prove this point, SedFoam is validated by two laboratory experiments for the onset of scour underneath a pipeline. For piping driven by a prescribed upstream–downstream pressure difference, the model captures the temporal evolution of the pore-pressure gradient and the resulting fine-scale bathymetric change around the pipe consistent with the measured data. The model further provides insight into the seepage flow and the creeping movement of sediments during the onset of scour. When simulating piping driven by a unidirectional current, SedFoam successfully predicts piping driven by the upstream–downstream pressure gradient due to the incoming flow deceleration by the presence of pipeline and flow separation. As a proof-of-concept application, SedFoam is applied to simulate pipeline scour driven by an oscillatory flow. Although the boundary layer streaming effect is neglected, the model result shows realistic scour onset and the development of a scour hole. To demonstrate the model's capability to simulate the backfill process, the pipeline is then lowered artificially into the scour hole as an idealized treatment of the complex pipeline sinking process during scour. The resulting burial depth due to backfill is similar to that predicted by the empirical formula.

Melting properties of the deep mantle remain controversial due to experimental difficulties; e.g., reports of solidus temperatures of mantle-relevant compositions span over similar to 700K at 2000 km depth. This situation limits our understanding of the thermochemical state of the Earth's interior. Using the laser heated diamond anvil cell (LH-DAC), we performed new experimental determination of the solidus profile of ultra-dry pyrolite and the solidus of two compositions of (Mg,Fe)(Si,Al)O-3 bridgmanite (Bg). Melting was detected (i) from -the correlation between laser power and sample temperature, -changes of sample texture and -the level of visible light absorption, for all samples, (ii) using X-ray diffraction, for the MgSiO3 composition and (iii) after scanning electron microscope observations, for selected Fe-bearing samples. Special care was given to using ultra-dry experimental chambers and to determination of sample temperature. In particular, we discuss the wavelength-dependent thermal emission of silicate samples, which lowers the solidus by 100 to 300 K, compared to the grey-body assumption. The solidus of MgSiO3-Bg is in good agreement with previous reports using ab initio calculations and shock wave experiments. We observe a net decrease in the solid-liquid Clapeyron slope at 60(3) GPa and 4400(200) K, which can be related to rapid pressure-induced coordination change of Si in the melt. (Mg-0.955,Fe-0.045)(Si-0.993,Al-0.007)O-3 Bg melts 600-800K lower than MgSiO3-Bg. Its solidus evolves smoothly with pressure, suggesting progressive Si coordination change in the melt. In the pressure range investigated (24-135GPa) Clapeyron slopes suggest rapid decrease of the volume of fusion, from 14 to 2% for MgSiO3 and from 9 to 3% for (Fe,Al)-bearing Bg, assuming congruent melting. By comparing the solidii of various silicates, it appears that the higher the number of cations, the less pronounced is the curvature of the solidus. This observation suggests that the relatively ordered structure of simple liquid compositions with a limited number of distinct network-modifying cations frustrates the coexistence of tetrahedrally and octahedrally coordinated Si polyhedral. The solidus of pyrolite presents a smooth evolution from 2200(100) K to 3950(200) K in the same pressure interval. This is very similar to our previous work on chondritic-type mantle. The new solidus is 200-300 K lower than that of KLB-1 peridotite, which can be related to more incompatible elements in pyrolite. It remains problematic that our solidus plots several 100 K higher than other recent measurements performed on pyrolite; we discuss the possibility of a higher water content in previous samples, compared to our experiments. Assuming a dry lowermost mantle, our results imply a core-mantle boundary temperature lower than 3950(200) K. Modeling the melting diagram at the core-mantle boundary suggests a pseudo-eutectic melt significantly depleted in SiO2, compared to the composition of the mean mantle. (c) 2022 Elsevier B.V. All rights reserved.

In this paper, two-phase flow simulations of oscillatory sheet flow experimental configurations involving medium and fine sand using a turbulence-resolving two-fluid model are presented. The turbulence-resolving two-phase flow model reproduces the differences of behaviour observed between medium and fine sand whereas turbulence-averaged models require an almost systematic tuning of empirical model coefficients for turbulence–particle interactions. The two-fluid model explicitly resolves these interactions and can be used to study in detail the differences observed experimentally. Detailed analysis of concentration profiles, flow hydrodynamics, turbulent statistics and vertical mass balance allowed the confirmation that unsteady effects, namely phase-lag effect and enhanced boundary layer thickness, for fine sand are not only due to the small settling velocity of the particles relative to the wave period. The occurrence and intensity of unsteady effects are also affected by a complex interplay between flow instabilities, strong solid-phase Reynolds stress and turbulence attenuation caused by the presence of the particles.

In this paper the capabilities of the turbulence-resolving Eulerian-Eulerian two-phase flow model to predict the suspension of mono-dispersed finite-sized solid particles in a boundary layer flow are investigated. For heavier-than-fluid particles, having settling velocity of the order of the bed friction velocity, the two-fluid model significantly under-estimates the turbulent dispersion of particles. It is hypothesized that finite-size effects are important and a correction model for the drag law is proposed. This model is based on the assumption that the turbulent flow scales larger than the particle diameter will contribute to the resolved relative velocity between the two phases, whereas eddies smaller than the particle diameter will have two effects: (i) they will reduce the particle response time by adding a sub-particle scale eddy viscosity to the drag coefficient, and (ii) they will contribute to increase the production of granular temperature. Integrating finite-size effects allows us to quantitatively predict the concentration profile for heavier-than-fluid particles without any tuning parameter. The proposed modification of the two-fluid model extends its range of applicability to tackle particles having a size belonging to the inertial range of turbulence and allows us to envision more complex applications in terms of flow forcing conditions, i.e. sheet flow, wave-driven transport, turbidity currents and/or flow geometries, i.e. ripples, dunes, scour.

This paper presents a numerical investigation of the scour phenomenon around a submarine pipeline. The numerical simulations are performed using SedFoam, a two-phase flow model for sediment transport implemented in the open source Computational Fluid Dynamics (CFD) toolbox OpenFOAM. The paper focuses on the sensitivity of the granular stress model and the turbulence model with respect to the predictive capability of the two-phase flow model. The quality of the simulation results is estimated using a statistical estimator: the Brier Skill Score. The numerical results show no sensitivity to the granular stress model. However, the results strongly depend on the choice of the turbulence model, especially through the different implementations of the cross-diffusion term in the dissipation equation between the k − ε and the k − ω 2006 models. The influence of the cross-diffusion term tends to indicate that the sediment transport layer behaves more as a shear layer than as a boundary layer, for which the k − ε model is more suitable.

(1) LEGI, Grenoble Alpes, Grenoble INP, CNRS, 38000 Grenoble, France (julien.chauchat@univ-grenoble-alpes.fr), (2) IMFT, Université de Toulouse; INPT, UPS; Toulouse, France, (3) Applied Ocean Physics & Engineering, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA, (4) Center for Applied Coastal Research, University of Delaware, Newark, DE 19716, USA., (5) Dept. of Civil and Environmental Eng., Pennsylvania State Univ., State College, PA 16802, USA.

Scour around structures is a major engineering issue that requires a detailed description of the flow field as well as sediment transport processes. Due to enhanced suspended load associated with vortices generated around structures, sediment transport cannot be solely related to bed shear stress, such as Shields parameter based formula. In order to address this issue, we used a multi-dimensional two-phase flow solver, sedFoam-2.0 (Chauchat et al., GMD 2017) implemented under the open-source CFD toolbox OpenFOAM. Three configurations are studied and compared with experimental and numerical data from the literature. First, the 2D configurations of an horizontal cylinder lying on a sediment bed (Mao, 1986; Sumer et al., 2001) are investigated. Then, the 3D configuration of the scour around a vertical cylindrical pile reported by Roulund et al. (2005) for rigid-bed and live bed cases is investigated.

In this paper, the application of a two-phase flow model to scour processes is presented. The model is first calibrated against experimental data of unidirectional sheet-flow (one-dimensional configuration). The model is then applied to multi-dimensional configurations for the scour under a submarine pipeline and around a vertical pile. The results show that quantitative results can be obtained at the upstream sides of structures, the lee-wake erosion driven by the vortex shedding deserves further research.