scholarly journals TITAN2F: a pseudo-3-D model of 2-phase debris flows

2015 ◽  
Vol 3 (6) ◽  
pp. 3789-3822 ◽  
Author(s):  
G. Córdoba ◽  
M. F. Sheridan ◽  
E. B. Pitman
Keyword(s):  
Debris Flows ◽  
Volume Fraction ◽  
Dynamic Pressure ◽  
Solid Volume Fraction ◽  
Solid Material ◽  
Fluid Forces ◽  
Interaction Terms ◽  
Wide Range ◽  
Mass Flows ◽  
Geophysical Mass Flows

Abstract. Debris flows, avalanches, landslides, and other geophysical mass flows can contain O(106–1010) m3 or more of material. These flows commonly consist of mixture of soil and rocks with a significant quantity of interstitial fluid. They can be tens of meters deep, and their runouts can extend many kilometers. The complicated rheology of such a mixture challenges every constitutive model that can reasonably be applied; the range of length and timescales involved in such mass flows challenges the computational capabilities of existing systems.This paper extends recent efforts to develop a depth averaged "thin layer" model for geophysical mass flows that contain a mixture of solid material and fluid. Concepts from the engineering community are integrated with phenomenological findings in geo-science, resulting in a theory that accounts for the principal solid and fluid forces as well as interactions between the phases, across a wide range of solid volume fraction. A principal contribution here is to present drag and phase interaction terms that comport with the literature in geo-sciences. The program predicts the evolution of the concentration and dynamic pressure. The theory is validated with with data from one dimensional dam break solutions and it is verified with data from artificial channel experiments.

A two-fluid model for avalanche and debris flows

2005 ◽  
Vol 363 (1832) ◽  
pp. 1573-1601 ◽  
Author(s):  
E. Bruce Pitman ◽  
Long Le
Keyword(s):  
Debris Flows ◽  
Fluid Model ◽  
Solid Material ◽  
Fluid Inertia ◽  
Two Phase ◽  
Engineering Research ◽  
Mass Flows ◽  
Two Fluid Model ◽  
Two Fluid ◽  
Geophysical Mass Flows

Geophysical mass flows—debris flows, avalanches, landslides—can contain O (10 6 –10 10 ) m 3 or more of material, often a mixture of soil and rocks with a significant quantity of interstitial fluid. These flows can be tens of meters in depth and hundreds of meters in length. The range of scales and the rheology of this mixture presents significant modelling and computational challenges. This paper describes a depth-averaged ‘thin layer’ model of geophysical mass flows containing a mixture of solid material and fluid. The model is derived from a ‘two-phase’ or ‘two-fluid’ system of equations commonly used in engineering research. Phenomenological modelling and depth averaging combine to yield a tractable set of equations, a hyperbolic system that describes the motion of the two constituent phases. If the fluid inertia is small, a reduced model system that is easier to solve may be derived.

A Sharp Interface Direct Forcing Immersed Boundary Approach for Fully Resolved Simulations of Particulate Flows

2014 ◽  
Vol 136 (4) ◽  
Author(s):  
Jianming Yang ◽  
Frederick Stern
Keyword(s):  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Density Ratio ◽  
Sharp Interface ◽  
Immersed Boundary ◽  
Particulate Flows ◽  
Order Accuracy ◽  
Wide Range ◽  
Direct Forcing ◽  
Coarse Grids

In recent years, the immersed boundary method has been well received as an effective approach for the fully resolved simulations of particulate flows. Most immersed boundary approaches for numerical studies of particulate flows in the literature were based on various discrete delta functions for information transfer between the Lagrangian elements of an immersed object and the underlying Eulerian grid. These approaches have some inherent limitations that restrict their wider applications. In this paper, a sharp interface direct forcing immersed boundary approach based on the method proposed by Yang and Stern (Yang and Stern, 2012, “A Simple and Efficient Direct Forcing Immersed Boundary Framework for Fluid-Structure Interactions,” J. Comput. Phys., 231(15), pp. 5029–5061) is given for the fully resolved simulations of particulate flows. This method uses a discrete forcing approach and maintains a sharp profile of the fluid-solid interface. It is not limited to low Reynolds number flows and the immersed boundary discretization can be arbitrary or totally eliminated for particles with analytical shapes. In addition, it is not required to calculate the solid volume fraction in low density ratio problems. A strong coupling scheme is employed for the fluid-solid interaction without including the fluid solver in the predictor-corrector iterative loop. The overall algorithm is highly efficient and very attractive for simulating particulate flows with a wide range of density ratios on relatively coarse grids. Several cases are examined and the results are compared with reference data to demonstrate the simplicity and robustness of our method in particulate flow simulations. These cases include settling and buoyant particles and the interaction of two settling particles showing the kissing-drafting-tumbling phenomenon. Systematic verification studies show that our method is of second-order accuracy on very coarse grids and approaches fourth-order accuracy on finer grids.

scholarly journals Experimental analysis of particle clustering in moderately dense gas–solid flow

2021 ◽  
Vol 933 ◽  
Author(s):  
Kee Onn Fong ◽  
Filippo Coletti
Keyword(s):  
High Speed ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Stokes Number ◽  
Spherical Particles ◽  
High Speed Imaging ◽  
Dense Particle ◽  
Laboratory Observation ◽  
Laboratory Setup ◽  
Wide Range

In collisional gas–solid flows, dense particle clusters are often observed that greatly affect the transport properties of the mixture. The characterisation and prediction of this phenomenon are challenging due to limited optical access, the wide range of scales involved and the interplay of different mechanisms. Here, we consider a laboratory setup in which particles fall against upward-moving air in a square vertical duct: a classic configuration in riser reactors. The use of non-cohesive, monodispersed, spherical particles and the ability to independently vary the solid volume fraction ( $\varPhi _V = 0.1\,\% - 0.8\,\%$ ) and the bulk airflow Reynolds number ( $Re_{bulk} = 300 - 1200$ ) allows us to isolate key elements of the multiphase dynamics, providing the first laboratory observation of cluster-induced turbulence. Above a threshold $\varPhi _V$ , the system exhibits intense fluctuations of concentration and velocity, as measured by high-speed imaging via a backlighting technique which returns optically depth-averaged fields. The space–time autocorrelations reveal dense and persistent mesoscale structures falling faster than the surrounding particles and trailing long wakes. These are shown to be the statistical footprints of visually observed clusters, mostly found in the vicinity of the walls. They are identified via a percolation analysis, tracked in time, and characterised in terms of size, shape, location and velocity. Larger clusters are denser, longer-lived and have greater descent velocity. At the present particle Stokes number, the threshold $\varPhi _V \sim 0.5$ % (largely independent from $Re_{bulk}$ ) is consistent with the view that clusters appear when the typical interval between successive collisions is shorter than the particle response time.

Multiphase Particle-in-Cell Simulations of Flow in a Gas-Solid Riser

Volume 1 ◽  
2004 ◽  
Author(s):  
K. A. Williams ◽  
D. M. Snider ◽  
J. R. Torczynski ◽  
S. M. Trujillo ◽  
T. J. O’Hern
Keyword(s):  
Gas Flow ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Three Dimensional ◽  
Extensive Study ◽  
Computational Results ◽  
Particle In Cell ◽  
Large Numbers ◽  
Wide Range ◽  
Experimental Values

The commercial computational fluid dynamics (CFD) code Arena-flow is used to simulate the transient, three-dimensional flow in a gas-solid riser at Sandia National Laboratories. Arena-flow uses a multiphase particle-in-cell (MP-PIC) numerical method. The gas flow is treated in an Eulerian manner, and the particle flow is represented in a Lagrangian manner by large numbers of discrete particle clouds with distributions of particle properties. Simulations are performed using the experimental values of the gas superficial velocity and the solids mass flux in the riser. Fluid catalytic cracking (FCC) particles are investigated. The experimental and computed pressure and solid-volume-fraction distributions are compared and found to be in reasonable agreement although the experimental results exhibit more variation along the height of the riser than the computational results do. An extensive study is performed to assess the sensitivity of the computational results to a wide range of physical and numerical parameters. The computational results are seen to be robust. Thus, the uncertainties in these parameters cannot account for the differences between the experimental and computational results.

scholarly journals Natural convective flow in circular and arc cavities filled with water-cu nanofluid: a comparative study

2018 ◽  
Vol 15 (1) ◽  
pp. 37-52 ◽  
Author(s):  
Khandker Farid Uddin Ahmed ◽  
Rehena Nasrin ◽  
Md. Elias
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Volume Fraction ◽  
Pure Water ◽  
Solid Volume Fraction ◽  
Viscous Force ◽  
Wide Range ◽  
Prandtl Numbers

The fluid flow and heat transfer mechanism on steady state solutions obtained in circular and arc-square enclosures filled with water/Cu nanofluid as well as base fluid has been investigated numerically by Galerkin's weighted residual finite element procedure. The left and right boundaries of the cavities are, respectively, heated and cooled at constant temperatures, while their horizontal walls are adiabatic. Effects of buoyancy force (Rayleigh number) and viscous force (Prandtl number) with a wide range of Ra (103 - 106) and Pr (4.2 - 6.2) on heat transfer phenomenon inside cavities are observed. The fluid flow and temperature gradient are shown by streamlines and isotherms patterns. From the investigation, it is reported that the Rayleigh and Prandtl numbers are playing significant role in heat transfer rate. The variation in heat transfer is calculated in terms of average Nusselt number. Heat transfer rate is found to be higher for water/Cu nanofluid with 2% solid volume fraction than pure water. About 2.7% higher heat transfer rate is obtained for circular cavity than that of arc cavity using water/Cu nanofluid at Ra = 104 and Pr = 5.8.

Collisional particle pressure measurements in solid–liquid flows

1997 ◽  
Vol 353 ◽  
pp. 261-283 ◽  
Author(s):  
R. ZENIT ◽  
M. L. HUNT ◽  
C. E. BRENNEN
Keyword(s):  
Pressure Transducer ◽  
Volume Fraction ◽  
Particle Density ◽  
Dynamic Pressure ◽  
Solid Volume Fraction ◽  
Terminal Velocity ◽  
Particle Dynamic ◽  
Particle Collisions ◽  
Particle Pressure ◽  
Gravity Driven Flow

Experiments were conducted to measure the collisional particle pressure in both cocurrent and countercurrent flows of liquid–solid mixtures. The collisional particle pressure, or granular pressure, is the additional pressure exerted on the containing walls of a particulate system due to the particle collisions. The present experiments involve both a liquid-fluidized bed using glass, plastic or steel spheres and a vertical gravity-driven flow using glass spheres. The particle pressure was measured using a high-frequency-response flush-mounted pressure transducer. Detailed recordings were made of many different particle collisions with the active face of this transducer. The solids fraction of the flowing mixtures was measured using an impedance volume fraction meter. Results show that the magnitude of the measured particle pressure increases from low concentrations (<10% solid volume fraction), reaches a maximum for intermediate values of solid fraction (30–40%), and decreases again for more concentrated mixtures (>40%). The measured collisional particle pressure appears to scale with the particle dynamic pressure based on the particle density and terminal velocity. Results were obtained and compared for a range of particle sizes, as well as for two different test section diameters.In addition, a detailed analysis of the collisions was performed that included the probability density functions for the collision duration and collision impulse. Two distinct contributions to the collisional particle pressure were identified: one contribution from direct contact of particles with the pressure transducer, and the second one resulting from particle collisions in the bulk that are transmitted through the liquid to the pressure transducer.

Preliminary Numerical Study of Natural Convection in a Heterogeneous Horizontal Layer Heated From Below

2014 ◽  
Author(s):  
J. L. Romano ◽  
A. T. Franco ◽  
S. L. M. Junqueira ◽  
J. L. Lage
Keyword(s):  
Natural Convection ◽  
Aspect Ratio ◽  
Volume Fraction ◽  
Numerical Study ◽  
Fluid Layer ◽  
Solid Volume Fraction ◽  
Solid Material ◽  
Horizontal Layer ◽  
Thermal Conductivity Ratio ◽  
Fixed Amount

In the present preliminary study the natural convection in a horizontal fluid layer heated isothermally from below and cooled from above, and having disconnected and conducting square solid blocks uniformly distributed in a square array within it, is numerically investigated. Nondimensional steady balance equations are presented, for a Newtonian fluid, with fluid and solid properties being considered constant and uniform. Among the nondimensional parameters ruling the phenomenon, the layer Rayleigh number is set as 105 and 106, the aspect ratio of the layer varies from 1 to 8, and the fluid Prandtl number and the solid-to-fluid thermal conductivity ratio are set as unity. The focus is on the effect of increasing the number of blocks in the layer, the blocks having progressively smaller size as to maintain the solid volume-fraction inside the layer constant and equal to 26% — this is equivalent to dispersing a fixed amount of solid material in smaller and large number of solid blocks within the layer. In general, the increase in the layer aspect ratio, with all other parameters kept constant, affects the results more as Ra increases — as expected because large Ra yields stronger convection effects. The increase in the number of blocks per unit of square cell in the layer affects the flow as to hinder convection; i.e., the finer the dispersion of solid material within the layer is (as the number of blocks increases) the weaker the resulting flow.

Theoretical Analysis of Plastic Forming Process for Semi-Solid Material

2005 ◽  
Vol 488-489 ◽  
pp. 389-392 ◽  
Author(s):  
Hong Yan ◽  
Juchen Xei
Keyword(s):  
Magnesium Alloy ◽  
Upper Bound ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Normal Component ◽  
Solid Material ◽  
Tangential Component ◽  
Forming Process ◽  
Plastic Forming ◽  
Semi Solid

The plastic forming of magnesium alloy is difficult, but the semi-solid material forming is a good method solved this problem. The mechanical model of the semi-solid materials was treated as that of the continuous porous materials in the high solid volume fraction. The upper bound theory applied for semi-solid metal plastic forming process was developed. The velocity discontinuities exist not only in the tangential component but also in normal component for the kinematically admissible displacement increment filed. The latter one was responsible for a change in solid volume fraction when the material passes the discontinuity. An upper bound analytical model and theoretical method of plastic forming process for semi-solid material has been proposed. The calculating formulas of deformed power were derived. It is theoretical basement to apply further for the practice technology analysis such as the plastic forming of magnesium alloy.

YIELD STRESS OF FRACTAL AGGREGATES

Fractals ◽  
2015 ◽  
Vol 23 (03) ◽  
pp. 1550028 ◽  
Author(s):  
YUE XI ◽  
JINJIAN CHEN ◽  
YONGFU XU ◽  
FEIFEI CHU ◽  
CHUANXIN LIU
Keyword(s):  
Fractal Dimension ◽  
Yield Stress ◽  
Power Law ◽  
Volume Fraction ◽  
Solid Volume Fraction ◽  
Published Data ◽  
Proposed Model ◽  
Wide Range ◽  
The Relationship ◽  
Theory And Experiments

A model for the yield stress of aggregates is presented that incorporates fractal dimension taking into account the solid volume fraction and the aggregate diameter. The model shows the yield stress (σy) of aggregates increases with the solid volume fraction (ϕs) as a power law, and is given by [Formula: see text], where the exponent (m) is related to fractal dimension (D), and σy0 is a referenced parameter. The relationship between exponent (m) and fractal dimension is validated by published data of aggregates and represents the measured data very well, over a wide range of the solid volume fractions. The referenced parameter (σy0) is calibrated from experiments of yield stress using power law fittings. The agreement between theory and experiments supports the idea that yielding is ultimately caused by the rupture of a few interparticle bonds within aggregates. In addition, the proposed model for the yield stress of aggregates is found to match better with experiments by comparing with all models in literature.

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