A two-phase flow description of the initiation of underwater granular avalanches

2009 ◽  
Vol 633 ◽  
pp. 115-135 ◽  
Author(s):  
MICKAËL PAILHA ◽  
OLIVIER POULIQUEN
Keyword(s):  
Critical State ◽  
Two Phase Flow ◽  
Volume Fraction ◽  
State Theory ◽  
Phase Flow ◽  
Two Phase ◽  
Initial Volume ◽  
Initial Volume Fraction ◽  
Critical State Theory

A theoretical model based on a depth-averaged version of two-phase flow equations is developed to describe the initiation of underwater granular avalanches. The rheology of the granular phase is based on a shear-rate-dependent critical state theory, which combines a critical state theory proposed by Roux & Radjai (1998), and a rheological model recently proposed for immersed granular flows. Using those phenomenological constitutive equations, the model is able to describe both the dilatancy effects experienced by the granular skeleton during the initial deformations and the rheology of wet granular media when the flow is fully developed. Numerical solutions of the two-phase flow model are computed in the case of a uniform layer of granular material fully immersed in a liquid and suddenly inclined from horizontal. The predictions are quantitatively compared with experiments by Pailha, Nicolas & Pouliquen (2008), who have studied the role of the initial volume fraction on the dynamics of underwater granular avalanches. Once the rheology is calibrated using steady-state regimes, the model correctly predicts the complex transient dynamics observed in the experiments and the crucial role of the initial volume fraction. Quantitative predictions are obtained for the triggering time of the avalanche, for the acceleration of the layer and for the pore pressure.

Eulerian Two-Phase Flow Modeling of Steam Direct Contact Condensation for the Fukushima Accident Investigation

2014 ◽  
Author(s):  
Marco Pellegrini ◽  
Giulia Agostinelli ◽  
Hidetoshi Okada ◽  
Masanori Naitoh
Keyword(s):  
Two Phase Flow ◽  
Volume Fraction ◽  
Fluid Model ◽  
Fluid Dynamic ◽  
Interfacial Region ◽  
Phase Flow ◽  
Two Phase ◽  
Fukushima Accident ◽  
Average Cell Size ◽  
Average Cell

Steam condensation is characterized by a relatively large interfacial region between gas and liquid which, in computational fluid dynamic (CFD) analyses, allows the creation of a discretized domain whose average cell size is larger than the interface itself. For this reason generally one fluid model with interface tracking (e.g. volume of fluid method, VOF) is employed for its solution in CFD, since the solution of the interface requires a reasonable amount of cells, reducing the modeling efforts. However, for some particular condensation applications, requiring the computation of long transients or the steam ejected through a large number of holes, one-fluid model becomes computationally too expensive for providing engineering information, and a two-fluid model (i.e. Eulerian two-phase flow) is preferable. Eulerian two-phase flow requires the introduction of closure terms representing the interactions between the two fluids in particular, in the condensation case, drag and heat transfer. Both terms involve the description of the interaction area whose definition is different from the typical one adopted in the boiling analyses. In the present work a simple but effective formulation for the interaction area is given based on the volume fraction gradient and then applied to a validation test case of steam bubbling in various subcooling conditions. It has been shown that this method gives realistic values of bubble detachment time, bubble penetration for the cases of interest in the nuclear application and in the particular application to the Fukushima Daiichi accident.

Numerical Investigation of Two-Phase Flow Over Unglazed Plate Collector Covered With Porous Material of Wire Screen for Solar Water Heater Application

2018 ◽  
Vol 141 (3) ◽  
Author(s):  
T. Salameh ◽  
Y. Zurigat ◽  
A. Badran ◽  
C. Ghenai ◽  
M. El Haj Assad ◽  
...  
Keyword(s):  
Surface Tension ◽  
Porous Material ◽  
Water Flow ◽  
Two Phase Flow ◽  
Volume Fraction ◽  
Phase Flow ◽  
Two Phase ◽  
Solar Water ◽  
Wire Screen ◽  
Effect Of Surface

This paper presents three-dimensional numerical simulation results of the effect of surface tension on two-phase flow over unglazed collector covered with a wire screen. The homogenous model is used to simulate the flow with and without the effect of porous material of wire screen and surface tension. The Eulerian-Eulerian multiphase flow approach was used in this study. The phases are completely stratified, the interphase is well defined (free surface flow), and interphase transfer rate is very large. The liquid–solid interface, gas–liquid interface, and the volume fraction for both phases were considered as boundaries for this model. The results show that the use of porous material of wire screen will reduce the velocity of water flow and help the water flow to distribute evenly over unglazed plate collector. The possibility of forming any hot spot region on the surface was reduced. The water velocity with the effect of surface tension was found higher than the one without this effect, due to the extra momentum source added by surface tension in longitudinal direction. The use of porous material of wires assures an evenly distribution flow velocity over the inclined plate, therefore helps a net enhancement of heat transfer mechanism for unglazed solar water collector application.

scholarly journals Modeling of Two-Phase Flow in Rough-Walled Fracture Using Level Set Method

Geofluids ◽  
2017 ◽  
Vol 2017 ◽  
pp. 1-11 ◽  
Author(s):  
Yunfeng Dai ◽  
Zhifang Zhou ◽  
Jin Lin ◽  
Jiangbo Han
Keyword(s):  
Crude Oil ◽  
Level Set Method ◽  
Level Set ◽  
Two Phase Flow ◽  
Volume Fraction ◽  
Contact Angles ◽  
Immiscible Fluids ◽  
Water Volume ◽  
Phase Flow ◽  
Two Phase

To describe accurately the flow characteristic of fracture scale displacements of immiscible fluids, an incompressible two-phase (crude oil and water) flow model incorporating interfacial forces and nonzero contact angles is developed. The roughness of the two-dimensional synthetic rough-walled fractures is controlled with different fractal dimension parameters. Described by the Navier–Stokes equations, the moving interface between crude oil and water is tracked using level set method. The method accounts for differences in densities and viscosities of crude oil and water and includes the effect of interfacial force. The wettability of the rough fracture wall is taken into account by defining the contact angle and slip length. The curve of the invasion pressure-water volume fraction is generated by modeling two-phase flow during a sudden drainage. The volume fraction of water restricted in the rough-walled fracture is calculated by integrating the water volume and dividing by the total cavity volume of the fracture while the two-phase flow is quasistatic. The effect of invasion pressure of crude oil, roughness of fracture wall, and wettability of the wall on two-phase flow in rough-walled fracture is evaluated.

scholarly journals Numerical and experimental studies of gas–liquid flow and pressure drop in multiphase pump valves

2020 ◽  
Vol 103 (3) ◽  
pp. 003685042094088
Author(s):  
Yi Ma ◽  
Minjia Zhang ◽  
Huashuai Luo
Keyword(s):  
Pressure Drop ◽  
Two Phase Flow ◽  
Volume Fraction ◽  
Test System ◽  
Ball Valve ◽  
Phase Flow ◽  
Two Phase ◽  
Pressure Drops ◽  
Disk Valve ◽  
Predicted Values

A numerical and experimental study was carried out to investigate the two-phase flow fields of the typical three valves used in the multiphase pumps. Under the gas volume fraction conditions in the range of 0%–100%, the three-dimensional steady and dynamic two-phase flow characteristics, pressure drops, and their multipliers of the ball valve, cone valve, and disk valve were studied, respectively, using Eulerian–Eulerian approach and dynamic grid technique in ANSYS FLUENT. In addition, a valve test system was built to verify the simulated results by the particle image velocimetry and pressure test. The flow coefficient CQ (about 0.989) of the disk valve is greater than those of the other valves (about 0.864) under the steady flow with a high Reynolds number. The two-phase pressure drops of the three valves fluctuate in different forms with the vibration of the cores during the dynamic opening. The two-phase multipliers of the fully opened ball valve are consistent with the predicted values of the Morris model, while those of the cone valve and disk valve had the smallest differences with the predicted values of the Chisholm model. Through the comprehensive analysis of the flow performance, pressure drop, and dynamic stability of the three pump valves, the disk valve is found to be more suitable for the multiphase pumps due to its smaller axial space, resistance loss, and better flow capacity.

Water Volume Fraction Estimation in Two-Phase Flow Based on Electrical Capacitance Tomometry

2018 ◽  
Vol 18 (16) ◽  
pp. 6822-6835 ◽  
Author(s):  
Francisco R. Moreira da Mota ◽  
Daniel J. Pagano ◽  
Marina Enricone Stasiak
Keyword(s):  
Two Phase Flow ◽  
Volume Fraction ◽  
Water Volume ◽  
Phase Flow ◽  
Electrical Capacitance ◽  
Two Phase ◽  
Water Volume Fraction

scholarly journals Steam Volume Fraction in Two Phase Flow, (II)

1968 ◽  
Vol 10 (5) ◽  
pp. 238-243 ◽  
Author(s):  
Itaru MICHIYOSHI ◽  
Akimi SERIZAWA ◽  
Shinji MITANI
Keyword(s):  
Two Phase Flow ◽  
Volume Fraction ◽  
Phase Flow ◽  
Two Phase
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