One-phase Flow Research Articles

2-PHASE FLOW ANALYSIS OF TSUNAMI FORCES ACTING ON BRIDGE STRUCTURES

The understanding of interactions between tsunami and structure is very important to consider tsunami countermeasures, though the interaction includes complex phenomena. For example, two-phase flow can be found when the tsunami hits a bridge structure with entrapping air beneath it. The air sometimes affects forces acting on the bridge, and the effect of entrapped air has to be taken into account to investigate the tsunami forces. This study is intended to investigate the tsunami forces acting on the bridge with using two-phase flow model. Three bridge models were tested in this study, where the slab bridge without girders beneath it, the slab with two girders, and the slab with three girders. The simulation results were compared with the results obtained from one-phase flow simulation, and also verified with experimental ones. This study revealed that, in the investigation of tsunami forces acting on the slab bridge without girder, the results of both one-phase simulation and two-phase one agree well with experimental results. In the simulation on the slab bridge with girders, the results from two-phase simulation correlate better with experimental results in comparison with the results from one-phase simulation. Furthermore, the entrapped air between girders highly affects the characteristic of uplift force.

Numerical simulation of three-dimensional breaking waves on a gravel slope using a two-phase flow Navier–Stokes model

Wave breaking is mainly a three-dimensional flow problem characterized by wave energy dissipation due to turbulence. The understanding of the wave breaking mechanism on a beach is essential in studying coastal processes. The complexity of the wave-induced turbulence flow is also increased by the presence of a two-phase flow, which introduces buoyancy effects. In this work a set of numerical experiments is carried out on wave breaking on a gravel slope. The influence of a one-phase and two-phase flow and the permeability effect of the beach are investigated numerically by means of a Navier–Stokes model known as IH-3VOF, which considers the volume-averaged Reynolds-averaged Navier–Stokes (VARANS) equations (del Jesus, 2011 [3]) to characterize the flow within the porous media. The accuracy of the VARANS equations is demonstrated by means of comparisons with laboratory data. The results are found to be within a 2% error in terms of wave height prior to the broken wave, and up to a 10% error after then, and in the order of 0.20 s in the time domain for the worst case. A further analysis of wave evolution on a permeable beach with alongshore variation of porosity is studied. Three-dimensional wave breaking and post-breaking wave transformations alongshore are analysed according to porosity values.

Numerical scheme for coupling two-phase compositional porous-media flow and one-phase compositional free flow

Numerical scheme for coupling two-phase compositional porous-media flow and one-phase compositional free flow

Multi-scale simulation of paperboard edge wicking using a fiber-resolving virtual paper model

When liquid packaging board is made aseptic in the filling machine, the unsealed edges of the board are exposed to hydrogen peroxide. A high level of liquid penetration may lead to aesthetic as well as functional defects. The ability to make a priori predictions about the edge wicking properties of a certain paperboard material is therefore of great interest to the paper industry, as well as to packaging manufacturers. In this paper, a multi-scale framework is proposed that allows for detailed simulation of the edge wicking process. On the fiber micro-scale, virtual paper models are generated based on input from tomographic and scanning electron microscope (SEM) images. A pore morphology method is used to calculate capillary pressure curves, and on the active pores, one-phase flow simulations are performed for relative permeabilities. The results as functions of saturation and porosity are stored in a database. The database is used as input for two-phase flow simulations on the paper macro-scale. The resulting fluid penetration is validated against pressurized edge wick measurements on paper lab sheets with very good agreement. The proposed multi-scale approach can be used to increase the understanding of how edge wicking in paperboard packages depends on the micro-structure.

A Limiter for Preventing Singularity in Simplified Finite Volume Methods

AbstractSystem simulation with equation based and object-oriented modelling languages has become an important tool for system and control design of vapour compression cycles. A common approach of modelling one-phase and two-phase fluid flow is 1-D spatial discretisation according to the Finite Volume Method. In order to avoid stiff systems and to speed up simulation, pressure loss and momentum balance are usually handled in a simplified way. There exist different approaches. But all approaches suffer from one drawback. There are points where the resulting set of equations is not solvable and simulation fails. In this contribution the solvability problem is analysed in detail. It is shown that these problems are closely connected to fluid properties. Based on this result a modelling approach is suggested to avoid singularities.

Experimental measurement and numerical modeling of cavitating flow in converging-diverging nozzle

Paper presents results of the experimental research and computational modeling aimed on cavitating vortical structures induced by swirling flow. An experimental circuit was built with swirl generator and converging-diverging nozzle made of plexiglass. Cavitating zone develops along the nozzle axis due to balance of pressure and centrifugal forces. Resulting vortical structure is unstable, which is manifested by pulsations. Computational modelling of the one-phase flow is carried out and results are confronted with experimental data and the different modelling approaches are discussed.

Research Analysis and Experiment Study on Flow Field of Hydrodynamic Coupling

CFD simulation and PIV test technology provide effective solution for revealing the complex flow of hydrodynamic coupling’s internal flow field. Some articles reported that the combination of CFD simulation and PIV test can be used for analyzing the internal flow field of coupling, and such analysis focuses on one-phase flow. However, most internal flow field of coupling are gas-fluid two-phase flow under the real operation conditions. In order to reflect the gas-fluid two-phase flow of coupling objectively, CFD three-dimensional numerical simulation is conducted under two typical operation conditions. In addition, modern two-dimensional PIV technology is used to test the two-phase flow. This method of combining experiments and simulation presents the characteristics of the flow field when charging ratios are different.

Grinding in an air classifier mill — Part I: Characterisation of the one-phase flow

In this and the related second paper [1], we present an in-depth study of the two-phase flow and the stressing conditions of particles in an air classifier hammer mill. This type of mill belongs to the mostly used mills at all. In order to develop a predictive grinding model not only the material's reaction to the applied stress but also the stressing conditions within the mill, e.g. impact velocity, incidence angle, number of stress events, have to be known. The latter are strongly affected by the interactions between the fluid and the solid phase within the mill. Systematic flow investigations in the vicinity of the impact elements and in the region of the internal classifier have been performed by Particle Image Velocimetry (PIV) and by numerical predictions of the fluid flow in the complete mill using a commercial CFD solver. Different pin geometries have been studied at various peripheral velocities of the grinding disk and the classifier. The classifier velocity does not influence the velocity profiles near the impact elements in the main flow direction and vice versa, the flow in the grinding zone has little influence on the classification. The velocity profile in front of the impact element, where the comminution process takes place, is constant with time and preserves a characteristic form independent of the operational conditions.

VOLUME-OF-FLUID MODEL COMFLOW SIMULATIONS OF WAVE IMPACTS ON A DIKE

ComFLOW is a 3D Volume-of-Fluid (VOF) model to solve the incompressible Navier-Stokes equations including free surface, or to solve the Navier-Stokes equations for two-phase flow problems (two-phase flow: both an incompressible viscous fluid (e.g., water) and a compressible viscous fluid (e.g., air) are present). The problem statement of the present study reads: 'Is ComFLOW capable of accurate prediction of wave impacts on (impermeable) coastal structures such as dikes? And, if so, what are the preferred model settings and associated computing times?'. In this paper, ComFLOW is validated for this purpose by comparison against pressure data as measured in the Delta flume by pressure sensors at dikes. We have selected three different experiments, with typical dike geometries (slope 1:3.5, with and without berm) at which more than 20 pressure sensors were installed. The results can be summarized as follows. The pressure measurements are reproduced well in the simulations. A grid with about 170 grid cells per wave length in the horizontal, and between 4 and 6 grid cells per wave height in the vertical, proves to be sufficiently fine. At such a grid resolution and with about 450 by 35 grid cells in the computational domain, a typical CPU time is 35 minutes for simulations with a model time of 10 wave periods. For the present application, it is preferable to use the one-phase flow model rather than the two-phase flow model, since the former gives better results in the lower located pressure sensors and consumes less CPU time.

Formation and Deposition of Iron Oxides on Stainless Steel and Carbon Steel in Conditions of Secondary Circuits of Pressurized Water Reactors

Abstract An experimental circulating water loop was built to follow the formation, the transport, and the deposition of iron oxides in the feedwater system of the secondary circuit of PWR plants. The test section was made from carbon steel while all other parts of the loop were made from stainless steel. Tests were performed for 18 days to 101 days in one-phase flow conditions at 150 L/h with a linear velocity between 0.92 m/s and 1.1 m/s at 220°C in an ammonia (NH3) and hydrazine (N2H4) medium. A magnetite (Fe3O4) film appeared on the surface of carbon steel tubes within a few days. Iron oxides were also present on stainless steel segments as goethite (FeOOH) at room temperature and as magnetite at 220°C. The oxide film on carbon steel was heterogeneous and its thickness varied from several μm to 40 μm, while the oxide film on stainless steel did not exceed 2 μm.

Exploratory study on the roller effect of direct hydraulic jumps

Can a direct hydraulic jump also be generated if the surface roller is substituted with a corresponding inset? This and related questions are considered in the note, to understand the role of the roller. Based on recent findings relating to the classical hydraulic jump, its modification using bottom and surface insets is reconsidered using laboratory experimentation. The results of these tests are reported below using mainly photography and basic hydraulic computations. It is further demonstrated that the roller may not be separated from the hydraulic jump in a free surface arrangement. This would greatly simplify observations, because the standard two-phase flow including an air–water mixture flow would become a one-phase flow consisting of only water flow. The implications of this result are discussed. This work has exploratory character and should stimulate a further discussion on the main flow features of direct hydraulic jumps.

In situ optical monitoring of the solution concentration influence on supercritical particle precipitation

We report a novel approach for the measurement of the location of particle formation in the supercritical antisolvent process (SAS). The measurement strategy is based on in situ Raman and elastic light scattering. In the SAS process, paracetamol was used as the solute, ethanol as the solvent and carbon dioxide as the antisolvent. Experiments were performed under miscible conditions for the binary system ethanol and carbon dioxide at 313 K and pressures between 10 MPa and 17.5 MPa. For high paracetamol concentrations in the injected ethanol solution, particles were found to start precipitating after jet breakup in a multi-phase flow. For low paracetamol concentrations, precipitation starts later in a one-phase flow, when the transient interface (phase boundary) between the injected solution and the supercritical carbon dioxide has diminished.

Model-Based Monitoring and Leak Detection in Oil and Gas Pipelines

Summary An adaptive Luenberger-type estimator for the purpose of monitoring flow conditions and locating and quantifying leakages in petroleum pipelines is presented. The estimator only needs measurements of velocity, pressure, and temperature at the inlet and velocity and pressure at the outlet to function. The measurements are used to form a special set of boundary conditions for the estimator that ensures fast convergence of the estimation error. Depending only on measurements from inlet and outlet makes it possible to use OLGA, which is a state-of-the-art computational fluid dynamics simulator, to govern the one-phase fluid flow of the estimator. The estimator is tested with both a straight, horizontal pipeline and an actual, long pipeline with inclinations, and both simulations with oil and gas are carried out. In order to cope with modeling errors and biased measurements, estimation of roughness in the monitored pipeline is introduced.

Predictions of turbulent flow and heat transfer in gas–droplets flow downstream of a sudden pipe expansion

Droplets-laden turbulent flow downstream of a sudden pipe expansion has been investigated by using Euler/Euler two-fluid model for the gaseous and dispersed phases. Significant increase of heat transfer in separated flow at the adding of evaporating droplets has been demonstrated (more than 2 times compare with one-phase flow at the value of mass concentration of droplets M L 1 ⩽ 0.05). Addition of dispersed phase to the turbulent gas flow results in insignificant increase of the reattachment length. Low-inertia droplets ( d 1 ⩽ 50 μm) are well entrained into the circulation flow and present over the whole pipe section. Large particles ( d 1 ≈ 100 μm) go through the shear layer not getting into the detached area. Comparison with experimental data on separated gas–droplets flows behind the plane backward-facing step has been carried out.

Experimental characterization of single and two-phase flow through nickel foams

Abstract Experimental tests are performed to determine the hydraulics parameters, which characterize one-phase (air) and two-phase flow (air and water) in thin metallic foams (thickness of the order of 1.5 mm). Three types of nickel foams produced by INCO and RECEMAT are considered. The specific experimental set-up allows the study of low in-situ compression effects on the foam sample. Regarding one-phase flow, intrinsic permeability and inertial coefficient (also named passability) are determined from a semi-analytical solution of the Darcy–Forchheimer–Brinkman equation, whereas concerning two-phase flow only gas phase relative properties are estimated through the generalized Darcy–Forchheimer equation. For the used experimental flow range, the results which are in line with former studies show the importance of the inertial effects. The in-situ foam compression and tightening effects lead to higher permeability and passability values, knowing that permeability coefficient is determined with a better accuracy than the inertial coefficient.

Equivalent block transmissivity in an irregular 2D polygonal grid for one-phase flow: A sensitivity analysis

Upscaling is needed to transform the representation of non-additive space-dependent variables, such as permeability, from the fine grid of geostatistical simulations (to simulate small-scale spatial variability) to the coarser, generally irregular grids for hydrodynamic transport codes. A new renormalisation method is proposed, based on the geometric properties of a Voronï grid. It is compared to other classic methods by a sensitivity analysis (grid, range and sill of the variogram, random realisation of a simulation); the criterion is the flux of a tracer at the outlet. The effect of the upscaling technique on the results appears to be of second order compared to the spatial discretisation, the choice of variogram, and the realisation.

Mixing in milli torus reactor under aerated conditions

The present paper contributes to improve the understanding of two-phase flow hydrodynamics characteristics in milli torus reactor. To reach this goal, experiments were performed in a vertical milli torus reactor, having a capacity of 0.140 l. The effect of the aeration numbers and the impeller rotation speeds has been studied. It was found that the homogenization of the tracer inside the gas–liquid milli torus reactor was nearly achieved after more recirculations than those obtained in one-phase flow. Under aerated conditions, the flow pattern depended on both impeller rotation speeds and aeration numbers. Two flow regimes have been distinguished: not-dispersed and dispersed flow regimes. The flow induced by a rotating marine impeller reduced bubble size and prevented bubbles coalescence for aeration numbers Fl > 0.0021, at which the dispersed flow regime can be maintained in the milli torus reactor. The flow behaviour inside the milli torus reactor was modelled by the dispersed plug flow model. Correlations have been proposed to predict gas hold up and axial dispersion.

Integration of unsteady friction models in pipe flow simulations

Various approaches to integrate instantaneous acceleration models are examined. The basic physical model consists of the one-phase flow water hammer equations with the unsteady wall friction model of Brunone. The numerical scheme is based on characteristic upwind finite differences, representing an extension of the Godunov schemes to the non-conservative hyperbolic equations. The most accurate solutions result from the basic version of this method, which takes into account the effects of spatial and temporal derivatives of the unsteady friction term on the eigenvalues of the hyperbolic equations. A convergence analysis shows that second-order accuracy is obtained on smooth solutions with this approach, but only if the discontinuity in the unsteady friction correlation is removed. Two simpler numerical schemes treat the unsteady friction term as a source term and neglect its influence on the eigenvalues. The results obtained with the simplified schemes converge to the exact solutions, but exhibit larger numerical diffusivity than the basic version of the method.

Study of Flow in a Blanket Clarifier Using Computational Fluid Dynamics

This work simulated the flow pattern of the sludge blanket clarifier at the Bansin Water Treatment Plant, Taiwan by multiphase flow, three-dimensional analysis. The following three models were developed individually: One-phase flow (water) in the clarifier—this model acquires the basic water-flow pattern; a homogeneous porous medium at the bottom of the clarifier—this porous medium represents the sludge blanket; and, the Eulerian granular multiphase model, which was utilized to obtain solid effluent flux and to determine the effects of particle size and density on sludge blanket stability. Analytical results indicated that the clarifier has two principal circulations inside and outside the reaction well. A plentiful, dense and thick sludge blanket should exist at the clarifier bottom; otherwise particles could flow out through the gap between bottom of the reaction well and top of blanket surface, resulting in poor water quality. In the multiphase flow model, large particles and a high particle density ar...

Developing Flow Correlations for Different Valve Geometries Using Reference Media for R-744

This paper presents experimental data of three different prototype valves with cone-, ball-, and slide-valve geometries that have been tested using R-744 and two reference media, ARAL 4005 and R-729, under one-phase flow conditions. Three different test rigs were used to carry out the tests using boundary conditions with the objective to achieve more or less similarity regarding the Reynolds number and the Mach number. One aim was to find physical-based flow correlations to describe the flow behavior of the three investigated valve geometries with carbon dioxide (R-744), hydrocarbon-based low-viscosity fluid (ARAL 4005), and air (R-729) as the fluid. The main goal of this research was to find a correlation between the flow coefficients of both (a) R-744 and ARAL 4005 and (b) R-744 and R-729 to enable the transfer of a flow coefficient measured for ARAL 4005 or R-729 into a flow coefficient for R-744.