Numerical simulation of dispersed flows and evaluation of interfacial area and volume fraction

2006 ◽  
Vol 35 (10) ◽  
pp. 1169-1176
Author(s):  
Tadashi Watanabe
Keyword(s):  
Numerical Simulation ◽  
Volume Fraction ◽  
Interfacial Area ◽  
Dispersed Flows ◽  
Area And Volume

Modeling Recrystallization for 3D Multi-Pass Forming Processes

2007 ◽  
Vol 558-559 ◽  
pp. 1201-1206 ◽  
Author(s):  
Mihaela Teodorescu ◽  
Patrice Lasne ◽  
Roland E. Logé
Keyword(s):  
Numerical Simulation ◽  
Grain Size ◽  
Present Model ◽  
Static Recrystallization ◽  
Volume Fraction ◽  
The Other ◽  
Finite Element Code ◽  
3D Numerical Simulation ◽  
Fraction Distribution ◽  
Simulation Results

The present work concerns the simulation of metallurgical evolutions in 3D multi-pass forming processes. In this context, the analyzed problem is twofold. One point refers to the management of the microstructure evolution during each pass or each inter-pass period and the other point concerns the management of the multi-pass aspects (different grain categories, data structure). In this framework, a model is developed and deals with both aspects. The model considers the microstructure as a composite made of a given (discretized) number of phases which have their own specific properties. The grain size distribution and the recrystallized volume fraction distribution of the different phases evolve continuously during a pass or inter-pass period. With this approach it is possible to deal with the heterogeneity of the microstructure and its evolution in multi-pass conditions. Both dynamic and static recrystallization phenomena are taken into account, with typical Avrami-type equations. The present model is implemented in the Finite Element code FORGE2005®. 3D numerical simulation results for a multi-pass process are presented.

scholarly journals Flow topologies in bubble-induced turbulence: a direct numerical simulation analysis

2018 ◽  
Vol 857 ◽  
pp. 270-290 ◽  
Author(s):  
Josef Hasslberger ◽  
Markus Klein ◽  
Nilanjan Chakraborty
Keyword(s):  
Numerical Simulation ◽  
Direct Numerical Simulation ◽  
Turbulent Flows ◽  
Volume Fraction ◽  
Fluid Velocity ◽  
Small Scale ◽  
Flow Topology ◽  
Two Phase ◽  
Local Flow ◽  
Interface Curvature

This paper presents a detailed investigation of flow topologies in bubble-induced two-phase turbulence. Two freely moving and deforming air bubbles that have been suspended in liquid water under counterflow conditions have been considered for this analysis. The direct numerical simulation data considered here are based on the one-fluid formulation of the two-phase flow governing equations. To study the development of coherent structures, a local flow topology analysis is performed. Using the invariants of the velocity gradient tensor, all possible small-scale flow structures can be categorized into two nodal and two focal topologies for incompressible turbulent flows. The volume fraction of focal topologies in the gaseous phase is consistently higher than in the surrounding liquid phase. This observation has been argued to be linked to a strong vorticity production at the regions of simultaneous high fluid velocity and high interface curvature. Depending on the regime (steady/laminar or unsteady/turbulent), additional effects related to the density and viscosity jump at the interface influence the behaviour. The analysis also points to a specific term of the vorticity transport equation as being responsible for the induction of vortical motion at the interface. Besides the known mechanisms, this term, related to surface tension and gradients of interface curvature, represents another potential source of turbulence production that lends itself to further investigation.

scholarly journals ASHEE-1.0: a compressible, equilibrium–Eulerian model for volcanic ash plumes

2016 ◽  
Vol 9 (2) ◽  
pp. 697-730 ◽  
Author(s):  
M. Cerminara ◽  
T. Esposti Ongaro ◽  
L. C. Berselli
Keyword(s):  
Numerical Simulation ◽  
Large Scale ◽  
Volume Fraction ◽  
Radial Profile ◽  
Air Entrainment ◽  
Compressible Turbulence ◽  
Eulerian Model ◽  
Volcanic Plumes ◽  
Large Eddy ◽  
Non Equilibrium

Abstract. A new fluid-dynamic model is developed to numerically simulate the non-equilibrium dynamics of polydisperse gas–particle mixtures forming volcanic plumes. Starting from the three-dimensional N-phase Eulerian transport equations for a mixture of gases and solid dispersed particles, we adopt an asymptotic expansion strategy to derive a compressible version of the first-order non-equilibrium model, valid for low-concentration regimes (particle volume fraction less than 10−3) and particle Stokes number (St – i.e., the ratio between relaxation time and flow characteristic time) not exceeding about 0.2. The new model, which is called ASHEE (ASH Equilibrium Eulerian), is significantly faster than the N-phase Eulerian model while retaining the capability to describe gas–particle non-equilibrium effects. Direct Numerical Simulation accurately reproduces the dynamics of isotropic, compressible turbulence in subsonic regimes. For gas–particle mixtures, it describes the main features of density fluctuations and the preferential concentration and clustering of particles by turbulence, thus verifying the model reliability and suitability for the numerical simulation of high-Reynolds number and high-temperature regimes in the presence of a dispersed phase. On the other hand, Large-Eddy Numerical Simulations of forced plumes are able to reproduce the averaged and instantaneous flow properties. In particular, the self-similar Gaussian radial profile and the development of large-scale coherent structures are reproduced, including the rate of turbulent mixing and entrainment of atmospheric air. Application to the Large-Eddy Simulation of the injection of the eruptive mixture in a stratified atmosphere describes some of the important features of turbulent volcanic plumes, including air entrainment, buoyancy reversal and maximum plume height. For very fine particles (St → 0, when non-equilibrium effects are negligible) the model reduces to the so-called dusty-gas model. However, coarse particles partially decouple from the gas phase within eddies (thus modifying the turbulent structure) and preferentially concentrate at the eddy periphery, eventually being lost from the plume margins due to the concurrent effect of gravity. By these mechanisms, gas–particle non-equilibrium processes are able to influence the large-scale behavior of volcanic plumes.

scholarly journals The investigation of the cavitation processes in the radial labyrinth pump

2018 ◽  
Vol 8 (1) ◽  
pp. 322-328
Author(s):  
Moloshnyi Oleksandr ◽  
Szulc Przemyslaw
Keyword(s):  
Numerical Simulation ◽  
Cross Section ◽  
Volume Fraction ◽  
Mechanical Energy ◽  
Circular Cross Section ◽  
Back Side ◽  
Numerical Investigations ◽  
Numerical Research ◽  
The Moment ◽  
Velocity Pressure

Abstract The paper concerns the analysis of the cavitation processes in the flow passages of the radial labyrinth pump. The object of the analysis contains the active (moving) and the passive (stationary) discs with straight channels trajectory and semi-circular cross-section. The conversion of the mechanical energy into hydraulic based on the exchange of the momentum between the liquid remaining in the moving and the stationary areas of the discs as well as on the centrifugal increase of the moment of momentum. The analysis of the cavitation processes was realized by the experimental research and the numerical simulation. In the article, the comparison of the cavitation characteristics was carried out. The numerical simulation had given similar results to the experimental one, the process of the cavitation was visualized. Furthermore, numerical investigations helped to describe the cavitation development. The results of the numerical research such as the distributions of the velocity, pressure and vapor volume fraction in the passages were presented. At first, cavitation starts on the back side and on the top of the wall between channels of the active disc. Further, the cavitation areas are growing along the axis of the channels. Eventually, they separation was observed and vortices of the vapour-gas mixture in the middle of the channels were formed. This phenomenon is so-called super cavitation vortices.

Numerical Simulation and Experimental Verification of Microstructure Evolution during the Seamless Tube Extrusion of Semi-Continuous Casting AZ31 Magnesium Alloy

2017 ◽  
Vol 898 ◽  
pp. 79-85
Author(s):  
Tao Lin ◽  
Ji Xue Zhou ◽  
Bai Chang Ma ◽  
Yun Teng Liu ◽  
Di Zhang ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Magnesium Alloy ◽  
Continuous Casting ◽  
Dynamic Recrystallization ◽  
Volume Fraction ◽  
Seamless Tube ◽  
Compression Tests ◽  
Extrusion Speed ◽  
Tube Extrusion ◽  
Az31 Mg Alloy

Based on the stress-strain curves at the temperature of 300-450 °C with strain rate of 0.01-1 s−1 by hot compression tests, the empirical dynamic recrystallization models for the semi-continuous AZ31magnesium alloy were developed. The dynamic recrystallization evolution during the seamless tube extrusion of the AZ31 Mg alloy was simulated by numerical method with the derived models and validated by experiment measurements. The results show that at certain extrusion speed the influence of the extruding temperature on the dynamic recrystallization fraction was significant. With the increase of the extruding temperature the volume fraction of dynamic recrystallization increase obviously. The predicted dynamic recrystallization fraction was in an excellent agreement with the experimental results.

The Influence of Major Diameter Solid Particle on the Double-Channel Pump Performance

2011 ◽  
Author(s):  
Yi Li ◽  
Qiaoling Cui ◽  
Zuchao Zhu ◽  
Zhaohui He ◽  
Baoling Cui
Keyword(s):  
Numerical Simulation ◽  
Flow Rate ◽  
Sliding Wear ◽  
Volume Fraction ◽  
Particle Volume Fraction ◽  
Particle Diameter ◽  
Wall Region ◽  
Impeller Outlet ◽  
Anticlockwise Direction ◽  
Double Channel

Based on mixture model, the numerical simulation of solid-liquid two-phase flow in a double channel pump (Specific speed ns = 81) was carried out. The effects of particle diameter, particle volume fraction and flow rate on solid volume concentration distribution, relative velocity distribution and abrasion characteristics were studied. The results reveal that in the impeller, more particles concentrate at the nut of the shaft end and the edge of the impeller outlet. So those regions are worn seriously. The abrasive types are sliding wear on the impeller outlet edge and impact wear on the nut respectively. In the wall of the volute, the concentrated areas of particles move round the anticlockwise direction when the mixture flow rate is larger. The reason is the mixture velocity is larger as the flow rate increases, and meanwhile the centrifugal force and gravity force are invariable. So the particles move round the impeller rotational direction consequently. In the volute, particles concentrate on the tongue and wall region, especially on the sections I, II, V and VII. So the areas are easily worn out. The abrasive type is the heavy sliding wear in the volute wall. Numerical simulation results are consistent with the actual situation. It follows that the calculating method is feasible.

Numerical Study on Flow and Heat and Mass Transfer in Pulsating Heat Pipe

2019 ◽  
Author(s):  
Jian-Hong Liu ◽  
Fu-Min Shang ◽  
Nikolay Efimov
Keyword(s):  
Numerical Simulation ◽  
Mass Transfer ◽  
Heat Pipe ◽  
Gas Phase ◽  
Heat And Mass Transfer ◽  
Mixture Model ◽  
Volume Fraction ◽  
Pulsating Heat Pipe ◽  
Two Phase ◽  
Pipe Model

Abstract Numerical simulation was performed to establishing a two-dimensional pulsating heat pipe model, to investigate the flow and heat transfer characteristics in the pulsating heat pipe by using the Mixture and Euler models, which were unsteady models of vapor-liquid two-phase, based on the control-volume numerical procedure utilizing the semi-implicit method. Through comparing and analyzing the volume fraction and velocity magnitude of gas phase to decide which model was more suitable for numerical simulation of the pulsating heat pipe in heat and mass transfer research. It was showed there had gas phase forming in stable circulation flow in the heating section, the adiabatic section using the Mixture and Euler models respectively, and they were all in a fluctuating state at 10s, besides, the pulsating heat pipe had been starting up at 1s and stabilizing at 5s, it was all found that small bubbles in the heat pipe coalescing into large bubbles and gradually forming into liquid plugs and gas columns from the contours of volume fraction of the gas phase; through comparing the contours of gas phase velocity, it could be seen that there had further stably oscillating flow and relatively stabler gas-liquid two-phase running speed in the pulsating heat pipe used the Mixture model, the result was consistent with the conclusion of the paper[11] extremely, from this it could conclude that the Mixture model could be better simulate the vaporization-condensation process in the pulsating heat pipe, which could provide an effective theoretical support for further understanding and studying the phase change heat and mass transfer mechanism of the pulsating heat pipe.

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