A high-precision unstructured adaptive mesh technique for gas-liquid two-phase flows

2010 ◽  
Vol 67 (11) ◽  
pp. 1571-1589 ◽  
Author(s):  
Kei Ito ◽  
Tomoaki Kunugi ◽  
Hiroyuki Ohshima
Keyword(s):  
High Precision ◽  
Adaptive Mesh ◽  
Two Phase Flows ◽  
Two Phase ◽  
Mesh Technique

Unstructured Adaptive Mesh Technique for Gas-Liquid Two-Phase Flows

2010 ◽  
Author(s):  
Kei Ito ◽  
Tomoaki Kunugi ◽  
Hiroyuki Ohshima
Keyword(s):  
High Precision ◽  
Two Phase Flow ◽  
Adaptive Mesh ◽  
Dam Break ◽  
Phase Flow ◽  
Two Phase Flows ◽  
Two Phase ◽  
Distorted Mesh ◽  
Simulation Results ◽  
Mesh Technique

In the design study of large-sized sodium-cooled fast reactors in Japan (JSFR), the suppression of gas entrainment (GE) phenomena at a free surface in the reactor vessel is very important to establish an economically superior design. However, the GE phenomena are highly non-linear and too difficult to be evaluated theoretically. Therefore, we are developing high-precision CFD method for gas-liquid two-phase flows to evaluate the GE phenomena accurately. To reproduce the GE phenomena by CFDs, there are three key issues, i.e. geometry dependency, interfacial dynamics and locality. Former two issues are already addressed by employing unstructured mesh schemes and a high-precision simulation method for gas-liquid two-phase flow based on the PLIC (Piecewise Linear Interface Calculation) method, respectively. In fact, the simulation results of the GE phenomena in a simple GE experiment showed good agreements with experimental data. Recently, therefore, we focus on the locality of the GE phenomena. In our previous study (presented in ICONE17), the two-dimensional unstructured adaptive mesh technique for single-phase flows was developed to address the third issue. The isotropic cell refinement method was employed and the connection cell method was proposed to eliminate the edge incompatibility. The verification/validation results showed that the developed unstructured adaptive mesh technique succeeded in providing a high-precision solution, even though a poor-quality distorted mesh at the initial state was employed. In this study, the unstructured adaptive mesh technique is extended to the numerical simulations of gas-liquid two-phase flows. The redistribution methods of two-phase flow variables are newly developed to satisfy the conservations of the variables, i.e. the volumes of gas and liquid phases, the location of interfaces and the momentum of each phase. This improved unstructured adaptive mesh technique for gas-liquid two-phase flows is validated by solving the well-known slotted disk revolution and dam-break problems. As a result, the unstructured adaptive mesh technique succeeds in maintaining the slotted-disk shape after one revolution and shows more than first order accuracy (grid convergence) in the slotted-disk revolution problem. In addition, thanks to the momentum-conservative formulation, the dam-break phenomenon is well simulated by the unstructured adaptive mesh technique. Especially, wave-breaking phenomena are simulated by refined cells near the gasliquid interface. It should be noted that these simulation results are obtained by using relatively small number of cells because of the efficient mesh adaptation by the unstructured adaptive mesh technique.

Development and Verification of Unstructured Adaptive Mesh Technique With Edge Compatibility

2009 ◽  
Author(s):  
Kei Ito ◽  
Tomoaki Kunugi ◽  
Hiroyuki Ohshima
Keyword(s):  
High Precision ◽  
Flow Simulation ◽  
Adaptive Mesh ◽  
Two Dimensional ◽  
Initial State ◽  
Two Phase ◽  
Fine Mesh ◽  
Distorted Mesh ◽  
Cfd Method ◽  
Mesh Technique

In a design study of the large-sized sodium-cooled fast reactors in Japan (JSFR), one key issue to establish an economically superior design is suppression of a gas entrainment (GE) phenomenon at a free surface in the reactor vessel. However, the GE phenomenon is highly non-linear and too difficult to be evaluated theoretically. Therefore, we are developing a high-precision CFD method to evaluate the GE phenomenon accurately. The CFD method is formulated on an unstructured mesh to establish an accurate modeling for a complicated shape of the JSFR system. As a two-phase flow simulation method, a high-precision volume-of-fluid algorithm is employed in the CFD method. In addition, physically appropriate formulations at gas-liquid interfaces are introduced into the CFD method. The developed CFD method is already applied to the simulation of a GE phenomenon in a basic GE experiment and the simulation results show good agreement with experimental results. Therefore, it is confirmed that the proposed CFD method can reproduce a GE phenomenon. However, for the simulation of the GE phenomenon in the JSFR, we still have one problem on a mesh subdivision. Though a fine mesh subdivision has to be applied to the regions where the GE occurs, it is difficult to preliminarily know the regions because the GE occurrence is strongly affected by a local instant flow pattern, i.e. a vortex generation. Therefore, an adaptive mesh technique is necessary to apply a fine mesh subdivision automatically to only the local GE occurrence regions in the large-sized JSFR. In this study, as one part of an adaptive mesh development, a two-dimensional unstructured adaptive mesh technique is developed and verified. In the proposed two-dimensional adaptive mesh technique, each cell is isotropically subdivided to reduce distortions of the mesh. In addition, a connection cell is formed to eliminate the edge incompatibility between a refined and a non-refined cells. A connection cell has several subdivision patterns and one of them is selected to be compatible with adjacent cells on every cell edge. Finally, the present unstructured adaptive mesh technique is verified by solving well-known driven cavity problem. As the result, the present unstructured adaptive mesh technique succeeds in providing a high-precision solution, although we employ a poor-quality distorted mesh at the initial state. In addition, the simulation error on the unstructured adaptive mesh at the steady state is much less than the error on the structured mesh consisting of a larger number of cells.

scholarly journals Numerical Investigation of Two-Phase Flows in Corrugated Channel with Single and Multiples Drops

Fluids ◽  
2020 ◽  
Vol 6 (1) ◽  
pp. 13
Author(s):  
Gustavo R. Anjos
Keyword(s):  
Numerical Investigation ◽  
State Of The Art ◽  
Moving Mesh ◽  
Moving Frame ◽  
Arbitrary Lagrangian Eulerian ◽  
Two Phase Flows ◽  
Two Phase ◽  
Interface Deformation ◽  
Corrugated Channel ◽  
Mesh Technique

This work aims at investigating numerically the effects of channel corrugation in two-phase flows with single and multiples drops subject to buoyancy-driven motion. A state-of-the-art model is employed to accurately compute the dynamics of the drop’s interface deformation using a modern moving frame/moving mesh technique within the arbitrary Lagrangian–Eulerian framework, which allows one to simulate very large domains. The results reveal a complex and interesting dynamics when more than one drop is present in the system, leading eventually in coalescence due to the amplitude of the corrugated sinusoidal channel and distance between drops.

High-precision Coriolis mass flowmeter for bulk material two-phase flows

1994 ◽  
Vol 5 (4) ◽  
pp. 295-302 ◽  
Author(s):  
G. Dimaczek ◽  
H.-G. Fassbinder ◽  
A. Emmel ◽  
R. Kupfer
Keyword(s):  
High Precision ◽  
Bulk Material ◽  
Two Phase Flows ◽  
Two Phase ◽  
Mass Flowmeter ◽  
Coriolis Mass Flowmeter

ALE-FEM for Two-Phase Flows With Heat and Mass Transfer in Microchannels

2015 ◽  
Author(s):  
Gustavo R. Anjos ◽  
Norberto Mangiavacchi ◽  
Jose Pontes ◽  
John Thome
Keyword(s):  
Phase Interface ◽  
Computational Cost ◽  
Adaptive Mesh ◽  
Phase Method ◽  
Lagrangian Description ◽  
Arbitrary Lagrangian Eulerian ◽  
Two Phase Flows ◽  
Two Phase ◽  
Interface Position ◽  
Multiple Bubbles

A numerical method is described to study two-phase flows for single and multiple bubbles with phase change. The fluid flow equations are based on the Arbitrary Lagrangian-Eulerian formulation (ALE) and the Finite Element Method (FEM), creating a new two-phase method with an improved model for the liquid-gas interface in microchannels. A successful adaptive mesh update procedure is also described for effective management of the mesh at the two-phase interface to remove, add and repair surface elements, since the computational mesh nodes move according to the flow. The Lagrangian description explicitly defines the two-phase interface position by a set of interconnected nodes which ensures a sharp representation of the boundary, including the role of the surface tension. The methodology proposed for computing the curvature leads to accurate results with moderate programming effort and computational cost and it can also be applied to different configurations with an explicit description of the interface. Such a methodology can be employed to study accurately many problems such as oil extraction and refinement in the petroleum area, design of refrigeration systems, modelling of biological systems and efficient cooling of electronics for computational purposes, being the latter the aim of this research. The obtained numerical results will be described, therefore proving the capability of the proposed new methodology.

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