Abstract
Original language  English 

Qualification  Doctor Degree 
Awarding Institution 

Award date  19 Sep 1997 
Place of Publication  Espoo 
Publisher  
Print ISBNs  9513850714 
Publication status  Published  1997 
MoE publication type  G5 Doctoral dissertation (article) 
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Keywords
 twophase flow
 flow velocity
 fluid flow
 SFAV
 subflow
Cite this
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Modelling of twophase flow based on separation of the flow according to velocity : Dissertation. / Narumo, Timo.
Espoo : VTT Technical Research Centre of Finland, 1997. 162 p.Research output: Thesis › Dissertation › Collection of Articles
TY  THES
T1  Modelling of twophase flow based on separation of the flow according to velocity
T2  Dissertation
AU  Narumo, Timo
PY  1997
Y1  1997
N2  This thesis concentrates on the development work of a physical onedimensional twofluid model that is based on Separation of the Flow According to Velocity (SFAV). The conventional way to model onedimensional twophase flow is to derive conservation equations for mass, momentum and energy over the regions occupied by the phases. This approach results in seemingly sensible equations but they need extra vague "virtualmass" terms to form a hyperbolic system or a mathematically wellposed initial value problem. Furthermore, the interface between the phases is unavoidably very complicated geometrically, which especially makes the modelling of interfacial momentum transfer between the phases highly problematic. In the SFAV approach, the twophase mixture is divided into two subflows, with as distinct average velocities as possible, and momentum conservation equations are derived over their domains. Mass and energy conservation are treated equally with the conventional model because they are distributed very accurately according to the phases, but momentum fluctuations follow better the flow velocity. Submodels for nonuniform transverse prole of velocity and density, slip between the phases within each subflow and turbulence between the subflows have been derived. The model system is hyperbolic in any sensible flow conditions over the whole range of void fraction. Thus, it can be solved with accurate numerical methods utilizing the characteristics. The characteristics agree well with the used experimental data on twophase flow wave phenomena. Furthermore, the characteristics of the SFAV model are as well in accordance with their physical counterparts as of the best virtualmass models that are typically optimized for special flow regimes like bubbly flow. The SFAV subflows enable easier interfacial momentum transfer modelling than in the conventional model because the interface between the subflows is geometrically much simpler than the interface between the phases. The SFAV model has proved to be applicable in describing twophase flow physically correctly because both the dynamics and steadystate behaviour of the model has been considered and found to agree well with experimental data. This makes the SFAV model especially suitable for the calculation of fast transients, taking place in versatile form e.g. in nuclear reactors.
AB  This thesis concentrates on the development work of a physical onedimensional twofluid model that is based on Separation of the Flow According to Velocity (SFAV). The conventional way to model onedimensional twophase flow is to derive conservation equations for mass, momentum and energy over the regions occupied by the phases. This approach results in seemingly sensible equations but they need extra vague "virtualmass" terms to form a hyperbolic system or a mathematically wellposed initial value problem. Furthermore, the interface between the phases is unavoidably very complicated geometrically, which especially makes the modelling of interfacial momentum transfer between the phases highly problematic. In the SFAV approach, the twophase mixture is divided into two subflows, with as distinct average velocities as possible, and momentum conservation equations are derived over their domains. Mass and energy conservation are treated equally with the conventional model because they are distributed very accurately according to the phases, but momentum fluctuations follow better the flow velocity. Submodels for nonuniform transverse prole of velocity and density, slip between the phases within each subflow and turbulence between the subflows have been derived. The model system is hyperbolic in any sensible flow conditions over the whole range of void fraction. Thus, it can be solved with accurate numerical methods utilizing the characteristics. The characteristics agree well with the used experimental data on twophase flow wave phenomena. Furthermore, the characteristics of the SFAV model are as well in accordance with their physical counterparts as of the best virtualmass models that are typically optimized for special flow regimes like bubbly flow. The SFAV subflows enable easier interfacial momentum transfer modelling than in the conventional model because the interface between the subflows is geometrically much simpler than the interface between the phases. The SFAV model has proved to be applicable in describing twophase flow physically correctly because both the dynamics and steadystate behaviour of the model has been considered and found to agree well with experimental data. This makes the SFAV model especially suitable for the calculation of fast transients, taking place in versatile form e.g. in nuclear reactors.
KW  twophase flow
KW  flow velocity
KW  fluid flow
KW  SFAV
KW  subflow
M3  Dissertation
SN  9513850714
T3  VTT publications
PB  VTT Technical Research Centre of Finland
CY  Espoo
ER 