Abstract
Original language  English 

Qualification  Master Degree 
Awarding Institution 

Award date  15 Jan 2015 
Place of Publication  Espoo 
Publisher  
Print ISBNs  9789513883157 
Electronic ISBNs  9789513883164 
Publication status  Published  2015 
MoE publication type  G2 Master's thesis, polytechnic Master's thesis 
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Keywords
 VOF
 CFD
 twophase flow
 hydrodynamics
 free surface
 FINFLO
 YAFFA
 numerical modelling
 convection
 interface capturing
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Verification of a homogeneous micture model for the free surface problem : Master's thesis. / Viitanen, Ville.
Espoo : VTT Technical Research Centre of Finland, 2015. 192 p.Research output: Thesis › Master's thesis
TY  THES
T1  Verification of a homogeneous micture model for the free surface problem
T2  Master's thesis
AU  Viitanen, Ville
PY  2015
Y1  2015
N2  In this thesis, the applicability of the homogeneous mixture model of FINFLO for the free surface problem is studied. The free surface problem is fundamental in marine hydrodynamics, and a special case in twophase flows. The work explores the basis of this type of modelling from mathematical and numerical viewpoints, and verifies the mixture model for the problem. The mathematical background of the problem is presented, together with the nature of it from the perspective of marine hydrodynamics. The bulk flow equations are usually averaged conditionally such that the governing equations of the multiphase model are formally the same as in the case of singlephase flow. It can be shown that one additional equation suffices for the description of the segregated phases. Here, the convection equation of the void fraction is utilized. The void fraction equation is derived in conservative form based on the incompressibility constraint of the individual phases. The convection of the void fraction corresponds to the socalled Riemann problem. This is studied thoroughly by developing a twodimensional solver for the comparison of some wellknown schemes for the spatial discretization of the convective quantity. This solver is applied to the convection of a discontinuous distribution of the void fraction. In addition, the socalled SUPERBEE limiter is implemented to the FINFLO code for the extrapolation of the convective void fraction. The numerical solution of the NavierStokes equations for simulations of twophase flows is covered comprehensively. The code YAFFA, developed at the Aalto University, has a modern VOF model implemented, and for this reason, it is here used as a reference code. The solution algorithms, the computation of the convective quantities, the pressure correction stages as well as the treatment of the segregated phases in both of the codes are discussed in detail. The twophase flow over a submerged ground elevation is computed using the codes FINFLO and YAFFA, and the forming free surface wave is compared to the corresponding results found from the literature. The aim of this thesis is to get acquainted with the nature of the problem in conjunction with the specific methodology used to solve such flows. This is done in order to understand the requirements and possible modifications needed for the model when we wish to accurately predict ship flow phenomena that are not solvable using the traditional free surface tracking strategies. This way, the verification of the mixture model of FINFLO is achieved.
AB  In this thesis, the applicability of the homogeneous mixture model of FINFLO for the free surface problem is studied. The free surface problem is fundamental in marine hydrodynamics, and a special case in twophase flows. The work explores the basis of this type of modelling from mathematical and numerical viewpoints, and verifies the mixture model for the problem. The mathematical background of the problem is presented, together with the nature of it from the perspective of marine hydrodynamics. The bulk flow equations are usually averaged conditionally such that the governing equations of the multiphase model are formally the same as in the case of singlephase flow. It can be shown that one additional equation suffices for the description of the segregated phases. Here, the convection equation of the void fraction is utilized. The void fraction equation is derived in conservative form based on the incompressibility constraint of the individual phases. The convection of the void fraction corresponds to the socalled Riemann problem. This is studied thoroughly by developing a twodimensional solver for the comparison of some wellknown schemes for the spatial discretization of the convective quantity. This solver is applied to the convection of a discontinuous distribution of the void fraction. In addition, the socalled SUPERBEE limiter is implemented to the FINFLO code for the extrapolation of the convective void fraction. The numerical solution of the NavierStokes equations for simulations of twophase flows is covered comprehensively. The code YAFFA, developed at the Aalto University, has a modern VOF model implemented, and for this reason, it is here used as a reference code. The solution algorithms, the computation of the convective quantities, the pressure correction stages as well as the treatment of the segregated phases in both of the codes are discussed in detail. The twophase flow over a submerged ground elevation is computed using the codes FINFLO and YAFFA, and the forming free surface wave is compared to the corresponding results found from the literature. The aim of this thesis is to get acquainted with the nature of the problem in conjunction with the specific methodology used to solve such flows. This is done in order to understand the requirements and possible modifications needed for the model when we wish to accurately predict ship flow phenomena that are not solvable using the traditional free surface tracking strategies. This way, the verification of the mixture model of FINFLO is achieved.
KW  VOF
KW  CFD
KW  twophase flow
KW  hydrodynamics
KW  free surface
KW  FINFLO
KW  YAFFA
KW  numerical modelling
KW  convection
KW  interface capturing
M3  Master's thesis
SN  9789513883157
T3  VTT Science
PB  VTT Technical Research Centre of Finland
CY  Espoo
ER 