The Proceedings Fifth International Conference on Numerical Ship Hydrodynamics (1990) / Chapter Skim
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Finite-Difference Simulation of a Viscous Flow about a Ship of Arbitrary Configuration
Finite-Difference Simulation of a Viscous Flow about a Ship of Arbitrary Configuration
Pages 119-132
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From page 119... ...
Kajitani University of Tokyo Tokyo, Japan Abstract The improved version of the WISDAM-II method, a finite-difference solution method for a three-dimensional viscous flow about a ship of arbitrary configuration, is described. A zonal method is used for the boundary-fitted coordinate system so that the boundary layer is sufficiently resolved with proper boundary conditions on the body surface.
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From page 120... ...
to the imaginary transformed region R (E ~ ,$ 2,$ 3 ) , where the streamwise direction is approximately parallel to the ~ ~ direction, the lateral grid lines are approximately perpendicular to the ship hull surface are in the ~ 2 direction, and the grid lines parallel to the girth line of ship hull is the ~ 3 direction.
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From page 121... ...
Some simulations have shown excellent agreement with the averaged experimental results. But nobody so far answered several fundamental questions how the flow of the boundary layer is deformed to develops into wake and how is the transition from laminar to turbulent flow on the surface of the forepart of a hulL In order to investigate into the fundamental physical features of the turbulent flow around a ship, the authors employ a zonal method near the ship hull surface, and on the other hand adopt a computational procedure with SGS turbulence model, the latter of which is similar to large eddy simulation and is called LES-like procedure by the authors.
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From page 122... ...
~=Yleyl[l-e-y+/A ] and the boundary layer thickness ~ and the dispalcement thickness ~ are obtained as ~ — 1 .93 6ymnX Also both the accelerated and the decelerated flows including separated flows are considered in this formulation of the modified CebeciSmith model, see Stock and Hasse [17]
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From page 123... ...
is not very satisfactory since the flow is not f ully developed and f urthermore in the algebraic turbulence model used in this study the displacement thickness of the boundary layer is determined by the well-known Coles velocity profiles for the zero-pressure gradient [17] while the decelerated flow near the after end of ship is involves large pressure gradient.
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From page 124... ...
The use of zonal method described here will be one 124 of the promising approach. For the numerical simulation of the detailed viscous flows on the hull surface we must be very careful as suggested by the present test computations The zero-equation model ignores some of the Reynolds stresses which may not be sufficiently small in the real flow.
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From page 125... ...
. 13.Shumann, U., "Subgrid scale model for finite difference simulations of turbulent flows in plane channels and annul)
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From page 126... ...
OVERLAPPING REGION O ll Fig.2.2 Definition sketch for the interfacing region Fig.2.3 Grid system for the zonal method (transverse section) , coarse (left)
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From page 127... ...
and the location of maximum Reynolds stress (Y max) , blank and black marks are for the SGS and the zero-equation model,respectively, and numbers in parentheses indicate location.
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From page 128... ...
1 O 15 0.2 0.25 0.3 Eddy viscosity Vt#105 O - , , , , t , , , , :, , I -400 -200 o 200 Reynolds Stresses Fig.7.3 Computed results with the zero-equation model at ~ 1=110, T=1.2.
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129 ] ___ 0 200 400 Reynolds Stresses
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From page 130... ...
I I I I I I ~ -500 0 500 Vorticity 0.1~- _ oW~ 1 , , , , 1 , , , ,~ Eddy Viscosity Vt* 103 2 0.1 ~ n I v ~ ~ ~ J 1 ~ ~ ~ -200 - 100 0 100 200 Reynolds Stresses F:g.7.5 Computed results with the SGS model at ~ ~=110, T=0.8.
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From page 131... ...
~ ~ - 200 - 1 00 0 1 00 Reynolds Stresses 500 1, 01 _ ~ o A, 1,, 1 1 1 1 1 1 1 1,, , o 05 1 1 5 Eddy Viscosity Vat l 0~ o o o o o 200 Fig. 7.6 same as Fig.
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