Proceedings of the Sixth International Conference on Numerical Ship Hydrodynamics (1994) / Chapter Skim
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Session 9- Viscous Flow: Applications 2
Session 9- Viscous Flow: Applications 2
Pages 455-508
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From page 457... ...
It is shown that a suitable convex filet form can significantly improve the stability of junction horseshoe vortex and reduce the strength of vortex and the non-uniformity in the wake velocity profile. It is also demonstrated flee capability of the numerical approach in the design of vortex flow control devices.
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From page 458... ...
Three configurations including a baseline configuration consisting of a wing mounted on a flat-plate junction, a triangle fillet form, and a constant radius convex arc fillet form along the entire wing/flat-plate junction are presented here. The numerical solutions were used to evaluate the relative effectiveness of the three configurations.
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From page 459... ...
2.3 Transformation of the Equations The price that has to be paid for the simplicity of implementing boundary conditions using bodyfitted coordinate systems is the increase in complexity of the governing equations when the Cardesian coordinates is transformed to the nonorthogonal coordinate system. The vector operation in the transformed plane is V.V=~i'=~)
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From page 460... ...
inn J nn where ANN are the values of ~ at nearest neighboring points, ann are the standard matrix coefficients obtained using hybrid differencing normal to control volume faces, and sm is a mass source term, i.e. aU = maxi Du)
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From page 461... ...
involve the values of the normal velocity components on mass control volume faces, and these must be approximated somehow from the velocity components U'* at mass control volume centers.
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From page 462... ...
~. The Convex arc fillet form is a circular arc form of radius 0.1C along entire wing/flat-plate junction(See Fig.
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From page 463... ...
The velocity vector fileds in the synunet~y plane ahead leading edge of the wing are used to analysis the ability of each to improve the stability of the horseshoe vortex. It has been demonstrated that the numerical approach is a valuable tool for evaluation of the effectiveness of the fillet forms and the design of vortex flow control devices.
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From page 464... ...
1993 my: · - Mass control volume centers o = Mass control volume face centers Figure 1. Grid Structure and Numerical Molecule / 0~ CDS , 11 DS CDS = Central Difference Scheme.
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From page 465... ...
of ~ o If 1 DJ ~ O JO JO I\ \s ~ at]
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From page 466... ...
0 02 0.4 0£ not Y/C (c) Convex Arc Filleted Ca" Figure 6.
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From page 467... ...
Velocity Vectors Around Leading Edge of Wing at Z/C = 0.01 467
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From page 469... ...
This wake pattern is the result of evolution of the longitudinal vortex which is generated by the flow separation, in the thick turbulent boundary layer about the ship stern. Due to its complex nature, it is not surprising that this wake pattern can not be predicted well in the numerical calculations based on the ReynoldsAveraged Navier-Stokes equations (RANS)
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From page 470... ...
l.The three-dimensional flow separation from the hull surface; 2.The evolution of the induced longitudinal vortex and its interaction with the turbulent boundary layer; 3.The vortex structure near the propeller plane and the resultant distorted wake pattern inside the propeller disk; and 4.The difference of flow structure due to the change of stern hull configuration. The above four points may serve as the checking point to verify the degree of resolution and the appropriateness of the numerical method.
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From page 471... ...
becomes, For the incompressible viscous flow, the Navier-Stokes equation can be written into the rid= uiui+ 1 (Reid) following conservative form, , flu ~ dip T = F , (3)
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From page 472... ...
(22) Solution Procedure It is well known that the MAC-type algorithm is one of the best solution procedure for the time-dependent, incompressible viscous flow at a high Reynolds number.
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From page 473... ...
On the other hand, for full ship form such as the HSVA tanker, the use of the sub-grid scale turbulence model t17] t131 leads to a better prediction of the flow separation and the distorted wake pattern in the propeller disk than the other RANS simulations with the conventional models t11.
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From page 474... ...
The minimum grid spacing is set at 10-4. This grid spacing ensures the first grid point is set inside the sublayer in the ordinary turbulent boundary layer.
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From page 475... ...
Figs.10 and 11, for both the eddy viscosity and the velocity profile, indicate that the flow structures along this waterline are still those of a developing turbulent boundary layer at S.S.2. The agreements between the calculation and the theory for both eddy viscosity and velocity profile are fairly good.
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From page 476... ...
For the accurate prediction of wake pattern, it is quite important for the numerical simulation to reveal the flow separation as well as the evolution of separated vortex. This work showed the possibility and importance of turbulence modeling for thick boundary layer.
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From page 477... ...
t23] Research on the Design of Ship Stern Hull Configuration -- - Viscous Flow: Project SR 196, the Shipbuilding Research Association of Japan, 1985.
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From page 478... ...
minimum grid spacing 1.0 x 10~ . time increment 5.0 x 104 .
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From page 479... ...
4 x/L Fig. 5 Afterbody pressure distribution along the longitudinal axis HYbrid Turh~lence Model bY A {ur~ction ~ -~(Cp} ~ · Cp 1 0.8 _ ~0.6 0.4 _ n ~"""""% ~Sub-grid Scale Baldwin- Lomax Midship 0~6 0 7 0.8 0.
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From page 480... ...
OSw.L; 8AS~Ng ~>,\ Fig. 8 Grid system about SR 196A ship model (about bow and stern)
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From page 481... ...
boundary layer theory ..
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From page 482... ...
u 5 0 | ~-T~ ~ 45 40 35 u 50 45 40 35 30 25 20 15 ·1 0 5 ~n _ 25 20 1 5 1 0 o sor 45: 40: 35t u 30 25 ~ 20 _ 15 _ 1 0 _ ~ ._ - - ~~:. T~ waterline no.3 (SR196A)
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From page 483... ...
_°5' S.S. V/U,~U S R 1 9 6 ~ Eem~ment SRI 9 6C Eexpenma ~~ ~ Fit; | I | CalQllanon Fig.
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From page 484... ...
'as, S.s.
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From page 485... ...
~- 1 ,<~.8 ~ 4\ \~ \ Mu / U = .9 \/ Calculatior Fig. 12c Comparison of longitudinal velocity between the calculation and the experiment: propeller plane 48s
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From page 486... ...
Fig. 13 Three-dimensional iso-longitudinal vortex contour about the afterbody hull of SR196C Hernial Vortex Force : Ly = Ax u u i: By/ rev Helicity u Ls Voracity Vector Velocity Vector Semi Angle Fig.
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From page 487... ...
ISR196 B (V-shape) SR196 A (Original)
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From page 489... ...
The difference of the buttock flow due to shortening the length of the after body, the effect of waves on the viscous flow, the effect of the asymmetric hull geometry on the wake are studied. The oblique tow simulation is performed with this method by giving proper inflow boundary conditions.
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From page 490... ...
In this paper, the TUMMAC-IV code for ship waves is used for the design of the fore-body configuration of minimum wave resistance. Demihulls with both symmetric and asymmetric waterlines are served for numerical simulation and not only the optimal prismatic curve but also the optimal degree of asymmetry are derived by modifying the original code so that it may cope with catamarans.
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From page 491... ...
4. 3 Computation and results About 40,000 grid points were allocated in each part of the computational domain and the grid spacing is variable in the vertical direction, which is especially important for SSTH, because the wave height is very small in comparison with the ship length.
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From page 492... ...
The computation is started from the still condition and the flow is accelerated to the condition of 40kt by 2000 time steps with the time increment of 2 x 10 ~4, where time is made dimensionless with respect to the ship length and the steady advance speed of a ship. Almost steady viscous flow field is attained when the dimensionless time T exceeds 2.0.
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From page 493... ...
In the stage of flow acceleration to the steady advance speed, the lateral velocity component in the x2 direction is also accelerated in a way similar to that in the x ~ direction. The computational domain is stretched laterally so that a complete oblique tow condition is implemented.
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From page 494... ...
Watanabe et al., Numerical simulation of a viscous flow with free-surface wave about a ship by a finite-volume method, J
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From page 495... ...
Table 1 Principal p`articulcars of SSTH ferry design IHI Super Slender Twin Hull ~ SSTH ) ferry design Approximate dimensions and performance when fitted with propellers 90m craft 75.0m 19.4m 4.9m 2.3m 3600tonnes Lerlgth Up Breadth moulded Depth moulded Draught Gross tonnage Capacity -passengers -cars Maximum speed Main engines Propulsion system Range ;,:~..,~, -rim ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ _ ~ ~ ~ -_ .
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From page 496... ...
Fig. 4 Comparison of wave contour maps of bow waves of a tanker model, simulation ~ upper ~ and experiment ~ lower )
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From page 497... ...
Fig. 5 Comparison oftotal and waveresistance curves due to the difference of slenderness.
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From page 498... ...
> ~ ~t 1 ~/ OUTE~ I INHER 1 · I ; 1 ~1 ; 1 Fig. 6 Computational domain for the approximate treatment of a catamaran hull for TUMMAC-IV si mulations S i d e B o u ~ d n ~ y Bottom BoundarN Free Surface I ~ I ~ o.~)
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From page 499... ...
~ l ~ ~/~ Fig. 8 Comparison of simulated waste contours in the outer region of a catamaran at 40kt, contour interval is 0.01 nondimensional wave hei ght, M-P 1, M-P2, M-P3 and M-P4 from above, the contour interval is 0.05.
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From page 500... ...
Fig. 12 Simulated wave contours of the outer above ~ and inner ~ below ~ regions, the contour interval is 0.05.
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From page 501... ...
14 Pressure contours of M-P4 on hull surface and water plane, the contour interval is 2 x ~ 0~3, bow field ~ right land stern field ( left )
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From page 503... ...
, _ X =-0.46 = ~ to 1: / Fig. 18 Contours of longitudinal vorticity component of M-P4 with short stern, simulation with free-surface.
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From page 504... ...
lo;: Fig. 22 Comparison of longitudinal vorticity contours at the stern end of M-PI and the shortened model.
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From page 505... ...
1 1.4 1.6 1.8 2.0 2.2 Fig. 23 Time-historica1 variation of forces and moment in the simulation of the oblique tow case.
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From page 506... ...
Fig. 25 Pressure distribution on the hull surface o and waterplane of the 5 obliqu tow case, the contour interval is 2 x 10-3 ", ~4 )
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From page 507... ...
~1 2.0 3.D Thea ta Fig. 28 Yaw moment coefficient vs oblique tow angle.
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From page 508... ...
Author's Reply One of the shortcomings of such CFD simulation of waves in a restricted region is that the dispersive spread of wave system is not well realized. Therefore, the estimation of the relative magnitude of wave resistance must be made by either integration of wave energy in the computational domain or integration of the surface pressure distribution.
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