Twenty-First Symposium on Naval Hydrodynamics (1997) / Chapter Skim
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Numerical Calculations of Ship Stern Flows at Full-Scale Reynolds Numbers
Numerical Calculations of Ship Stern Flows at Full-Scale Reynolds Numbers
Pages 377-391
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From page 377... ...
The grid dependency studies show that it is possible to obtain grid independent solutions in the flow around the HSVA tanker. The comparison of the solutions at model scale and full scale Reynolds numbers for the flows around the HSVA tanker and the Mystery tanker show a strong dependence of the flowfield on the Reynolds number.
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From page 378... ...
The reduced form of the RANS equations allows the use of large numbers of grid nodes even with modest computer resources, both in memory and c.p.u. The direct application of the no-slip condition at the wall and the use of the reduced form of the RANS equations make grid generation one of the major difficulties of full scale Reynolds number calculations.
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From page 379... ...
The inlet station, the outlet station, the free-surface, the symmetry plane of the ship, the ship surface and the external boundary. In the present calculations, the three velocity components at the inlet station were prescribed with standard boundary layer profiles, based on given momentum thickness and wall friction coefficient [123.
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From page 380... ...
A different grid sequencing technique is applied in the normal direction. Grid sequencing in the normal direction is mainly required by the clustering of grid lines close to the symmetry plane of the wake, imposed by the application of the no-slip condition at the ship surface.
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From page 381... ...
Furthermore, we do not apply grid sequencing in the global iteration sweeps performed with multiple stepsize factors 8 and 4. 3 Grid Generation If the RNS equations are chasers as the basis for a numerical simulation of ship stern flows the computational grid must be roughly flow confounding.
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From page 382... ...
The convergence criterion used in the global iteration process of all the calculations performed was a minimum pressure coefficient difference, (/\Cp~ma=, between consecutive sweeps of 5.0 x 10-3. In the local iteration process, CSIP, the convergence criteria was a maximum difference between physical components of the contravariant velocity components of 1.0 x 10-4Uoo and a maximum Cp difference between iterations of 2.0 x 10~ s .
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From page 383... ...
-0.20 < Cp < 0.35, /\Cp= 0.05 149 ~ n,~ _ -125 \ ~ - - - 105 ~ 49 125 -- - 105 \ Limiting streamlines Figure 2: HSVA tanker, Re = 2.0 x 109. Comparison of surface pressure distribution and limiting streamlines obtained with different numbers of grid nodes in the normal direction.
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From page 384... ...
Comparison of calculations performed with different numbers of grid nodes in the normal direction.
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From page 385... ...
These results suggests that it is possible to obtain a grid independent solution of the near-wall region in a ship stern flow at full scale Reynolds number. 4.3 Comparison of Solutions at E,ull Scale and Mode} Scale ReynoIcis Numbers The flow around the HSVA tanker and the Mystery tanker were calculated at full scale and model scale Reynolds numbers, 2.0 x 109 and 5.0 x 106, respectively.
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From page 386... ...
Comparison of calculations performed with different near-wall grid nodes density.
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From page 387... ...
x = 0.976 AU1 = 0.1 o.oo -o.oz N -0.04 0.06' ~ ' I 0.00 0.02 0.04 y / |
From page 388... ...
ACp= 0.05 ~~ i, Re5 ox~0.15 Figure 8: HSVA tanker. Comparison of surface pressure distribution for calculations performed at full scale and model scale Reynolds numbers.
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From page 389... ...
ACp = 0.05 Re ~ Figure 12: Mystery tanker. Comparison of surface pressure distribution for calculations performed at full scale and model scale Reynolds numbers.
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From page 390... ...
The comparison of full scale and model scale Reynolds numbers calculations for the HSVA tanker and the Mystery tanker confirmed a strong dependence of the flow field at the end of the stern on the Reynolds number. The limiting streamlines showed a systematic change in position of the confluence of limiting streamlines with increasing Reynolds number.
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From page 391... ...
-Recent Developments in a Ship Stern Flow Prediction Code. 5th International Conference on Numerical Ship Hydrodynamics, Hiroshima, September 1989.
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