Twenty-Fourth Symposium on Naval Hydrodynamics (2003) / Chapter Skim
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The Use of a RANS Code in the Design and Analysis of a Naval Combatant
The Use of a RANS Code in the Design and Analysis of a Naval Combatant
Pages 145-160
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From page 145... ...
demonstrating the overall maturing of the capability. Such computations provide an overall picture of the flow field in the immediate vicinity of the ship, which can aid in its understanding as well as a means to do trade off studies to evaluate design Viscous flow calculations using the Reynolds options.
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From page 146... ...
Potential flow solvers can provide this type of information quite well except where viscous effects may be important, such as in the immediate stern region of the boat. Consequently, most of the design effort for Gov't-2 involves the use of the potential dow solvers because of their overall efficiency compared to RANS codes.
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From page 147... ...
The bare hull calculations provide comparisons of the nominal wake and what impact the different bow dome shapes have on the flow into the propulsor. The final Gov't-2 geometry calculations are then compared with the experimentally measured data for the free surface along the hull, wave height behind the hull, and inflow to the propulsor.
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From page 148... ...
Bare Hull Configurations The grid generation strategy for the three bare hull grids, Concepts-2, -4, and -5, is the same in order to provide a fair evaluation of the different hull forms and not bias these conclusions because of differences in results due to grids rather than differences in geometries. No changes are needed to the inputs or boundary conditions of the flow solver.
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From page 149... ...
Concepts 2, 3, 4, and 5 are run with the double-hull or linear free surface boundary conditions. The transom topology used is a continuation of the hull surface grid collapsed to a singular pole at y=z=0.
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From page 150... ...
FLOW SOLUTIONS Three aspects of the flow solutions are discussed. The first involves the bare hull calculations, which provide information on the different bow dome geometries.
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From page 151... ...
Computed axial velocity contours for this configuration at several longitudinal locations are shown in Figure 8. a__ by_ Bare Hull Ccacopt 4_~ A:; Figure 8: Computed axial velocity contours for Concept4.
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From page 152... ...
With the Concept-5 bare hull calculations, both linear and nonlinear free surface solutions have been obtained with UNCLE v1.2.6. The presence of the free surface has little effect on the bow dome vortices or the viscous flow that would enter the propulsor.
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From page 153... ...
This is unlike many conventional surface ships where the propeller is operating in a nearly inviscid free stream flow field. Noticeable in this and the previous figure is the low velocity flow which has been pulled out from the boundary layer due to the vertical nature of the flow entering the propulsor.
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From page 154... ...
Concept 3 0 0.025 0.05 0.075 Z/L Figure 14: Axial velocity contours at 70% of the propulsor length.
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From page 155... ...
The strong turning to the outboard side of the propulsors helps give an indication of why the propulsors can have a strong effect on the free surface waves generated near them. The inboard turning of the flow, and its interaction with the skeg, provides a high axial velocity between the propulsors which was indicated in the axial velocity contour of Figure 14.
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From page 156... ...
Longitudinal wave cut data at various locations away from the hull is also available for comparison. At Y/B = 0.66, Figure 21, a comparison similar to that shown for the hull profile is obtained with the fine grid capturing the wave heights well, but the coarse grid has significant damping.
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From page 157... ...
This data was taken with a LDV system and axial velocity contours are shown with secondary flow vectors. The dominant feature is the vortex, which is generated at the bow dome, as was shown with the previous computations.
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From page 158... ...
However, the coarse grid is overly dissipative as seen from the overly thick boundary layer on the hull and the larger low velocity c) Fine grid area due to the vortex as compared to the finer grid solutions and measured data.
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From page 159... ...
Although the free surface is not included in the RANS calculations in the early design phase of this study, the RANS calculations do provide useful insight to aid in the design. Specifically, the RANS calculations provide information on inflow to the propulsor as well as a means to evaluate the different bow dome geometries identified.
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From page 160... ...
M., "Model and Full Scale Predictions of a Carrier Flow Field," NSWCCD-50-TR-2002/009, January 2002, Naval Surface Warfare Center, West Bethesda, MD. ITTC, "Report of the Resistance and Flow Committee," Proc.
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