Twenty-Third Symposium on Naval Hydrodynamics (2001) / Chapter Skim
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Submarine Maneuverability Assessment Using Computational Fluid Dynamic Tools
Submarine Maneuverability Assessment Using Computational Fluid Dynamic Tools
Pages 820-832
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From page 820... ...
Purtha mora, using this tool tha grid topology is idanhcal f om ona casa to another so that tha numarical rasults ara mora raliabB, at Bast for comparison pu posas. This study has bean perfo mad on an axisting submarina for which modal tast rasults wera availabB, and calc~lahons hava baen dona on tha basis of usual captiva modal tast: r~ddar affactivanass tasts, obliqua towing tasts, and rotating arm tast in both vertical md horizontal pimas.
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From page 821... ...
The intermediate one, 800.000 cells, and the finest one, 1.400.000 cells. These numbers correspond to the case where the symmetry related to the vertical plane cannot be used (typically the cases of maneuvering in the horizontal plane)
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From page 822... ...
Rotation (vertical and horizontal planes! Fig 4: finest mesh Fig 5: "forward dive planes" mesh Pure incidence/pure drift Calculation cases have been chosen to coincide with the results of captive model tests available.
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From page 823... ...
Tests with the finest mesh still have to be performed. Since it is not possible to use any symmetry in the horizontal plane (which was not the case for vertical plane motions)
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From page 824... ...
0,2 Incidence (degrees) 4 ~ ~ 12 Coarse meshing; q=0,16 "forward planes" meshing; q=0,16 <~ Coarse meshing; q=0,20 Am "forward planes" meshing; q=0,20 Fig 8: Heave force for rotation in vertical plane (low rotation rates)
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From page 825... ...
COMPARISON WITH MODEL TESTS DATA Pure incidence (without rotations The slope of the curves resulting of calculation, representing the lift coefficient present a satisfying concordance with those of model tests in vertical plane. It is clear that due to the presence of the sail and the deck a submarine is not symmetrical in the vertical plane and therefore a non zero value is expected for heave force and pitching moment at zero incidence angle.
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From page 826... ...
a slight under estimation of heave forces by calculation. The results obtained in the horizontal plane are Amp 03calculation -02 -01 ~ ~ '.' 00 not as good as they were in the vertical plane.
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From page 827... ...
The pressure distribution on both sides of the starboard stern plane for the original mesh is presented on the following figure corresponding to 25 degrees deflection ofthe plane (by. On this picture, it can be seen that the pressure distribution over the flap (responsible for the lifting effect)
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From page 828... ...
In the horizontal plane, the lack of accuracy of yaw rate influence on the sway forces lead to a bad estimation of the stability indices. In this particular case, the submarine is predicted as being course stable though sea trials (and model tests)
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From page 829... ...
For this complex maneuver, the dynamic of the submarine is qualitatively well predicted as shown on figure 24 where the rates of turn simulated are compared to measurements. By_ ~~ roll rate - sea trials Troll rate - simulation pitch rate - sea trials pitch rate - simulation c' yaw rate - sea trials —yaw rate - simulation Fig 24: Rates of turn It is clear that for time domain simulation, the small errors encountered during the prediction of forces and consequently on components of acceleration is magnified by the integration.
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From page 830... ...
At this stage, the math matinal models used for the pu pose of m meuvering simulations arc the same as those developed for captive model tests analysis.
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From page 831... ...
AUTHOR'S REPLY The quasi steady approach we used to investigate the capacity of RANS code for submarine m moeuvrability studies hr. two cdv Stages: Using CFD cclcubtions es c mom ert al towing tmkgavetheopport nitytouse mexistingset of tools to quickly derive time domain simulations of m uloeu.~ et fi om cclcubtion of forces Results of calculation were du ectly c mparable to existing model tests data Ed could therefore lead, to c certain extend, to validation Although unstecdy ph nom ffk~ ar he during m moeuvres, the quasi steady cpproachhcs demon trcted for c long time its capacity to provide pertinent simulations of He behaviour of submarines ion conventional m Hoed n et For most cases, the dynamic of the submarine is relatively slow compared to the dynamic of unstecdy phenomena concerned Ed the see trials don't really show some major i fluency of unsteadiness A other problem of unsteadiness, which is not solved, is that the solution of steady flow cclculationc moot fheoreticcllybe consideredas the me m force acting on He body on which separation c mses un te tdiness in She flow (es it would be me tech d in c towing t mk or m c rotating arm facility)
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From page 832... ...
for c cycloidal f uster AD) or for c c on- em Oral propeller on c inclined shaft (3 D)
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