Twenty-Third Symposium on Naval Hydrodynamics (2001) / Chapter Skim
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The Experimental and Numerical Study of Flow Structure and Water Noise Caused by Roughness of a Body
The Experimental and Numerical Study of Flow Structure and Water Noise Caused by Roughness of a Body
Pages 569-578
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From page 569... ...
As engine and other noises have been reduced in these days, the internal noise levels of many speeding submarines are significantly affected by the water noise. The main sources of water noise are as follows: Pressure fluctuations in the turbulent boundary layer; 2)
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From page 570... ...
at h a sonic Mah m mber But all 6he aove studies ae focused on te tmg ad dLag reducti m, 6hffe is little effcrts m 6heory ad I wffmg watff noise in 6his paff, how to low r the watff noise level by surfae r mg~mess is mve tigated he concept of madhematical roug mess is inhoduced, which deduced fr m 6he no-slip condition of vertex method he results sh w that mahematical roug~mess cmld kep in 6he vertex's sheddmg, ad it ca be c msidered as forward multi-lay r in dy amic phff omff a (Ga Lijm & 2h m Lia di 2000) But how to reah:D: 6he mahematical roug~mess m phy ics is a challenge he expffiment remlts show that certam r~blet or slot on 6he surfae has some relati m wi6h the mathematical roug mess ~ 6his papff, 6he i fluence of the roug mess is mvestigated An adative n mffical scheme, based on vort:x medhod, is used to solve a time-depff dff t f 11 Na ier-Stokes equati m he aaly es of flow fleld data ad s md field data mdicate 6hat 6hffe are s me shong relatims ammg 6he vertical motions ad tructures associated with the surfae roug~mess he chage of surfae roug~mess might be a new way to lOWff watff noise NUMERICAL METEIOD he flow was governed by m teady twodimffsimal mcompressible Na ier-Stokes equations, which ca be expressed m 6he vorticity trasfcrmation as: ~+u Va'=v a' .
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From page 571... ...
In this paper, the effect of the flow structure, vortex structure near the surface of the body and the water noise are observed when the roughness on the surface of the body was changed. After the enforcement of the no-through boundary condition, a tangential vortex sheet on the surface of the body could be observed, and the strength was yes)
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From page 572... ...
One model had normal surface, the other had rough surface on which some little cylinders of 23mm diameter and 1-2mm height were distributed orderly. The rough surface model could be shown in the Fig.
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From page 573... ...
The results indicated that the separation of the flow was strengthened and the seperated position moved ahead. It means that the positive mathematical roughness (backward multi-layer slip boundary condition)
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From page 574... ...
In Fig. 8, it shows that the vortex structure was decreased under mathematical roughness of or(s)
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From page 575... ...
~(s) = ~ 5 Fig 11: Watff noise mdff 150 attak mgle CONCLUSION The n merical md expffimental remits show 6hat 6he mhodueed mathffmatical roug~mess cm be cerresponded by 6he real phy ical roug~mess md could be used as usef I tool in irwestigati m of reduemg noise The positive mathematical roughmess m kes 6he water noise e haneed, md a negative mathffmatical roughness might redua: 6he watff noise (Gao Lidm & 2hm Limd6 2000)
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From page 576... ...
Comput tional Thy ics (1994a)
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From page 577... ...
Dr. Ulderico"Paolo" Bulgarelli Institute Nazionale per Studied Architettura Navale Via di Vallerano 139 00128 Rome Italy Tel: +39-6-50299-270/222 Fax: +39-6-5070619 E-mail: ~~os3.insean.~t Esperienze di Prof.
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From page 578... ...
>1 0 2 One-dbmensiomr1 LDV was used to measure She hori ontal velocity, which could not get the velocity m She boundary layer We only compared She velocity at She points where She experimental velocities w re achieved 3 E cmse of She time, we haven't made uncertainty analysis about our mmmerical method How ver we will do this work latter The negative mathematical roughmess is not rented to smoother surfaces th m normal rough su face The smoother rough su faces correspond to o < c |
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