Twenty-Third Symposium on Naval Hydrodynamics (2001) / Chapter Skim
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Optimizing Turbulence Generation for Controlling Pressure Recovery in Submarine Launchways
Optimizing Turbulence Generation for Controlling Pressure Recovery in Submarine Launchways
Pages 171-180
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From page 171... ...
A comparison of She predicted frictional coefficient with the zt-sez measur merits shows flat the Fictional coefhcient is independent over Rey olds mmmbers sparming It least th ee crders-of-magnitude INTRODUCTION NO y design engineers require trict conhol over the extent of pressure recoven d insid submarin recessed hull cavities Ed vehicle kunchways to Insure successful underset operations during reconnaissance Ed delense missi ms in cases where She differed e betw en the hyd odynamic performance of the submarin vehicle shutterway n cess with respect to the pump inlet cavity promotes z reverse flow th ough She com cting I muchway mech mism, m adverse pressure a. dient pa Exists across the vehicle just prior to I much This pressure differed e must be overcome by She pump itself dmmg tart~p Funh n ore, given sufficient pressure differ e, m initial breachward movement of the vehicle may occur that m result in unacceptable hunch damage The following work presents z flexible measure for conhollmg She level of pressun recovered in the submarin I muchway to avoid the adverse hunching conditions just described Specifically, f is measure in olves plac merit of periodic ribs in the submarin cylmd ical shutte way end of the vehicle kunchway that m suitable minimize She level of the pressure recovered (or maximize pressure loss)
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From page 172... ...
withm ~ cylind ical duct To asce tam the domi mt turbulent physics that me responsible for producing the static pressure loss Ed She resulting fiictiomal loss coefhcie t, ~ computation was conducted using the k Shoddy simulation LE3 1 methodology Since the energy-domim~te scales of the t rbulent field primarily attribute to th tatic poet me loss, LES is w 11-suited for this purpose The impet s of the LES methodology is f 11 resolution of the energybearmg scales of the turbulent motion while mod hng the smaller scales font tend towards homogeneous Ed isotropic conditions The salient turbulent featmes of She flow are presented in this paper Including its struct He Ed statistical quantities font on noble fiom She rib's presence Aldhough She prese t computations depict flow characteristics for ~ Rey olds mmmber se- eras orders of magnitude low r f m f 11-scale, She me m pressme loss is verified by at-sea met tuemem3 taken fiom ~ full scale prototype test onboard ~ US Na y submarine 0.1 _ 1 - (3~\ 3 ~` .~N : _ Webb (iill1 _ __ WaSSel ~ MrIlS (~979) 1 10 100 p/h Figme I Empu ical Relationships for Dere mini g the Fricti m Factor for Rib Roughened Ducts Table I Parameters Determined for the Relationships mFig 1; f =2[ltu(r/h)
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From page 173... ...
, fhe metric coefficients are considered es filtered bee mse fhey me evalllated mmmericMly et discrete pomts Mong the curvilit ar Imes(denotedbyatilde) he ctove LES sy tem was time~dvanced by c vari mt of the fractiot~l- tep method (Jordan md Rag~h, 1996)
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From page 174... ...
m idenri 91 form to that originally derived by Jordan md Rage (1995) Using the same eddy viscosity relationship, mod hag the modified Rey olds stress tensor becomes T} 1/3$ T,,=2CA2 s s, (6a)
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From page 175... ...
This figure clearly indicates that the streamwise vertical structures shown in the previous figure do indeed originate at the rib crests and require about two periodic lengths before fully convected radially to the primary duct core. These structures house the maximum and minimum magnitudes of circumferential vorticity in the entire duct flow.
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From page 176... ...
3 and 4. Lastly, the distribution of circumferential vorticity in both trough regions reveals little similarity and contributes modestly to the primary vertical flow.
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From page 177... ...
The periodicity of each quantity in the trough and core sections of the duct justifies imple meeting periodic boundary conditions in the streamwise direction as well as the total time required to reach statistical steady-state. Interestingly, the normal fluctuations reach their highest values along narrow bands within the core flow.
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From page 178... ...
CONCLUSIVE REMARKS The present work demonstrates control of the pressure recovered in a cylindrical duct through the pressure losses introduced by newly generated turbulent activity from periodic ribs mounted along the internal walls. Given a rib spacing to rib height ratio of s/h = 5 and respectively to the duct diameter (h/D = 0.1)
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From page 179... ...
Philips) st the Naval Underses Warfare C nter REFERENCES Berger, P
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From page 180... ...
AUTHOR'S REPLY First of all, let me thank Dr C lik md Dr Cordier for then comments md interest m the paper Both discussions question the use of periodic boundary conditions in the streamwise direction of the ribbed duct for representing c series of ribs that ingest new turbulent structures into the core flow The mew r to this question rests on justifying c correct set of flow conditions et these open boundaries bee mse Hey depend on the physics outside She flow domain This dependence is satisfied when setting These faces es periodic, but the turbulence is assumed to be statistically homogeneous or statistically periodic Sufficient separation of these boundaries is critical, where 'opnori' t ~ led e is Required of th two-pomt conelation length of the periodic streamwise stmct res in She case of subsequent ribs, the con canon length is simply She rib's pit h But for simpler geometries such es the turbulent charmel flow, the channel length mu t be et least twice the integral scale of the turbulence in the sheamwise direction The present LES computation tested the periodicity of the duct flow by simulating two ribs On She mst mtaneous level, periodic vorticcl stmctures w re computed within the core flow that on nailed along the lecdmg edge of previous rib Rest These stmctures w re convected Radially towards She duct center over two periodic lengths to reach Heir streamwise position The instmtmeous stmct res withm the trough regions, how ver, showed discernible differences Thus, the trough regions sufficiently guided the computation towards statistical stecdy-state given periodic boundary conditions along She inlet md outlet faces Previous date es w 11 es f 11-sccle measurements taken of the present design show that the flow's memory from nomperiodic inlet conditions occurs only over the first two ribs This length appears mdependent of She present rmge of Rey olds mmmbers md scales closme of the separated shear Dyers Nat me growing radially towards She duct centerline Thus, the present LES computation, which employs streamwise periodic boundary conditions, mimics the actual prototype design fiom the third rib md beyond Direct comparisons of the mean flow date taken from She full-sccle prototype md the present computation proved this point Given c target centerline pressure loss of c prototype design for the submarine I muchway, These LES results provide the requited design length plus two cdditiorurl ribs
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