Twenty-Third Symposium on Naval Hydrodynamics (2001) / Chapter Skim
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Simulation of Incompressible Viscous Flow Around a Ducted Propeller Using a RANS Equation Solver
Simulation of Incompressible Viscous Flow Around a Ducted Propeller Using a RANS Equation Solver
Pages 527-539
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From page 527... ...
-l ow ar o Ed c mar me ducted propeller is simulated by solving th RANS equttiorr with the kid turbulence model The FPNFLO solver developed et Helsinki Umversity of Techmology is used in She calculation F NF O is c mult~block cellcentered fmitewol me computer code with sliding mesh mm tag g id Ed fre-surice cm~oilities in f is paper, the flow over c lie series propeller Ed NSMR nozzle 19A is analyzed Th concocted flow patterns doss tream of th propeller Ed duct are illustrated Ed compared with experiments for one advance n mber Calculated f ~ t Ed torque are also provided for several advance n mbers Good correction with experiments is obtained in terms of force coefficients Ed velocity distributions INTRODUCTION Ducted propulsors are k ow to offer sigmflc mt cdvmtages for particular marine applications Since 1931, they hive been fi st mstalled m t 3., pushbocts, tTtsslers, Ed Inter m research vessels, d illing platforms, submersibles, etc There are some mstalktions in commercial ships, Ike lard ttnl.erS Ed buk carriers, Ed warships like mmal destroyers Ed submarines Among She benefits of d t led propulsors are remarkable incenses m efficiency for high propeller loadi 3. with flow- ccelercti g ducts, or citerrurtively smaller propeller size; reduction of i flow velocity Ed, consequently, of cavitation Ed noise with flow-decelercting ducts; better cone ol over the i flow to the propeller; improvement of mcnenwxability Ed position-keepmg civilities of vessels; protection from damage to th propeller, etc From c Theoretical t mdpomt, the hyd odynamic inrertorion betw en duct Ed propeller produces c twofold effect O the one h Ed, the presence of the duct permits to h m fer the me m lif mg truce on the propeller blade closer to She propeller tip, which in tom efficiently deflects th truce to c direction near that of She ship's motion On She other h Ed, the radial cone action of She flow due to the propeller action results in m cdditiorurl f ~ tmg truce on She duct, which mcreses She total f lust of the propulsor mit provided chat She loading is sufhciently high to overcome the duct viscous d cg How ver, Here is m upper limit also for the duct loadi g, which is detemmined by the risk of flow separation, es w 11 es for the propeller loading, which is detemmined by the risk of cavitation et the propeller tip The design of c d t red propeller is, the~efme, c complicated process in which She desig er of en has to make c comprom ise benison co flictmg ~equi ements in such cases, having access to i formation on She details of the flos-.1ield m problematic areas is most valuable for c successf I desig Most of She nrLtlv is methods for d t red propulsors have t en based on potential th ory, using m actuator disk (Gibson Ed Lewis, 1973; Gibson, 1974; Ftlc.i3 de Ccmpos, 1983, etc 1, lifimg-line or Iffting-smfce approaches lierss: et cl 1987; H ghes & Kimus, 1991, etc)
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From page 528... ...
Rce tly,the mteldyflowltomdt ht torthruster wls simullted usmg t slidmg mesh techmique md t compttison of some tvailble expttime ttl dttt to computed re mlts wt s p~esented (Stm hez-Ctjt, et t I 1999) The sliding mesh techmique was fo md robust for the tmt Iy is of fhe time-depende t vit ous flow The comp tttions w ~e performed in t quasi-steady md time~cc ttte mtmnet The former ~educed fhe CPU time to tbout 1/10 rektive to fhe ktter its mt m merit consisted of demet smg fhe CPU time while mt mtt mmg t f 11 rep~esentation of fhe propellf t geomeby, ie without inhoducmg simplifled models for simulati g fhe propellf t t tion, such t s t tuator disk or body force models ~ the p~ese t study, the flow t to md t ducted propeller mit is considered Ew~n though fhe mit consists of t rotating pt tt (th propeller)
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From page 529... ...
NUhdEtBICAL BEtSULTS Gt~mttty, Mmh and Boundaty Conditiont The case selected for tmtly is is 6he ducted propeller pret nted m Kt wtkita (1992) The propeller hts five bkdes, t ditmeter of 0221 m tmd t pitch rttio of 0 9741 it belongs to th NSMR Kt series The duct is NSMR nozzle no 19A The clet ttm tt the propeller tip is 0 72% of 6he propeller ditmeter LDV met smements w ~e reported t t t rt te of rott tion of 25 rps conespondmg to tm t dvance coefhcient of
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From page 530... ...
Special emphasis was put on modeling the propeller blades and their near-wakes accurately. The only noticeable difference in geometry from the ducted propeller model was that the hub of the computational grid was extended downstream of the propeller, as is the practice of MARIN, whereas the experimental model has it extended upstream.
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From page 531... ...
n.o~t ~ -0.060 _ o .0.044 -o.o~o _ .o.o.. -o.o`e oosz 1 1 -0.0s2 _ 4000 8000 12000 0 CYCLES Figme 3 Cormergence histo y of fhe ove~all Ifft coeffcient Th hub 2md bkde surfaes of the propeller 2re rotating solid w211s wifh bo md2 y conditions e forcmg the velocity fleld to match fhe propeller rotatiomd speed The velocities 2t fhe duct surfae 2re set to :D:ro m order to sati fy fhe non-slip bo md2 Y condition Th 12te~a1 surfaes adjaent to fhe propeller bkdes 2md duct have cyclic or periodic bo md2 y conditiom Th block bo mdaries where two 2diaent block surfaes 2 e comcident 2 e deflned 2s com~ectivities A miform flow condition is aplied to fhe inlet 2md periph rical smfa s Th st~eamwise g 2dients of fhe flow variables 2re set to :D:ro 2t fhe outlet Convergence Th computations w re performed on a SGI Origin 2000 mahine Eight processors were used The computation time was 13 seconds per iteration cy le For the second g id level, fhe computation time was 1/8 times fnat of the flrst g id level A satisfatory cor~rgence was obtained with 2 Courat n mber of O 5 usmg two multig id levels Th corwergence histories of the ove~all lid 2md d 2g coefficients 2 e prese ted m Figs 3 2md 4 After 3000 iterations, fhe over211 d 2g coefficient cormerged withm 1% of fhe final value, 2md fhe over211 Ifft coefficient withm 0 5% Figure 5 shows 2 magmflcation of the convergence history for fhe cwv211 Ifft coefhcient Figme 4 Cormergence histc-coefficient -O 0.ss: ~°'°488 I 111~ ~ -0.04s7 4000 sOOO t2000 CYCLES ~ry of the over211 d 2g \~/~~ .o.o~ss~ ~ 0 dooo sooo t2000 CYCLES Figme 5 Cormergence history of the over211 lid coefficient Mag ffication Forces and Presares The k~ tmbulence model gave 2 good conelation of flow patterns 2md pe formance coefficients with measmements T2ble 11 shows that th perform2 e coefficients w ~e c21cu12ted for advance n mber 0 5 wifhin 4 5% of fhe measureme ts ~ p2 ticul2, the thrust coefhcient for fhe propeller ~TR)
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From page 532... ...
Distribution of pressure difference on the pressure side of ducted propeller NSMB l9A. Velocities and Hydrodynamic Pitch Figure 9 illustrates the circumferential variations of the velocity components downstream of the propeller plane at r/R=0.5, 0.9, 1.0 and 1.05, and at x/R=0.65 (just behind the duct)
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From page 533... ...
Calculated velocity contours downstream of the ducted propeller (J=0.50, x/R=0.654. Figures lOa and lOb provide a comparison of experimental and calculated velocity contours at the same axial location.
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From page 534... ...
vx above 2.1 1.9 1.7 1.5 1.3 1.1 0.9 0.7 Below, Figure 12b. Calculated velocity contours downstream of the ducted propeller (J=0.50, x/R=1.004.
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From page 535... ...
In this reference, the hydrodynamic pitch angle of the trailing vortex wake of the ducted propeller was calculated in the experiments using the averaged axial and tangential velocities VX and vt as flow = tan ~ ~ (7) rQ + vie It seems apparent that a small error was made when the above formula was applied: the circumferential mean tangential velocity was introduced in the formula with a positive sign instead of the correct negative one.
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From page 536... ...
"A m mericcl method for solvmg mcompressible vi pops flow problems," Jop pal of Computatiorul Phvsics,2:12-26,1967 Fcic lo de Ccmpos, JA C, "On th Ccicpktion of D cted Propeller Perfommance m A i-symmetric Flows," Techmiccl R port 696, Netherl mds Ship Model Bcsin, Wcgeni gen, l 983 Gibson, I S md L wis, Rl, "Dpcted Propeller Apalysis by Sp face Vorticity md Actpator Disk Theory," Procedings of the Symposipm on Dpeted Pr one llers , the Roycl Instit t ion of Naval A chitects , Teddington, E ghmd, Mcy 1973 Gibson, I S "Themeticcl Studies of Tip Clearance md Rsdicl Variction of Bkde Loadmg on th Operction of D cted F ms md Propellers," Jop pal of M ph miccl E ~meerm~ Sciep e, Vol.
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From page 537... ...
md P m, H -C , 1 992, "A Application of Roe's M thod for fhe Simpiction of Viscop Flow m Tp bomcchmery," Fi st Ep ope m Computatiopal Flpid Dvnamics Co ferep e, Brpssels, 7- 1 I Sep 1992 Siikop n, T
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From page 538... ...
Highfidelitydesignoptimi ction The time seems mat re to consider propulsor design optimization et RANS level High pe formcnce computing techniques for optimization using high fidelity physicsbased models have advanced th ough the rapid development of cdjomt formulation The cdjoint approach greatly reduces the mmmber of flow simulations for computing sensitivities of design variables in the optimization process md makes the design optimizati m feasible et the detailed design stage (2) Ease of use md implementation Seamless integration of date t msmission betw en file desigogeomeby mdthe surface represe tation for RANS simulation is highly desuable A adaptive md versatile grid ystem that cm offer users more flexibility m grid layout is definitely need d Unstructmed grid approach may seem to be the way of griddmg for the futme (3)
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From page 539... ...
42, No 2, 2000, pp 247-264 AU7 HORS REPLY We would I ke to f mk Dr Dci for his valuable comments on She present concerns Ed future trends of RANS applications to propulsor design Ed crurlysis We agree with his views Ed m my of the topics he has quoted are subject to contimmous research m our Institutions He hr. mentioned th e major areas that should be add essed when using RANS codes es part of the design work With respect to grid generation w would like to point out that care should be taken for the definition of She grid shape She designer should define the grid shape in such c way Nat legions with trong gradients of flow qu mtities are correctly ccptmed by core enn ctmg enough mmmber of cells in such areas She grid that w have used in the computations is stmct red in such c way There is c high concentration of cells in She propeller wake for x/R<0 7, which explains She good correction of flow patterns et x/R=0 65 On the other h Ed et x/R=1 0 the correction is not so good since the grid is not following the wake mymore et this location, Ed She size of She cells is relatively large A other topics that should be mentioned are the criteria of convergence Ed the boundary condition In this calculation w get relatively fast c d op by thee orders of mcgnit de m pressure residuals, but this does not guar mtee the convergence of oveeall qu entities like th ust Ed torque Boundary conditions Nat reproduce in c mat Al way the physics underlying the hyd odynamic problem are key to solving it m c fast mdaccu~ateway DISCUSSION K Nakatake Ky shu University, Up m I cm impressed by your huge CFD calculations In She region behind She propeller hub, Here is c white region of velocity field Could you cclcubte the propeller hub vortex by your CFD scheme?
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