Abstract – This paper presents a method of rapid manufacture

used in the development of a regenerative pump impeller.

Rapid manufacturing technology was used to create complex

impeller blade proiles for testing as part of a regenerative pump optimisation process. Regenerative pumps are the subject of

increased interest in industry. Ten modiied impeller blade proiles, relative to the standard radial coniguration, were evaluated with the use of computational luid dynamics and experimental testing. Prototype impellers were needed for experimental validation of

the CFD results. The manufacture of the complex blade proiles using conventional milling techniques is a considerable challenge

for skilled machinists. The complexity of the modiied blade proiles would normally necessitate the use of expensive CNC machining

with 5 axis capability. With an impeller less than 75 mm in diameter

and a maximum blade thickness of 1.3mm, a rapid manufacturing technique enabled production of complex blade proiles that were dimensionally accurate and structurally robust enough for testing.

As more advanced rapid prototyping machines become available

in the study in the future, e.g. 3D photopolymer jetting machine, the quality of the parts particularly in terms of surface inish will improve and the amount of post processing operations will reduce.

This technique offers the possibility to produce components of

increased complexity whilst ensuring quality, strength, performance and speed of manufacture. The ability to manufacture complex

blade proiles that are robust enough for testing, in a rapid and cost effective manner is proving essential in the overall design

optimisation process for the pump.

Keywords: rapid manufacturing, rapid prototyping, rapid tooling,

NOMENCLATURE

A Crosssectionalarea (m²)

ABS Acrylonitrile-Butadiene-Styrene

CO2 CarbonDioxide

CFD ComputationalFluidDynamics

CNC ComputerNumericallyControlled

D Impellerdiameter (m)

FDM FusedDepositionModelling

HPC HighPerformanceComputer

MTON MetricTon

P Power (kW)

Q VolumeFlowrate (m³/s)

RM RapidManufacturing

RP RapidPrototyphing

RT RapidTooling

TWh TerawattHour

η Eficiency

φ Flowcoeficient

ω Rotationalspeed (Rev/min)

INTRODUCTION

Pumpsarethesinglelargestuserofelectricityinindustryin

theEuropeanUnionandenergysavingsof3%wouldresultina

1.1TWHp.a.reductioninconsumptionorasavingof0.54Mton

of2CO production [1].As industry attempts to make energy

savingsandreduceenvironmental impact, thispaperconsiders

the manufacture of impellers to compare the computational

predictionswithexperimentalresultsofaregenerativepumpwith

aviewtoimprovingpumpperformance.Thecomplexlow-ieldwithinaregenerativepumprepresentsasigniicantchallengetodetailed mathematical modelling as there is considerable lowseparation in the impeller blading [2, 3, 4].Analytical models

donotdescribe thelowcharacteristics fullyas theyarebasedon simpliied assumptions and experimental correction factors[5,6,7].Theprevious theories relyonassumptionsnotbased

on detailed measurements or rigorous CFD calculations. The

maincharacteristicofsuchpumpsistheabilitytogeneratehigh

dischargepressuresatlowlowrates.Althoughthepumphasotheradvantagesthemainlimitationis its inherentlackofhydraulic

eficiency,typically35-50%.TheaimoftheprojectwastouseCFDtooptimisethebladeproilestoincreasetheeficiencyofthepumpandCFDisarobustmethostoobtaindata

NotwithstandingCFDbeingrecognisedasagooddesigntool

in the initial design stage, the computational results must be

validatedwithexperimentaldata.Itisthereforecriticaltohave

accesstomanufacturingmethodsthatcanproducedimensionally

accurate,smallandcompleximpellersthatarerobustenoughfor

testing. Prototypes this complex would normally be machined

usingcomputernumericalcontrol(CNC)machiningtechniques.

ig.1: Regenerative Pump Impeller

ig.2: Chevron Proile Regenerative Pump Impeller

Development of a Regenerative Pump Impeller

Using Rapid Manufacturing Techniques

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FrancisQuail,ThomasScanlon,MatthewStickland

francis.quail@strath.ac.ukmatt.stickland@strath.ac.uktom.scanlon@strath.ac.uk

DepartmentofMechanicalEngineering,StrathclydeUniversity,JamesWeirBuilding,75MontroseStreet,Glasgow,G11XJ,

UnitedKingdom

Having produced the standard radial impeller using

conventional milling techniques, ig. 1, to modify the bladeproiles presents a considerable challenge even for the mostskilledoperators.Thecomplexityofthemodiiedbladeproiles,showninig.2,wouldnormallynecessitatetheuseofexpensiveCNCmachineswith5-axiscapability.Thispaperinvestigatesan

accurate alternativemanufacturing technique to create suitable

impeller prototypes rapidly and cost effectively for use in

experimentsduringtheCFDevaluationprocess.Thechallenge

ofthisprojectwasnotonlytodevelopaCFDmodeltorepresentthe complex luid motion within the pump but also a robustmanufacturingprocesstoproducethecomplexoptimisedblade

designsneededforvalidationtesting.

InthisworktheresultsoftheCFDmodellingarecompared

toexperimentaldatacarriedoutbytheauthors.Whencorrectly

applied CFD, allows the user to study the low patterns in aregenerative pump and verify this with empirical test data.

The key technologies of rapid manufacturing (RM) are rapid

prototyping(RP)andrapidtooling(RT).RPisatechnologyfor

quick fabrication of physical models or functional prototypes

directly fromcomputer aideddesign (CAD)data.RT involves

theproductionofmouldsandtoolinginsertsusingRP.

EXPERIMENTALPROCEDURE

The experimental rig was a closed loop arrangement where

ahead tankcontains theworkingluidwhich in this casewaswater.The pump itself was driven by a 3kW induction motor

to operate at a constant speed of 3000 rpm. The motor was

connectedtoadynamometercontainingaloadcelltoaccurately

measure the input torque to the impeller for calculating the

pump eficiency.Theluidlowratewas determined by alowcontrolvalvemeteringthelowtoadegreenecessarytoproducearunningcharacteristic.Thisallowedarangeofpossiblelowstobemeasuredusingahalleffectturbinelowmeterataconstantrunningspeed(ig.3).Thetestprocedurewastomeasureinputpower,suctionpressure

and discharge pressure over a range of lowrates. The testimpellerwasa30bladedimpellerofwidth1.3mmanddiameter

74.5mm.Theimpellerwasadoublesuctionshapedesignedwith

alignmentof theblades tobalance axial thrust (ig. 4). In thisdesigntheimpellerhadradialteethorvanesmachinedintoeach

sideatitsperiphery.

Theluidenteredbothsidesoftheimpellerthroughasuctionportmakingtheunitadoublesuctionunit.Thecasinghadabarrier

wall “stripper” through which the impeller passes with close

clearance (ig. 4).The stripper seperateslowbetween suctionanddischargeandthelengthofthisbarrierwasequaltoatleast

twobladepitches.Theanglebetweentheinletandoutletports,

knownas the“stripperangle”,was30° in the testcase.When

thestripperangleissmall,moreworkisdoneontheluidduetotheincreasedpumpingregion,buttheleakagelowthroughthestrippergapfromtheoutlettoinletisincreased.

ig.3: Regenerative Pump Rig Schematic

DESIGNOFTHEREGENERATIVEPUMPIMPELLER

The regenerative pump uses an impeller with Turbine-type

bladesmountedontheperipheryrunninginanannularchannel

surroundingtheperipheryofthewheel.Inthedesign,theimpeller

hasradialteethmachinedintotheimpellerperipheryandtheluidpassesthroughanopenannularchannelandcirculatesrepeatedly

throughtheimpellervanes.(igs.1,4)

ig.4: Regenerative Pump

INLET

STRIPPER

OUTLET

The regenerative pump is sometimes also referred to as

a peripheral pump, turbulence pump, friction pump, turbine

pump,dragpump,sidechannelpump,tractionpumporvortex

pump.Therepeatedluidcirculationduringthelowprocessor‘multistaging’principallyallowsregenerativepumpstogenerate

highheadsatrelativelylowspeciicspeeds.Inspiteofhavingoperatingcharacteristicsthatmimicapositive

displacementpump,(powerdirectlyproportional tohead,with

maximumpowerrequiredatshutoff,andasteephead-capacity

curve),theregenerativepumpisakineticpump.Thatiskinetic

energyisimpartedtotheluidbytheseriesofimpulsesgiventotheluidbytherotatingimpellerblades.Theregenerativepumpwilldevelopsigniicantlyhigherheadsthanacentrifugalpumpwiththesamesizeimpeller.[8,10,11]

It is essential tohaveaccess tomanufacturingmethods that

can produce dimensionally accurate, small and complex parts.

Having determined that the baseline radial impeller (ig. 1),withparallelbladesurfaces,wasthelimitofoperatorcontrolled

milling techniques, an alternative approach was required to

facilitatetheproductionofincreasedcomplexityvariantsofthis

standard. (ig. 2)The need is to consider a faster and cheaperprocess toproduceprototypes.Ananswer to thisneed is rapid

prototyping.

Previousmeansofproducingaprototypetypicallytookman-

hours,manytools,andskilledlabour.Forexample,drawingswere

senttoskilledcraftsmenwherethedesignonpaperwasfollowed

andathree-dimensionalprototypewasproducedinwood.This

typicallywasnotaspeedyprocesswithhighskilledlabourcosts.

Thecomplexityofthebladeproiles,needforstrength,accuracy/surfaceinish,qualitywhilstconsideringtherelativesizepresentproblemsinthisapproach.

MANUFACTURING

Fabricationwithrapidprototypingmethodsmaybedivided

broadly into those involving the addition or the removal

ofmaterial.

Inthispaper,RPsystemsareconsideredtobuildprototypes

fortheregenerativepumpimpellerusing4axismillingmachine,

3D printing, fused deposition modelling (FDM) and FDM

inconjunctionwithRTVprocess(vacuumforming).RP is an acronym for Rapid Prototyping while SRP is an

acronym forSubtractiveRapidPrototyping.SubtractiveRapid

Prototyping is used to describe traditional CNC cutting where

generallymaterialisremovedfromasolidblockwitharotating

cutter. In the strictest sense Rapid Prototyping applies to both

additiveandsubtractiveprocessessincebothcreateprototypes

inarelativelyrapidfashion.Inrecentyears,RapidPrototyping

hasgenerallyreferredtotheinnovativeadditiveprocesseswhich

buildamodeluponelayeratatime.Thisadditiveprocessallows

thecreationofextremelycomplexpartsthatcannotbeproduced

bytraditionalSubtractiveRapidPrototypingmachines.RPparts

are generally created as conceptual models for designers and

manufacturerstoevaluateattheproductdevelopmentstageRM

partsareusuallymadeforinclusioninainishedproduct.Theirstmethodconsideredproducingthebladeswaswith

4 axis CNC. CNC machines can exist in virtually any of the

forms of manual machinery, like horizontal mills. A 4th axis

allows rotation of machine parts. The part can be machined

and then rotated, or continuously spun as it is machined.

ThemostadvancedCNCmilling-machines,the5-axismachines,

addtwomoreaxesinadditiontothethreenormalaxes(XYZ).

Theifthaxis(Baxis)controlsthetiltofthetoolitself.(ig.5).Inthecaseoftheregenerativepumpimpellertheset-upandixturedificultiesparticularlyfor10ormorebladeconigurationswasconsidered.

ig.5: CAM tool path plot of Impeller

Asseen inig.6, the Impellerwouldhave tobe turnedandreixed to allow symmetric machining. The geometry of theimpellers thatwere assessed containeddificult overhangs andinteriorvolumes(betweenblades), thatprovedproblematicfor

thefouraxismachines.Theneedtomachinealongasplit line

then,turnthecomponentandcontinuemachiningwouldintroduce

repeatabilityandallignmentissuesfortheoperator.Thiswould

increasemanufacturing time and be a source of possible error

andwashencediscountedasaproductionmethod.[ig.6]

ig.6: CAM tool split line plot of Impeller

The next category to be considered was 3D printing rapid

prototyping technology.A three dimensional object is createdby layering and connecting successive cross sections of

material. 3D printers are generally faster, more affordable

and easier to use than other additive fabrication technologies.

Layers of a ine powder (plaster, corn starch, or resins) areselectively bonded by “printing” an adhesive from the inkjetprinthead in the shape of each cross-section as determined

byaCADile.(igs.7,8)

ig.7:3D -Printer

ig.8: Bonded Shape Impeller Lay down

ig.9: 3D Impeller

Theinishedprintedimpelleristhencoatedwithaniniltrationmaterial to prevent the fragile structure from crumbling.

(ig.9).Evenaftercoatingthespecimenprovedtoofragiletotestintheexperimentalrig.

The next process to be considered was fused deposition

modelling.(FDM)systemsconsistoftwomovableheads(onefor

buildingthepartandoneforthesupports)whichdepositthreads

ofmoltenmaterialontoasubstrate(ig.11).Thematerialisheatedjustaboveitsmeltingpointsothatitsolidiiesimmediatelyafterextrusionandcold-weldstothepreviouslayers.Whentheirstlayer is complete, the platform lowers by one layer thickness

and theprocessbeginsagain.Thepart iseasily removedfrom

theplatform,supportsare removedand thespecimen is ready.

(ig.10)

ig.10: FDM Completed Impeller

The technology was developed by S. Scott Crump in the late

1980s and was commercialised in 1990. The FDM technology

is marketed commercially by Stratasys, which also holds

a trademark on the term. [9]

ig.11: FDM Machine and completed Impeller

Severalmaterialsareavailablewithvaryingtrade-offsbetween

strength and temperature. As well as acrylonitrile butadiene

styrene(ABS)polymer, theFDMtechnologycanalsobeused

with polycarbonates, polycaprolactone, polyphenylsulfones

andwaxes.A“water-soluble”materialcanbeusedformaking

temporarysupportswhilemanufacturingisinprogress.Marketed

under the name WaterWorks by Stratasys this soluble support

material is actually dissolved in a heated sodium hydroxide

solutionwiththeassistanceofultrasonicagitation.[9]ABS,(C8H8·C4H6·C3H3N)n,isacommonthermoplasticused

tomakelight,rigid,moldedproductssuchgolfclubheads,(dueits

goodshockabsorbance).Itisacopolymermadebypolymerizing

styreneandacrylonitrile in thepresenceofpolybutadiene.The

proportions can vary from 15 to 35% acrylonitrile, 5 to 30%

butadieneand40to60%styrene.TheadvantageofABSisthat

thismaterialcombinesthestrengthandrigidityoftheacrylonitrile

and styrenepolymerswith the toughnessof thepolybutadiene

rubber.The most important mechanical properties ofABS are

resistanceandtoughness.Avarietyofmodiicationscanbemadetoimproveimpactresistance,toughness,andheatresistance.The

impactresistancecanbeampliiedbyincreasingtheproportionsof polybutadiene in relation to styrene and also acrylonitrile

althoughthiscauseschangesinotherproperties.

ADVANTAGESANDDISADVANTAGESOFTHERPPROCESSES

The FDM part was produced and run on test. However the

impeller blades broke apart and after close inspection it was

observed that theextrudedmaterialhadsmallvoidsacross the

bladethickness.Thiswasduetoinsuficientmateriallaydownasaresultoftherelativebladesize.(ig.12)

Oftheprocessesdescribed,onlytheFDMprocesswasableto

produceaspecimenfordirectuse.

ig.12: Failed FDM Impeller

To produce a mechanically stronger impeller FDM in

conjunction with RTV was considered. RT as previouslymentioned involves the production of moulds and tooling

inserts using RP. Room temperature vulcanizing (RTV) is

a relatively inexpensive and fast way to fabricate prototype

or pre-production tools. RTV tools are also known as silicone

rubbermoulds.ThemostwidelyusedformofRTVmouldingis

vacuumcasting.(ig.13)

Therangeofmaterialswithimprovedstrengthcharacteristics

andtheabilityofbetterillingoftheimpelllerproiletopreventvoidsincreaseswithRTV.Aporousorventedmoldisusedand

isplacedonatableorcontainerwherevacuumisapplied.The

liquid to be cast will be driven into the mold by atmospheric

pressure, while the vacuum will also remove trapped air that

would otherwise impede the free low of the liquid castingmaterial.

ig.13: RTV mould containing Impeller

Vacuum Casting is widely used for producing accurate

silicone tools for casting parts with ine details and very thinwalls. Vacuum castings are precise replicas of the patterns,

dimensionallyaccuratewithoutblemisheswithallproilesandtexturesfaithfullyreproduced.

Themaindificultytillthispointhadbeenproducingimpellerswithsuchsmalldimensionsthatcouldbeproducedmechanically

strong enough to survive the luid loading within the runningpump.

The vacuum casting process includes the following main

steps:

ig.14: FDM pattern

TheirststepistoproduceapatternusinganyoftheavailableRPprocesses(FDMinthiscase)(ig.14)

ig.15: Gated / vented blade.

The impeller blade with a chevron proile shown here, isprepared by adding venting and gating to the pattern; this is

neededasthevacuumisimposedduringcastingtoallowairto

escape(ig.15).

ig.16: Suspension and parting

Thepatternisitwithacastinggateandsetuponthepartingline,andthensuspendedinamouldcastingframe.Thepattern

needstohaveadequatemouldmaterialonallsidesandstillhave

thepartinglineidentiiedtofacilitateremoval(ig.16).

ig.17: Mould pouring

Once the two-part silicone-rubber is de-aerated and then

mixed, it is poured into the mould casting frame around the

pattern.(ig.17)

ig.18: Pattern removal

After curing the mould inside a heating chamber; the next

stage is the removalof thepattern fromthesiliconemouldby

cuttingalong theparting lineand thenclosingand sealing the

mould;(ig.18)Thecomputer-controlledequipmentmixesandpourstheresin

inside the vacuum chamber.As this takes place in a vacuum,

themouldisilledcompletelywithoutleavinganyairpocketsor

voids.TheMCPvacuumcastingrequiresinitialinvestmentina

vacuumchamberwithtwosections.

ig.19: Vacuum casting Impeller

Theuppersectionisformixingtheresinandthelowerisfor

castingtheresinintothemould.(ig.19)

ig.20: Impeller mould

Aftercuringthepartinaheatingchamberfor2–4hoursand

then removing it from the mould.After casting the resin, the

mouldismovedtotheheatingchamberforbetweentwotofour

hourstocuretheurethanepart.(ig.20).

ig.21: Removing gate risers

Thegateandrisersareremovedfromthecastingtomakean

exactcopyofthepattern.Afterhardening,thecastingisremoved

fromthesiliconemould.(ig.21)The introduction of RT technology enabled prototype,

pre-productionandinsomecasesfullproductiontoolingtobe

fabricatedwithsigniicantlyreducedtimeframes.

ÁUpperSection

ÁLowerSection

RESULTS

The success of the methodology has lead to further more

complexbladeproilesbeingassessed in theexperimental testprocedure.

Rapidprototypingtechniquesareextremelyusefulinhelping

thepumpdesignertoconductpreliminarytestingonalow-cost

prototype.Basedontheresultsobtained,theabilitytomodifyor

improvethedesignsbeforeresortingtomorecostlyfabricating

methods has proved extremely beneicial in this currentresearch.

TheresultshaveshownthatFDM/RTVisaviableandfeasible

methodofproducingprototypesfortesting.Furtherreinementsofthetechniquearecurrentlybeingpursuedsothatthesurface

inish,isenhancedwhilstmaintainingtheaccuracyofthepartsproduced.

Preliminary results demonstrate that the impellers have the

potentialtoimprovethepumpeficiency.

ig.22: Regenerative Pump Results

Whilst the process has demonstrated reasonable success in

producing viable test samples, theFDM/RTVmethod several

disadvantages. Surface inish and the need for a two stagemanufacturing process (FDM then RTV). Limited range of

materials availablemeant that a newmethodof photopolymer

setting will be considered in the future.This will increase the

rangeofmaterialsforselection,improvesurfaceinishanddeletetheneedtouseRTV.

The helical motion of the luid within the pump is bestprescribed by low visualisation work carried out in the1940’sand1950’s.[4,8,10]Theworkpresentedinthispaperdemonstrates interesting correlation to these observed tests in

awaythathasn’tbeenachievedmathematicallytodate.

However the results achieved using the FDM/RTV

methodology have successfully lead to the optimisation of the

pump in an effective manner. (ig. 22)

CONCLUSIONS

There are a number of conclusions which may be drawn

with regard to effectively matching the regenerative pump

CFDmodelwith theexperimentaldata.CFDresultsproduced

areasonablerepresentationof thelowinaregenerativepumpandarebeingutilisedtofocusinvestigationforunitperformance

improvement (ig. 22).As the capabilities ofCFDcontinue todevelop,itistobeexpectedthattheuncertaintiesassociatedwith

CFDpredictionshouldalsoreduce.Attheveryleastitistobe

expected that there will be a continuing growth in processing

powerfortheforeseeablefuture,whichwillreduceandperhaps

remove the geometric simpliications which have to currentlybe made. The ability to test and validate the models is only

possible through detailed experiments. This work has been

usefultonotonlybenchmarkcurrentregenerativepumpdesign,

butgivesconidenceintheabilityofCFDoptimisationforthedesign to increase the performance of the pump in the future

[12,13,].Theindingsofthisoptimisationworkwillbepresentedin a future paper. The remarkable increase in the number of

commerciallyavailableRPandRTsolutionssincethe1990sbyadvancesinthree-dimensionalCADmodelling,computeraided

manufacturing,computernumericalcontrolandthedevelopment

ofnewmaterials,arethereasonthisworkproceeds.

ACKNOWLEDGEMENTS

TheauthorswouldliketoexpressgratitudetoMr.DrewIrvine,

Mr.TomFarmer,Mr.DuncanLindsayandMr.DaveCunningham

for their help and assistance in the impeller manufacturing

processes.

REFERENCES

1. EUROPEAN PARLIAMENT. “Establishing a framework

for the settingofecodesign requirements forenergy-using

products”,DIRECTIVE2005/32/EC(2005)

2. BADAMI, M: “Theoretical and experimental analysis oftraditional and new peripheral pumps” SAE Technical

PapersSeries,No971074(1997)3. ENGEDA,A.: “Flow analysis and design suggestions for

regenerative low pumps” ASME FEDSM2003-45681(2003)

4. ENGELS, H.: “Untersuchungen an Ringpumpen ”, TechHochHannover.1(1940)

5. RAHEAL,M.,ENGEDA,A.,:“Systematicdesignapproachfor radial blade regenerative turbomachines” Journal for

PropulsionandPowerVol.21(2005)

6. SENOO,Y“TheoreticalresearchonFrictionPump”Institute

ofFluidEngineeringVol5No1pp23-48(1948)7. SONG, J. W., ENGEDA, A., CHUNG, M.K, “Modiied

theoryforthelowmechanisminaregenerativelowpump”ProceedingsIMECHE,Vol217(2003)PowerandEnergy

8. WILSON, W.A., SANTALO, M.A., OELRICH, J.A.: “ATheory of the luid dynamic mechanism of regenerativepumps”Trans.ASMENo.8(1955)

9. STRATASYSWebpage,StratasysInc.,EdenPrairie,min-

nesota,2001,www.stratasys.com

10. IVERSON, H.W.: “Performance of the Periphery Pump”–ASMEVol7pp19-22(1955)

11. MEAKHAIL, T., PARK, S.O,.: “An Improved theory forregenerativepumpperformance.”IMECHEVol219PartA(2005)

12. SHIH,T.H., LIOU,W.W., SHABBIR,A.,YANG, Z., and

ZHU, J., , “A New k-ε Eddy-Viscosity Models for High

Reynolds Number Turbulent Flows-Model Development

and Validation”, Computers Fluids, 24 (3), pp. 227-238.

(1995)13. SPALART, P., “.Trends in turbulence treatments” .AIAA

paper(AIAA2000-2306)(2000)

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