Introduction To Tribology, Rotordynamics & Lubricated

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August 2020Introduction totribology,rotordynamics &lubricated elementsDr. Luis San AndresMast-Childs Chair ProfessorTurbomachinery LaboratoryTexas A&M UniversityLsanandres@tamu.edu1

Tribology?What is it for? Will I ever use it?2

Tribology embodies the study offriction, lubrication and wear.and involves mechanical processes (motion & deformation).A tribologist performs engineering work to predict andimprove the performance (how much) and reliability (forhow long) of a mechanical system.Fluid mechanicsMaterial scienceTribologySolid mechanicsManufacturing3

Tribology – Some Applications TodayExo-skeletons & sports equipmentcompliant, durable, tough, better performance(less friction and less wear)Medicine:Hip-joint replacements,miniature pumps for fluid injection/removal,heart pumps and implants,1 MRPM dental hand drillsUltra-hard drilling equipment:no wear and tear, i.e. infinite g,materials, 3D printSolid lubricants.GashydrodynamicsSolid lubricants(coatings)Surfaceengineering4

Dr. San Andres movesfrom beinga pain in the neck to being screwed to beingcrushedFriction, lubrication & wearIs the order important?5

Turbomachinerytoday& tomorrow6

TurbomachineryA rotating structure where the load or the driverhandles a process fluid from which power isextracted or delivered to.Fluid film bearings (typically oil lubricated) supportrotating machinery, providing stiffness and damping forvibration control and stability.In a pump or a compressor, neck ring seals and interstage seals and balance pistons also react with dynamicforces. Impellers also act to impose static and dynamichydraulic forces.Acceptable rotordynamic operation ofturbomachinery:Ability to tolerate normal (even abnormal transient)vibrations levels without affecting TM overall performance(reliability and efficiency)7

PV/CV turbochargersw/w/Fully Floating Bearing Semi Floating BearingThe future todayw/Ball Bearing8

Centrifugal compressorWhere are the bearings?and the seals?9

Gas turbineWhere are the bearings?and the seals?10

SSME turbopumpsWhere are the bearings?LH2and the seals?LOX11

st21centuryturbomachinery12

21st century turbomachineryUltra-performance (reinjection)compressors: 15,000 psi (1,000 bar)Combined cycle turbines (gas/steam):Concentrated solar power: sCO2efficiency 60%Aircraft: Larger high-bypass geared turbofans (GR 5)Electric distributed propulsion systemsGTs batteries electric fans for thrustLarger efficiency & lower noise. Braking regenerative powerUnmanned Aerial Vehicles (Drones):war at a distance &w/o casualties,surveillance, parcel mail delivery, crop fumigation, archeologySmart engines and structures:control of surge and stall in compressors,elimination of Noise & Vibes with configuration changesReusable rocket engines:LH2 and LOx with fluid film bearingsRotordynamics,materials, seals,extreme environmentscomposite materials,coatings,extreme environmentsRotordynamics,Electronics,Materials & Coatings,SFDsE-motors, materials,3D printing,controls andelectronics.Materials,3D printingrotordynamics13

Subsea pumping & compressionHigh pressures & extreme temperaturesSubsea Engineering or SURF –SubseaUmbilicalsRisers)Wet compression systemsmust be reliable (5 y operation)FlowlinesMeso-micro turbomachinery:portable packs (5 kW), 1 million rpmOil-free gas turbines and generators:(mid size to 0.5 MW): foil gas bearings, damper seals.Rotordynamics,3D printing,materialscoatings: solid lubesgas lubrication &rotordynamics14

Microturbomachinery needs & hurdlesLargest power to weight ratioCompact & low # of partsHigh speedReliability and efficiencyLow maintenanceMaterialsExtreme temperature andpressure – multiple phasesManufacturingRotordynamics &(Oil-free) Bearings & SealingCoatings: for low friction and wearCeramic rotors and componentsAutomated agile processesAdditive manufacturing: & #Environmentally safe(low emissions)Lower lifecycle cost ( kW)Processes & CyclesLow-NOx combustors for liquid &gas fuels. Scaling to low Reynolds #FuelsBest if free (bio-fuels)15

H2 Fuel Cell Electrical VehiclesOil-free system offers higher efficiency and power density.Rotor supported on gas bearingsCompressed airblows into Fuel Cell stackFuel cell stack*Photos from SAE Int. J. Alt. Power 2016 and EHEC 2018Air compressorEfficient FCEV!!16

PV turbocharger systemHoneywell (2007)Borg & Warner (2012)conventionalOil-BearingFoil BearingschosenHybrid vehicles: 50 miles/gal & 0 NOx fuel cells.Issues are high temperature, materials and NL rotordynamics17

Application of Meso/MEMS MTMRescueRobotPortable GeneratorMicro Gas TurbinePOWER DENSITY (MW/m3)5000http://www.robhaz.com/50050Large ScaleCombustorhttp://www.mdot.com/page8.htmlMicro ReactorMobileelectronicequipmentCombustorLiSO2 Battery(BA5590)5Solar s.com/products.php4Large ScaleMicro Solar Cell0.5http://www2.northerntool.com/product/448 448.htmhttp://www.notebookhttp://www.w review.com/irefly.com/1001000SIZE .htm 18

Fluid FilmBearings19

Fluid Film BearingsFluid film bearings produce low friction between solidsurfaces in relative motion and generate a load supportfor mechanical components.The lubricant or fluid between the surfaces may be a liquid,a gas or even a solid (coating).Fluid film bearings, if well designed, support static anddynamic loads, affecting the dynamic performance ofrotating machinery.Basic operational principles arehydrodynamic, hydrostatic or hybrid(a combination of the former two).20

Bearings: Friction and LubricationBearings enable smooth (low friction) motion between solid surfaces inrelative motion and, if well designed, support static and dynamicloads. Bearings affect the dynamic performance of machinery(reliability and availability).FrictioncoefficientFull filmlubricationSurface velocity x viscositySpecific pressure21

Hydrodynamic BearingsHydrodynamic pressure generated by relative motion between twomechanical surfaces with a particular “wedge like” shapeAdvantagesPressureDo not require external source ofpressure. Fluid flow is dragged intothe convergent gap in the directionof the surface relative motion.Support heavy loads. The loadsupport is a function of thelubricant viscosity, surface speed,surface area, film thickness andgeometry of the bearing.Long life (infinite in theory) withoutwear of surfaces.Provide stiffness and dampingcoefficients of large er bearingSchematic view ofhydrodynamic (selfacting) fluid film bearing22

Hydrodynamic l effects affect performance iffilm thickness is too small or availableflow rate is too low.Require of surfaces’relative motion toRelativemotiongenerate load support.Induce large drag torque (power losses)and potential surface damageat start-upHydrodynamic(before lift-off) and touch down.wedgePotential to induce hydrodynamicinstability, i.e. loss of effective dampingSlider bearingfor operation well above critical speed ofrotor-bearing systempressurePlain journalbearingSchematic view ofhydrodynamic (self-acting)journal bearing23

Examples of hydrodynamic bearingsPARTIAL ARCJOURNAL BEARINGFLOATING RINGJOURNALBEARINGDamTop halfBottom halfGroovePRESSURE DAM JOURNAL BEARINGTilting padbearingsTypical cylindrical journal bearings24

Hydrostatic BearingsExternal source of pressurized fluid forces lubricant to flow between twosurfaces, thus enabling their separation and the ability to support aload without contact.AdvantagesSupport very large loads. The loadsupport is a function of the pressuredrop across the bearing and the area offluid pressure action.Load does not depend on film thicknessor lubricant viscosity.Long life (infinite in theory) without wearof surfacesProvide stiffness and dampingcoefficients of very large magnitude.Excellent for exact positioning andcontrol.Schematic view ofhydrostatic/ hydrodynamicjournal bearing25

Hydrostatic BearingsDisadvantagesRequire ancillary equipment. Largerinstallation and maintenance costs.Need of fluid filtration equipment. Loss ofperformance with fluid contamination.recessPenalty in power consumption: pumpinglosses.Limited LOAD CAPACITY f(Psupply)fluidjournalPotential to induce hydrodynamicinstability in hybrid mode operation.Potential to show pneumatic hammerinstability with compressible fluids, i.e. lossof damping at low and high frequencies ofoperation due to compliance and time lagof trapped fluid volumesFlowsupplyat PsorificeSchematic view of hydrostatic/hydrodynamic journal bearing26

Squeeze Film DampersNormal surface motions can alsogenerate hydrodynamic pressures inthe thin film separating two surfaces.The squeeze film action workseffectively only for compressiveloads, i.e. those forcing the approachof one surface to the llbearinghousingSqueeze film dampers areroutinely used to reduce vibrationamplitudes and isolate structuralcomponents in gas jet engines,high performance compressors,and occasionally in water pumps.Typical squeeze film damper (SFD)configuration27

Annular Pressure SealsSeals (annular smooth, labyrinth or honeycomb) separate regions of highpressure and low pressure and their principal function is to minimize theleakage (secondary flow); thus improving the overall efficiency of a TMextracting or delivering power to a fluid. Seals have larger clearances than loadcarrying bearings.Flow ofprocess fluidStatorHighPressureLowPressureRotorLABYRINTH SEAL on ROTOR ODInter-stage sealImpeller eye orneck ring sealBalance piston sealSeals in a Multistage Centrifugal Pump or Compressor28

Annular Pressure SealsStraight-Through and Back-to-back Compressor Configurations and 1st Mode ShapesDue to their relative position within a rotor-bearing system, sealsmodify sensibly the system dynamic behavior. Seals typically"see" large amplitude rotor motions. This is particularlyimportant on back-to-back compressors and long-flexiblemultiple stage pumps.29

Damper SealsHole-Pattern SealRound hole-patternsealUHoneycomb SealUnwrapFigure 3: Honeycomb seal for turbopumpSurface textured seals for turbopumpsLabyrinth SealIntentionally roughened stator surfaces (macro texturing) reduce theimpact of undesirable cross-coupled dynamic forces and improve sealstability.Annular seals acting as Lomakin bearings could be support elements(damping bearings) for cryogenic turbopumps as well in process fluidpumps & high pressure compressors30

Seals in a high pressure steam turbineWhere are the seals?31

Seals in an Intermediate pressure steam turbine32

ME626 Course Objectives1. To learn about the physical concepts and mathematical models forthe analysis and design of fluid film bearings and seals.2. To acquire knowledge based on the detailed review of the literatureon fluid film lubrication and rotordynamics.3. To identify the mechanical effects of importance on the static anddynamic forced performance of fluid film bearings.4. To learn about the effects of fluid film bearings on the rotordynamicsof turbomachinery.5. To identify the future trends in applications of bearing and sealtechnologies and the needs for further research.6. To provide the basics of efficient computational skills for theprediction of the static and dynamic forced performance of fluid filmbearings.33

LEARN MORE AT http://rotorlab.tamu.eduQuestions (?)Luis San Andres Texas A&M University 202034

Introduction to tribology, . Tribology? 3 Tribology embodies the study of friction, lubrication and wear. and involves mechanical processes (motion & deformation). A tribologist performs engineering work to predict and improve the performance (how much) and reliability (for

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