1、主讲人：XXXFluent对旋转式动力机械的分析 Fluent Inc.7/19/20222Fluent Software TrainingUGM 2001Introduction to Rotating Machinery Analysis Using Fluent Frank KelecyFluent Inc.Fluent Inc.7/19/20223Fluent Software TrainingUGM 2001AgendauIntroductionuSingle moving reference frame(SRF)model uMultiple moving reference fr
2、ame(MRF)modeluMixing plane modeluSliding mesh modeluQuestions?Fluent Inc.7/19/20224Fluent Software TrainingUGM 2001MotivationuFlows involving rotating domains occur frequently in engineeringuExampleslcompressors and turbineslfans and pumpslrotating cavities,seals,and bearingslmixing equipmentlfluid
3、coupling devices and torque converterslair motorslmarine and aircraft propellersland many moreuComputational Fluid Dynamics(CFD)today plays a central role in the design and analysis of rotating machinery Fluent Inc.7/19/20225Fluent Software TrainingUGM 2001Examples of Rotating Machinerygas turbine e
4、ngineautomotive water pumptube axial fansteam turbineHVAC blower unithydro turbine Fluent Inc.7/19/20226Fluent Software TrainingUGM 2001Goals of the TraininguProvide an introduction to rotating machinery modelinguExamine the four major classes of rotating machinery problemslSingle rotating reference
5、 frame(SRF)lMultiple rotating reference frame(MRF)lMixing planelSliding meshuPresent details on modeling rotating machinery problems using FluentlModel setuplSolution process(steady-state and unsteady)uAnswer your questions!Fluent Inc.7/19/20227Fluent Software TrainingUGM 2001Types of Rotating Machi
6、nery uIn this course,we will classify rotating machinery as follows:lTurbomachinery-machines which add work to or extract work from a fluidncompressors,fans,pumps-add work to achieve a pressure rise in the fluidnturbines,windmills-extract work from fluid to drive other machines lMixing equipment-mac
7、hines which are designed to mix fluid(and possibly solid)materials for use in a chemical processing applicationnindustrial mixing tanks lRotating tanks,seals,cavities,and other devicesndisk cavities and labyrinth seals in gas turbine enginesnelectric motor cooling passagesndisk drivesnrotating tires
8、 on automotive vehiclesuAll of these applications involve rotating surfaces and domains(and thus may use a rotating reference frame for modeling)Fluent Inc.7/19/20228Fluent Software TrainingUGM 2001Classification of Turbomachinery uAxial machineslFlow through the machine is(in general)aligned with t
9、he axis of rotationlExamples:propellers,axial fans/compressors/turbines,swirlers uCentrifugal machineslFlow through the machine is(in general)perpendicular to the axis of rotationlExamples:liquid pumps,centrifugal fans/compressors,radial turbinesuMixed FlowlFlow through the machine is somewhere betw
10、een axial and centrifugallExample:mixed flow compressor Fluent Inc.7/19/20229Fluent Software TrainingUGM 2001Basic Problem StatementuWe wish to solve for the flow through a domain which contains lrotating componentsnpropeller,compressor/turbine blade,radial impeller,etc.lstationary and/or rotating s
11、urfacesnducts walls,bores and cavities,seal teeth surfaces,etc.uRotation(s)assumed to be steadylaccelerating reference frames can be modeled with source terms(not considered here)uWell-posed boundary conditionslflowrates,pressures,temperatures,other scalars at inlet/outlet boundarieslwall motion,the
12、rmal,other BCs at wallsuOther considerationsllaminar/turbulent flow,other physics(e.g.multiphase flow,heat transfer)llevel of interaction between moving/stationary components Fluent Inc.7/19/202210Fluent Software TrainingUGM 2001Modeling ApproachesuSingle Rotating Frame(SRF)lEntire computational dom
13、ain is referred to rotating reference frameuMultiple Rotating Frame(MRF)lSelected regions of the domain are referred to rotating reference frameslIgnore interaction effects steady-stateuMixing Plane(MPM)lInfluence of neighboring regions accounted for through use of a mixing plane model at rotating/s
14、tationary domain interfaceslIgnore circumferential non-uniformities in the flow steady-stateuSliding Mesh(SMM)lMotion of specific regions accounted for by mesh motion algorithm lFlow variables interpolated across a sliding interfacelUnsteady problem-can capture all interaction effects with complete
15、fidelity Fluent Inc.7/19/202211Fluent Software TrainingUGM 2001Single Reference Frame(SRF)Modeling Fluent Inc.7/19/202212Fluent Software TrainingUGM 2001Introduction to the SRF ModeluMany problems which involve rotating components can be modeled using a single rotating reference frame.uWhy use a rot
16、ating reference frame?lFlowfield which is unsteady in the stationary frame becomes steady in the rotating framelSteady-state problems are easier to solve.nsimpler BCsnlow computational costneasier to post-process and analyzeuWe will discuss issues related to SRF modeling in this section,but many con
17、cepts(e.g.solver settings,physical models,etc.)will also apply to MRF,mixing plane,and sliding mesh modeling.Fluent Inc.7/19/202213Fluent Software TrainingUGM 2001Illustration of SRF modelbladehubdomainrotatingreferenceframeaxisshroud/casing Fluent Inc.7/19/202214Fluent Software TrainingUGM 2001Impl
18、ications of SRFuSingle fluid domainuDomain rotates with a constant rotational speed about a specified rotational axislEntire domain moves with the reference frameuBoundaries which move with the fluid domain may assume any shapeuBoundaries which are stationary(with respect to the laboratory or fixed
19、frame)must be surfaces of revolutionuCan employ rotationally-periodic boundaries for efficiency(reduced domain size)Fluent Inc.7/19/202215Fluent Software TrainingUGM 2001Stationary Walls in SRF Modelsstationary wallrotorbaffleCorrectWrong!Wall with baffles not a surfaceof revolution!Fluent Inc.7/19/
20、202216Fluent Software TrainingUGM 2001N-S Equations:Rotating Reference FrameuTwo different formulations are used in FluentlRelative Velocity Formulation(RVF)nObtained by transforming the stationary frame N-S equations to a rotating reference framenUses the relative velocity as the dependent variable
21、 in the momentum equationsnUses the relative total internal energy as the dependent variable in the energy equationlAbsolute Velocity Formulation(AVF)nDerived from the relative velocity formulationnUses the absolute velocity as the dependent variable in the momentum equationsnUses the absolute total
22、 internal energy as the dependent variable in the energy equation Fluent Inc.7/19/202217Fluent Software TrainingUGM 2001Reference Framesxyzzyxstationaryframerotatingframeaxis ofrotationrCFD domainorR Fluent Inc.7/19/202218Fluent Software TrainingUGM 2001uAssumptionslNo translation()lSteady rotation(
23、=constant)about specified axisnaxis passes through origin of rotating framelIgnore body forces due to gravity and other effectslIgnore energy sourcesuDefinitionslAbsolute velocity()-Fluid velocity with respect to the stationary(absolute)reference framelRelative velocity()-Fluid velocity with respect
24、 to the rotating reference frameu3-D compressible,laminar forms of the equations presented in the following slidesAssumptions and DefinitionsVW0/=dtrdo Fluent Inc.7/19/202219Fluent Software TrainingUGM 2001The Velocity TriangleuThe relationship between the absolute and relative velocities is given b
25、yuIn turbomachinery,this relationship can be illustrated using the laws of vector addition.This is known as the Velocity TrianglerUUWV=VWU Fluent Inc.7/19/202220Fluent Software TrainingUGM 2001Relative Velocity FormulationqwwwpeWteBzpwWtwBypwWtwBxpwWtwWtzvrzyvryxvrxtrtrzvrzzzyvryyyxvrxxx=0(continuit
26、y)(x momentum)(y momentum)(z momentum)(energy)Fluent Inc.7/19/202221Fluent Software TrainingUGM 2001Relative Velocity Formulation(2)=kWwzWjWwyWiWwxWTqRWeekwjwiwWzvrzyvryxvrxtrzyx32323221222(relative velocity vector)(relative total internal energy)(Fouriers Law)(viscous terms)Fluent Inc.7/19/202222Fl
27、uent Software TrainingUGM 2001Relative Velocity Formulation(3)uAcceleration terms due to rotating reference framerWkBjBiBBzyx=2Coriolisaccelerationcentripetalacceleration Fluent Inc.7/19/202223Fluent Software TrainingUGM 2001Absolute Velocity FormulationqvvvpeWteBzpvWtvBypvWtvBxpvWtvWtzvzyvyxvxttzvz
28、zzyvyyyxvxxx=0(continuity)(x momentum)(y momentum)(z momentum)(energy)Fluent Inc.7/19/202224Fluent Software TrainingUGM 2001Absolute Velocity Formulation(2)=kVvzVjVvyViVvxVTqVeekvjvivVzvzyvyxvxtzyx323232212(absolute velocity vector)(total internal energy)(Fouriers Law)(viscous terms)Fluent Inc.7/19/
29、202225Fluent Software TrainingUGM 2001Absolute Velocity Formulation(3)uAcceleration term due to rotating reference frameVkBjBiBBzyx=Acceleration reduces to single term involvingrotational speed and absolute velocity Fluent Inc.7/19/202226Fluent Software TrainingUGM 2001SRF Geometries:2-Du2-D Problem
30、sl2-D planar geometries rotate about axis normal to x-y plane with specified origin(periodic boundaries are permitted)l2-D axisymmetric geometries rotate about the x-axisPlanarAxisymmetricxyx Fluent Inc.7/19/202227Fluent Software TrainingUGM 2001SRF Geometries:3-Du3-D ProblemslUser defines both rota
31、tional axis origin and direction for the fluid domainlPeriodic boundaries permittedoriginrotational axis Fluent Inc.7/19/202228Fluent Software TrainingUGM 2001Choice of SolveruSame considerations for general flowfield modeling apply to SRF solver choicelSegregated Solver:incompressible,low speed com
32、pressible flows nExamples:Fans,blowers,pumpslCoupled Solvers:high speed compressible flows,above Mach 0.3nExamples:high pressure axial compressors,turbines,turbochargersuVelocity Formulation recommendationslUse AVF when inflow comes from a stationary domainlUse RVF with closed domains(all surfaces a
33、re moving)or if inflow comes froma rotating domainnNOTE:RVF only available in the segregated solverlIn many cases,either can be used successfully Fluent Inc.7/19/202229Fluent Software TrainingUGM 2001Boundary Conditions and Physical ModelsuBasic BCs used in SRF analysislFluid BClInflow BCsnPressure
34、InletnVelocity InletnMass Flow InletlOutflow BCsnPressure OutletlWallslPeriodicsuPhysical modelslTurbulence modelslDPMlMultiphase,real gas,heat transfer Fluent Inc.7/19/202230Fluent Software TrainingUGM 2001Fluid BCsuUse fluid BC panel to select rotational axis origin and direction vector for rotati
35、ng reference framelNote:all direction vectors should be unit vectors but Fluent will normalize them if they arentuSelect Moving Reference Frame as the Motion Type for SRFuEnter rotational speedlTranslation velocity set to zero Fluent Inc.7/19/202231Fluent Software TrainingUGM 2001Velocity InletsuUse
36、d for incompressible,mildly compressible flows when inlet velocity is knownuCan specify absolute or relative velocity vector uCan specify vector components in Cartesian or cylindrical coordinatesuFor 2-D,axisymmetric with swirl and 3-D problems you can specify tangential velocity aslocityangular veu
37、ser velocityntialuser tange,=inpinpinpinpVrVV Fluent Inc.7/19/202232Fluent Software TrainingUGM 2001Pressure Inlets(1)uPressure inlets can be used with either incompressible or compressible flows.uDefinition of total pressure depends on velocity formulation and compressibility:12222112121=kktttMkppW
38、ppVppincompressible,AVFincompressible,RVFcompressible,AVF Fluent Inc.7/19/202233Fluent Software TrainingUGM 2001Pressure Inlets(2)uSpecify appropriate total pressure and total temperatureuIf inlet flow is supersonic,specify static pressure such that desired Mach number corresponds to pt/p uSpecify f
39、low direction vectorlCan use Cartesian,cylindrical,or local cylindrical coordinate systemlFrame of flow direction depends on velocity formulation!lYou cannot use a frame of reference for the direction which is different from the velocity formulation Fluent Inc.7/19/202234Fluent Software TrainingUGM
40、2001Mass Flow InletsuPrescribe total mass flow rate or mass flux and total temperature for compressible flowsuTotal pressure“floats”since the mass flow rate is fixeduPermits flow direction specification in absolute frame onlylFluent 6 permits direction specification in Cartesian and cylindrical coor
41、dinates Fluent Inc.7/19/202235Fluent Software TrainingUGM 2001Pressure OutletsuSpecify static pressure at the outletuCan employ a radial equilibrium assumption which computes a radial pressure variation fromThe specified pressure is then assumed to be the hub static pressureRVRp2=Fluent Inc.7/19/202
42、236Fluent Software TrainingUGM 2001BackflowuBackflow occurs when the static pressure in a cell adjacent to a pressure boundary falls below the prescribed boundary pressureuFor SRF problems,the direction of the backflow islnormal to the boundary in the absolute frame if AVF is usedlnormal to the boun
43、dary in the relative frame if RVF is useduRecommendationlAs some backflow may occur during the solution process,prescribe reasonable values for all backflow quantitieslTry to minimize(or eliminate)backflow by extending your outlet boundary further downstream Fluent Inc.7/19/202237Fluent Software Tra
44、iningUGM 2001Wall BCsuWall BCs enforce zero normal velocity at all wall surfaceslno slip(zero velocity)for viscous flowsuFor moving reference frames,you can specify the wall motion in either the absolute or relative framesuRecommended specification of wall BCs for all moving reference frame problems
45、lFor stationary surfaces(in the lab frame)use zero Rotational speed,AbsolutelFor moving surfaces,use zero Rotational speed,Relative to Adjacent Cell Zone Fluent Inc.7/19/202238Fluent Software TrainingUGM 2001Periodic BCsuRotational periodic BCs rely on the rotational axis specification to transfer i
46、nformation correctlyuRotationally periodic boundaries can be used in SRF problems to reduce mesh size provided both the geometry and flow are periodicuNotes:lIf you are using the make-periodic command in the TUI,make sure you set the rotational axis in the Fluid BC panel first before creating the pe
47、riodicslOnce the periodic BCs have been set,perform a grid check to see if the reported periodic angles are correct Fluent Inc.7/19/202239Fluent Software TrainingUGM 2001Turbulence Models for Rotating MachineryModelStrengthsWeaknessesSpalart-AllmarasEconomical(1-eq.);good track recordfor mildly comp
48、lex B.L.type of flowsNot very widely tested yet;lack ofsubmodels(bustion,buoyancy)STD k-Robust,economical,reasonablyaccurate;long accumulatedperformance dataMediocre results for complex flowsinvolving severe pressuregradients,strong streamlinecurvature,swirl and rotationRNG k-Good for moderately com
49、plexbehavior like jet impingement,separating flows,swirling flows,andsecondary flowsSubjected to limitations due toisotropic eddy viscosityassumptionRealizablek-Offers largely the same benefits asRNG;resolves round-jet anomalyRecommended k-model forturbomachinerySubjected to limitations due toisotro
50、pic eddy viscosityassumptionReynoldsStressModelPhysically most complete model(history,transport,and anisotropy ofturbulent stresses are all accountedfor)Requires more cpu effort(2-3x);tightly coupled momentum andturbulence equations Fluent Inc.7/19/202240Fluent Software TrainingUGM 2001DPM Modelingu
