1、ANSYS,Inc.Proprietary 2009 ANSYS,Inc.All rights reserved.WS5-1April 28,2009Inventory#002599Workshop 5Cavitating Centrifugal PumpIntroduction to CFXANSYS,Inc.Proprietary 2009 ANSYS,Inc.All rights reserved.Workshop SupplementWS5:Cavitating Centrifugal PumpWS5-2April 28,2009Inventory#002599Introduction
2、The Purpose of the tutorial is to model cavitation in a centrifugal pump,which involves the use of a rotation domain and the cavitation model.The problem consists of a five blade centrifugal pump operating at 2160 rpm.The working fluid is water and flow is assumed to be steady and incompressible.Due
3、 to rotational periodicity a single blade passage will be modeled.The initial flow-field will be solved without cavitation.It will be turned on later.ANSYS,Inc.Proprietary 2009 ANSYS,Inc.All rights reserved.Workshop SupplementWS5:Cavitating Centrifugal PumpWS5-3April 28,2009Inventory#002599Start Wor
4、kbench and save the project as centrifugalpump.wbpjDrag CFX into the Project Schematic from the Component Systems toolboxStart CFX-Pre by double clicking SetupWhen CFX-Pre opens,import the mesh by right-clicking on Mesh and selecting Import Mesh ICEM CFDBrowse to pump.cfx5Keep Mesh units in mClick O
5、penWorkbench ANSYS,Inc.Proprietary 2009 ANSYS,Inc.All rights reserved.Workshop SupplementWS5:Cavitating Centrifugal PumpWS5-4April 28,2009Inventory#002599Modifying the material properties:Expand Materials in the Outline treeDouble-click Water On the Material Properties tab change Density to 1000 kg/
6、m3 Change Dynamic Viscosity to 0.001 kg m-1 s-1 under Transport Properties1.Click OKCreating Working FluidsANSYS,Inc.Proprietary 2009 ANSYS,Inc.All rights reserved.Workshop SupplementWS5:Cavitating Centrifugal PumpWS5-5April 28,2009Inventory#002599Setting up the Fluid DomainDouble-click on Default D
7、omainUnder Fluid and Particle Definitions,delete Fluid 1 and then create a new Fluid named Water LiquidSet Material to WaterCreate another new Fluid named Water VapourNext to the Material drop-down list,click the“”icon,then the Import Library Data icon(on the right of the form),and select Water Vapo
8、ur at 25 C under the Water Data objectClick OKBack in the Material panel,select Water Vapour at 25 CClick OKANSYS,Inc.Proprietary 2009 ANSYS,Inc.All rights reserved.Workshop SupplementWS5:Cavitating Centrifugal PumpWS5-6April 28,2009Inventory#002599Setting up the Fluid DomainSet the Reference Pressu
9、re to 0 PaSet Domain Motion to RotatingSet Angular Velocity to 2160 rev min-1Switch on Alternate Rotation ModelMake sure Rotation Axis under Axis Definition is set to Global ZSwitch to the Fluid Models tab,and set the following:Turn on Homogeneous Model in the Multiphase sectionUnder Heat Transfer s
10、et the Option to Isothermal,with a Temperature of 25 CSet Turbulence Option to Shear Stress TransportClick OKANSYS,Inc.Proprietary 2009 ANSYS,Inc.All rights reserved.Workshop SupplementWS5:Cavitating Centrifugal PumpWS5-7April 28,2009Inventory#002599Inlet Boundary ConditionInsert a boundary conditio
11、n named InletOn the Basic Settings tab,set Boundary Type to InletSet Location to INLETSet Frame Type to StationarySwitch to the Boundary Details tabSpecify Mass and Momentum with a Normal Speed of 7.0455 m/sSwitch to the Fluid Values tabFor Water Liquid,set the Volume Fraction to a Value of 1For Wat
12、er Vapour,set the Volume Fraction to a Value of 0Click OKANSYS,Inc.Proprietary 2009 ANSYS,Inc.All rights reserved.Workshop SupplementWS5:Cavitating Centrifugal PumpWS5-8April 28,2009Inventory#002599Outlet Boundary ConditionInset a boundary condition named OutletOn the Basic Settings tab,set Boundary
13、 Type to OpeningSet Location to OUTSet Frame Type to StationarySwitch to the Boundary Details tabSpecify Mass and Momentum using Entrainment,and enter a Relative Pressure of 600,000 PaEnable the Pressure Option and set it to Opening PressureSet Turbulence Option to Zero GradientSwitch to the Fluid V
14、alues tabFor Water Liquid,set the Volume Fraction to a Value of 1For Water Vapour,set the Volume Fraction to a Value of 0Click OKANSYS,Inc.Proprietary 2009 ANSYS,Inc.All rights reserved.Workshop SupplementWS5:Cavitating Centrifugal PumpWS5-9April 28,2009Inventory#002599Periodic InterfaceClick to cre
15、ate an Interface,and name it PeriodicSet the Interface Type to Fluid FluidFor Interface Side 1,set the Region List to DOMAIN INTERFACE 1 SIDE 1 and DOMAIN INTERFACE 2 SIDE 1(use the“”icon and the Ctrl key)For Interface Side 2,set the Region List to DOMAIN INTERFACE 1 SIDE 2 and DOMAIN INTERFACE 2 SI
16、DE 2Set the Interface Models option to Rotational PeriodicityUnder Axis Definition,select Global ZSet Mesh Connection Option to 1:1Click OKANSYS,Inc.Proprietary 2009 ANSYS,Inc.All rights reserved.Workshop SupplementWS5:Cavitating Centrifugal PumpWS5-10April 28,2009Inventory#002599Wall Boundary Condi
17、tionsInsert a boundary condition named StationarySet it to be a Wall,using the STATIONARY locationOn the Boundary Details tab,enable a Wall Velocity and set it to Counter Rotating WallClick OKIn the Outline Tree,right-click on the Default Domain Default boundary and rename it to MovingThe default be
18、havior for the Moving boundary condition is to move with the rotating domain,so there is nothing that needs to be setANSYS,Inc.Proprietary 2009 ANSYS,Inc.All rights reserved.Workshop SupplementWS5:Cavitating Centrifugal PumpWS5-11April 28,2009Inventory#002599InitializationClick to initialize the sol
19、utionOn the Fluid Settings form,set Water Liquid Volume Fraction to Automatic with Value,and set the Volume Fraction to 1Set Water Vapour Volume Fraction to Automatic with Value,and set the Volume Fraction to 0Click OKANSYS,Inc.Proprietary 2009 ANSYS,Inc.All rights reserved.Workshop SupplementWS5:Ca
20、vitating Centrifugal PumpWS5-12April 28,2009Inventory#002599Solver ControlDouble click Solver Control in the Outline treeSet Timescale Control to Physical timescaleA commonly used timescale in turbomachinery is 1/omega,where omega is the rotation rate in radians per second.You can use an expression
21、to determine a timestep from this.In this case,2/omega will be used to achieve faster convergence.Enter the following expression in the Physical Timescale box:1/(pi*2160 min-1)Set Residual Target to 1e-5On the Advanced Options tab,turn on Multiphase Control,then turn on Volume Fraction Coupling and
22、set the Option to CoupledClick OKANSYS,Inc.Proprietary 2009 ANSYS,Inc.All rights reserved.Workshop SupplementWS5:Cavitating Centrifugal PumpWS5-13April 28,2009Inventory#002599Output ControlDouble Click on Output Control in the Outline treeOn the Monitor tab,turn on Monitor OptionsUnder Monitor Point
23、s and Expressions,create a new object and call it InletPTotalAbsSet Option to ExpressionSpecify the following expression:massFlowAve(Total Pressure in Stn Frame)InletCreate a new object called InletPStatic,and set Option to Expression Specify the following expression:areaAve(Pressure)InletClick OKAN
24、SYS,Inc.Proprietary 2009 ANSYS,Inc.All rights reserved.Workshop SupplementWS5:Cavitating Centrifugal PumpWS5-14April 28,2009Inventory#002599SolverClose CFX-Pre and switch to the Workbench Project windowSave the projectNow double click on Solution in the Project Schematic to start the Solver ManagerW
25、hen the Solver Manager opens,click Start RunWhen the solution has completed,close the Solver Manager and return to the Project windowSave the projectANSYS,Inc.Proprietary 2009 ANSYS,Inc.All rights reserved.Workshop SupplementWS5:Cavitating Centrifugal PumpWS5-15April 28,2009Inventory#002599Post-proc
26、essingView the results in CFD-Post by double clicking Results in the Project SchematicInsert a Contour by clickingFor the Location,click ,expand Regions and then select BLADESet Variable to Absolute Pressure from the extended listSet Range to GlobalOn the Render tab switch off Lighting and Show cont
27、our LinesClick ApplyANSYS,Inc.Proprietary 2009 ANSYS,Inc.All rights reserved.Workshop SupplementWS5:Cavitating Centrifugal PumpWS5-16April 28,2009Inventory#002599Post-processingInsert another Contour on the HUB location,using the variable Absolute Pressure coloured by Local Range.Turn off Lighting a
28、nd Show Contour Lines.Insert another Contour on the SHROUD location,using the variable Absolute Pressure coloured by Local Range.Turn off Lighting and Show Contour Lines.The minimum pressure is above the Saturation Pressure of 2650 Pa for Water here.In the next step,the outlet pressure will be reduc
29、ed enough to initiate Cavitation.ANSYS,Inc.Proprietary 2009 ANSYS,Inc.All rights reserved.Workshop SupplementWS5:Cavitating Centrifugal PumpWS5-17April 28,2009Inventory#002599Adding another AnalysisClose CFD-Post and return to the Project SchematicClick the arrow next to the A cell and select Duplic
30、ateA new CFX project is created as a copy of the firstChange the name of the new Simulation to CavitationUse the arrow next to the A cell to Rename it to No CavitationSave the ProjectDouble-click Setup for the Cavitation simulation to open CFX-PreANSYS,Inc.Proprietary 2009 ANSYS,Inc.All rights reser
31、ved.Workshop SupplementWS5:Cavitating Centrifugal PumpWS5-18April 28,2009Inventory#002599Physics ModificationsEdit the Default DomainOn the Fluid Pair Models tab set Mass Transfer to Cavitation Set Option to Rayleigh PlessetTurn on Saturation PressureSet a Saturation Pressure of 2650 PaClick OKEdit
32、the Outlet Boundary ConditionOn the Boundary Details tab,set the Relative Pressure to 300,000 PaClick OKMost cavitation solutions should be performed by turning cavitation on and then successively lowering the system pressure over several runs to more gradually induce cavitation.To speed up this wor
33、kshop,a sudden change in pressure is introduced.Note that this approach may not be suitable for modelling some industrial cases.ANSYS,Inc.Proprietary 2009 ANSYS,Inc.All rights reserved.Workshop SupplementWS5:Cavitating Centrifugal PumpWS5-19April 28,2009Inventory#002599Physics ModificationsEdit Solv
34、er ControlSet the Max.Iterations to 150Set the Residual Target to 1e-4Click OKClose CFX-Pre and save the projectIn the Project Schematic,drag cell A3 onto cell B3The non-cavitating solution will be used as the initial guess for the cavitating solutionDouble-click Solution for the Cavitation systemIn
35、 the Solver Manager note that the initial conditions have been provided from the project schematicClick Start RunANSYS,Inc.Proprietary 2009 ANSYS,Inc.All rights reserved.Workshop SupplementWS5:Cavitating Centrifugal PumpWS5-20April 28,2009Inventory#002599Cavitation SolutionThere is a significant spi
36、ke in residuals,in part due to the outlet pressure difference,but also due to the fact that the absolute pressure is low enough to induce cavitation.When the run completes,close the Solver Manager and return to the Project SchematicSave the project1.Double-click Results for the Cavitation project to
37、 openCFD-PostANSYS,Inc.Proprietary 2009 ANSYS,Inc.All rights reserved.Workshop SupplementWS5:Cavitating Centrifugal PumpWS5-21April 28,2009Inventory#002599Post-processingIf it is not enabled,turn on visibility for the Wireframe and turn off visibility for any User Locations and PlotsCreate an XY Pla
38、ne at Z=0.01 mColour it by Absolute Pressure(the variable is available in the Extended List by clicking ).Use a Global RangeThe minimum absolute pressure is equivalent to the Saturation Pressure specified earlier,which is a strong hint that some cavitation has occurredChange the Colour Variable to W
39、ater Vapour.Volume FractionChange the Colour Map to Blue to WhiteANSYS,Inc.Proprietary 2009 ANSYS,Inc.All rights reserved.Workshop SupplementWS5:Cavitating Centrifugal PumpWS5-22April 28,2009Inventory#002599Post-processingTurn off visibility for Plane 1Create a Volume using the Isovolume methodSet t
40、he Variable to Water Vapour.Volume FractionSet Mode to Above Value,and enter a value of 0.5To view 360 degrees of the model,double-click Default TransformUncheck Instancing Info from DomainSet#of copies to 5Set#of Passages to 5Click OKANSYS,Inc.Proprietary 2009 ANSYS,Inc.All rights reserved.Workshop
41、 SupplementWS5:Cavitating Centrifugal PumpWS5-23April 28,2009Inventory#002599Post-processingThe main area of cavitation exists between the suction side of the blade and the shroud in this geometry.A secondary area of cavitation is just behind the leading edge of the blade on the pressure sideFurther
42、 steps to try:Calculate torque on the BLADE using the function calculator(hint,use the extended region list to find the BLADE,and use Global Z axis)Plot velocity Vectors on Plane 1,using the variableWater Liquid.Velocity in Stn.FrameCalculate the mass flow through the pump(hint:use the function calculator to evaluate massFlow at the Outlet region)Using a similar method to step 2,calculate the drop in Total Pressure from Inlet to OutletPlot Streamlines,starting from the Inlet location
