汽轮机fluent模拟算例

ing Sliding MeshesIntroductionThe analysis of turbomachinery often involves the examination of the unsteady effects due toflow interaction between the stationary components and the rotating blades.In this tutorial,the sliding mesh capability of FLUENT is used to to analyze the unsteady flow in an axial compressor stage.The rotor-stator interaction is modeled by allowing the mesh associated with the rotor blade row to rotate relative to the stationary mesh associated with the stator blade row.This tutorial demonstrates how to do the following:•Create periodic zones.•Set up the unsteady solver and boundary conditions for a sliding mesh simulation.•Set up the grid interfaces for a periodic sliding mesh model.•Sample the time-dependent data and view the mean value.PrerequisitesThis tutorial assumes that you are familiar with the menu structure in FLUENT and that you have completed Tutorial1.Some steps in the setup and solution procedure will not be shown explicitly.Problem DescriptionThe model represents a single-stage axial compressor comprised of two blade rows.The first row is the rotor with16blades,which is operating at a rotational speed of37,500 rpm.The second row is the stator with32blades.The blade counts are such that the domain is rotationally periodic,with a periodic angle of22.5degrees.This allows you to model only a portion of the geometry,namely,one rotor blade and two stator blades.Due to the high Reynolds number of theflow and the relative coarseness of the mesh (both blade rows are comprised of only13,856cells total),the analysis will employ the inviscid model,so that FLUENT is solving the Euler equations.Using Sliding MeshesoutletFigure11.1:Rotor-Stator Problem DescriptionUsing Sliding MeshesSetup and SolutionPreparation1.Download sliding_mesh.zip from the Fluent er Services Center or copyit from the FLUENT documentation CD to your working folder(as described inTutorial1).2.Unzip sliding_mesh.zip.axial comp.msh can be found in the sliding mesh folder created after unzippingthefile.3.Start the3D(3d)version of FLUENT.Step1:Grid1.Read in the meshfile axial comp.msh.File−→Read−→Case...2.Check the grid.Grid−→CheckFLUENT will perform various checks on the mesh and will report the progress inthe console.Pay particular attention to the minimum volume,and make sure thisis a positive number.Warnings will be displayed regarding unassigned interface zones,resulting in thefailure of the grid check.You do not need to take any action at this point,as thisissue will be rectified when you define the grid interfaces in a later step.Using Sliding Meshes3.Define the units for the grid.Define−→Units...(a)Select angular-velocity in the Quantities selection list.(b)Select rpm in the Units selection list.(c)Select pressure in the Quantities selection list.(d)Select atm in the Units selection list.(e)Close the Set Units panel.4.Display the grid(Figure11.2).Display−→Grid...Using Sliding Meshes(a)Retain the default selections in the Surfaces selection list.(b)Click Display and close the Grid Display panel.(c)Rotate the view to get the display shown in Figure11.2.Figure11.2:Rotor-Stator Outline DisplayThe inlet to the rotor mesh is colored blue,the interface between the rotor and stator meshes is colored yellow,and the outlet of the stator mesh is colored red.e the text user interface to change zones rotor-per-1and rotor-per-3fromwall zones to periodic zones.(a)Press<Enter>in the console to get the command prompt(>).(b)Type the commands shown in boxes as follows:Using Sliding Meshes>grid/grid>modify-zones/grid/modify-zones>list-zonesid name type material kind -----------------------------------------------------------------------13fluid-rotor fluid air cell 28fluid-stator fluid air cell 2default-interior:0interior face 15default-interior interior face 3rotor-hub wall aluminum face 4rotor-shroud wall aluminum face 7rotor-blade-1wall aluminum face 8rotor-blade-2wall aluminum face 16stator-hub wall aluminum face 17stator-shroud wall aluminum face 20stator-blade-1wall aluminum face 21stator-blade-2wall aluminum face 22stator-blade-3wall aluminum face 23stator-blade-4wall aluminum face 5rotor-inlet pressure-inlet face 19stator-outlet pressure-outlet face 10rotor-per-1wall aluminum face 12rotor-per-2wall aluminum face 24stator-per-2wall aluminum face 26stator-per-1wall aluminum face 6rotor-interface interface face 18stator-interface interface face 11rotor-per-4wall aluminum face 9rotor-per-3wall aluminum face 25stator-per-4wall aluminum face 27stator-per-3wall aluminum face /grid/modify-zones>make-periodicPeriodic zone[()]10Shadow zone[()]9Rotational periodic?(if no,translational)[yes]yesCreate periodic zones?[yes]yesall176faces matched for zones10and9.zone9deletedcreated periodic zones.Using Sliding Meshes6.Similarly,change the following wall zone pairs to periodic zones:Zone Pairs Respective Zone IDsrotor-per-2and rotor-per-412and11stator-per-1and stator-per-326and27stator-per-2and stator-per-424and25Step2:Models1.Define the solver settings.Define−→Models−→Solver...(a)Select Density Based from the Solver group box.(b)Retain the selection of Green-Gauss Cell Based from the Gradient Option groupbox.(c)Retain the selection of Implicit from the Formulation list.(d)Select Unsteady from the Time list.(e)Select2nd-Order Implicit from the Unsteady Formulation list.(f)Click OK to close the Solver panel.Using Sliding Meshes2.Enable the inviscid model.Define−→Models−→Viscous...(a)Enable Inviscid.(b)Click OK.Using Sliding MeshesStep3:Materials1.Specify air(the default material)as thefluid material,using the ideal gas law tocompute density.Define−→Materials...(a)Retain the default entry of air in the Name text entryfield.(b)Select ideal-gas from the Density drop-down list in the Properties group box.(c)Retain the default values for all other properties.(d)Click Change/Create and close the Materials panel.Using Sliding MeshesStep4:Operating Conditions1.Set the operating pressure.Define−→Operating Conditions...(a)Enter0atm for the Operating Pressure.(b)Click OK to close the Operating Conditions panel.Since you have set the operating pressure to zero,you will specify the boundarycondition inputs for pressure in terms of absolute pressures when you define themin a later step.Boundary condition inputs for pressure should always be relative tothe value used for operating pressure.Step5:Boundary ConditionsDefine−→Boundary Conditions...1.Set the boundary conditions for thefluid in the rotor(fluid-rotor).(a)Make sure that(0,0,1)is entered for X,Y,and Z under Rotation-Axis Direction.(b)Select Moving Reference Frame from the Motion Type drop-down list.(c)Enter37500rpm for Speed in the Rotational Velocity group box.Scroll down tofind the Speed number-entry box.(d)Click OK to close the Fluid panel.2.Set the boundary conditions for thefluid in the stator(fluid-stator).(a)Make sure that(0,0,1)is entered for X,Y,and Z under Rotation-Axis Direction.(b)Make sure that Stationary is selected from the Motion Type drop-down list.(c)Click OK to close the Fluid panel.3.Set the boundary conditions for the inlet(rotor-inlet).(a)Enter1.0atm for the Gauge Total Pressure.(b)Enter0.9atm for the Supersonic/Initial Gauge Pressure.(c)Click the Thermal tab and enter288K for Total Temperature.(d)Click OK to close the Pressure Inlet panel.4.Set the boundary conditions for the outlet(stator-outlet).(a)Enter1.08atm for the Gauge Pressure.(b)Enable the Radial Equilibrium Pressure Distribution option.(c)Click the Thermal tab and enter288K for Backflow Total Temperature.(d)Click OK to close the Pressure Outlet panel.Note:The momentum settings and temperature you input at the pressure outlet will be used only ifflow enters the domain through this boundary.It is impor-tant to set reasonable values for these downstream scalar values,in caseflow reversal occurs at some point during the calculation.5.Retain the default boundary conditions for all wall zones.Note:For wall zones,FLUENT always imposes zero velocity for the normal velocity component,which is required whether or not thefluid zone is moving.This condition is all that is required for an inviscidflow,as the tangential velocity is computed as part of the solution.6.Close the Boundary Conditions panel.Step6:Grid Interfaces1.Create a periodic grid interface between the rotor and stator mesh regions.Define−→Grid Interfaces...(a)Enter int for Grid Interface.(b)Enable Periodic in the Interface Type group box.Enabling this option,allows FLUENT to treat the interface between the slidingand non-sliding zones as periodic where the two zones do not overlap.(c)Select rotor-interface in the Interface Zone1list.Note:In general,when one interface zone is smaller than the other,it is recommended that you choose the smaller zone as Interface Zone1.Inthis case,since both zones are approximately the same size,the order isnot significant.(d)Select stator-interface in the Interface Zone2list.(e)Click Create and close the Grid Interfaces panel.2.Check the grid again to verify that the warnings displayed earlier have been re-solved.Grid−→CheckStep7:Solution1.Set the solution parameters.Solve−→Controls−→Solution...(a)Make sure that Second Order Upwind is selected from the Flow drop-down listin the Discretization group box.(b)Click OK to close the Solution Controls panel.2.Enable the plotting of residuals during the calculation.Solve−→Monitors−→Residual...(a)Enable Plot in the Options group box.(b)Select relative from the Convergence Criterion drop-down list.(c)Enter0.01in thefields under Relative Criteria for every Residual(continuity,x-velocity,y-velocity,z-velocity,and energy).(d)Click OK to close the Residual Monitors panel.3.Enable the plotting of the data at the inlet(rotor-inlet),outlet(stator-outlet),andthe interface(stator-interface).Solve−→Monitors−→Surface...(a)Set the Surface Monitors to3.(b)Enable Plot,Print,and Write for each monitor(monitor-1,monitor-2,andmonitor-3).(c)Select Time Step from the When drop-down list for each monitor(monitor-1,monitor-2,and monitor-3).(d)Click the Define...button for monitor-1to open the Define Surface Monitorpanel.i.Select Mass Flow Rate from the Report Type drop-down list.ii.Select Flow Time from the X Axis drop-down list.iii.Select rotor-inlet from the Surfaces selection list.iv.Click OK to close the Define Surface Monitor panel.(e)Define monitor-2to report the massflow rate at the outlet(stator-outlet)asshown in the following panel:!Be sure to deselect rotor-inlet from the Surfaces selection list,before scrolling down to select stator-outlet.(f)Define monitor-3to report the area-weighted average of the static pressure atthe interface(stator-interface)as shown in the following panel:!Be sure to deselect stator-outlet from the Surfaces selection list before scrolling down to select stator-interface.(g)Click OK to close the Surface Monitors panel.4.Initialize the solution using the values at the inlet(rotor-inlet).Solve−→Initialize−→Initialize...(a)Select rotor-inlet from the Compute From drop-down list.(b)Select Absolute from the Reference Frame list.(c)Click Init and close the Solution Initialization panel.5.Save the initial casefile(axial comp.cas).File−→Write−→Case...6.Run the calculation for one revolution of the rotor.Solve−→Iterate...(a)Enter6.6666e-6s for the Time Step Size.This time step represents the length of time during which the rotor will rotate1.5degrees.Since the periodic angle of the rotor is22.5degrees,the passingperiod of the rotor blade will equal15time steps,and a complete revolution of the rotor will take240time steps.(b)Enter240for the Number of Time Steps.(c)Retain the default setting of20for the Max Iterations per Time Step in theIteration group box.(d)Click Iterate.The solution will converge in approximately3900iterations.The residuals jump at the beginning of each time step and then fall at least two to three orders of magnitude.Also,the relative convergence criteria is achieved before reaching the maximum iteration limit(20)for each time step,indicating the limit does not need to be increased.7.Examine the monitor histories for thefirst revolution of the rotor(Figures11.4,11.5,and11.6).Figure11.3:Residual History for the First Revolution ofthe RotorRevolutionFigure11.5:Mass Flow Rate at the Outlet During the FirstThe monitor histories show that large variations inflow rate and interface pressure occur early in the calculation,which are greatly reduced as time-periodicity is approached.8.Save the case and datafiles(axial comp-0240.cas and axial comp-0240.dat).File−→Write−→Case&Data...!When the sliding mesh model is used,you must save a casefile whenever a datafile is saved.This is because the casefile contains the grid information,which is changing with time.Note:For unsteady-state calculations,you can add the character string%t to the file name so that the iteration number is automatically appended to the name(e.g.,by entering axial comp-%t for the File Name in the Select File dia-log box,FLUENT will savefiles with the names axial comp-0240.cas and axial comp-0240.dat).9.Rename the monitorfile names in preparation for further iterations.By saving the monitor histories under a newfile name,the range of the axes will automatically be set to show only the data generated during the next set of iterations.This will scale the plots so that thefluctuations are more visible.Solve−→Monitors−→Surface...(a)Click the Define...button for monitor-1to open the Define Surface Monitorpanel.i.Enter monitor-1b.out for the File Name.ii.Click OK to close the Define Surface Monitor panel.(b)Similarly,change the File Name for monitor-2and monitor-3to be monitor-2b.outand monitor-3b.out respectively.(c)Click OK to close the Surface Monitors panel.Extra:Instead of creating a newfile for each monitor,you could have adjusted the ranges of the axes to make thefluctuations visible,and then allowed the data from the next set of iterations to be appended onto the original monitor files.To do this,click the Axes...button in the Define Surface Monitor panel of each monitor,disable the Auto Range option,enter in appropriate values in the Range group box,and click Apply.10.Continue the calculation for720more time steps to simulate three more revolutionsof the rotor.Solve−→Iterate...!Calculating three more revolutions will require significant CPU re-sources.Instead of calculating the solution,you can read the datafile(axial comp-0960.dat)with the precalculated solution.This datafilecan be found in the folder where you found the meshfile.The calculation will run for approximately14,350more iterations.11.Examine the monitor histories for the next three revolutions of the rotor to verifythat the solution is time-periodic(Figures11.7,11.8,and11.9).Note:If you read the provided datafile instead of iterating the solution for three revolutions,the monitor histories can be displayed by using the Plot/File...menu option.Simply click the Add button in the File XY Plot panel,select oneof the monitor histories in the Select File dialog box,click OK,and then clickPlot.Figure11.7:Mass Flow Rate at the Inlet During the Next3RevolutionsFigure11.9:Static Pressure at the Interface During the Next3RevolutionsNote that though the axes have been reset to show smaller ranges of values,there are still smallfluctuations in the monitor histories that are not clearly visible.12.Save the case and datafiles(axial comp-0960.cas and axial comp-0960.dat).File−→Write−→Case&Data...13.Change the File Name for monitor-1,monitor-2,and monitor-3to be monitor-1c.out,monitor-2c.out,and monitor-3c.out,respectively(as described in a previous step),in preparation for further iterations.Solve−→Monitors−→Surface...14.Continue the calculation for onefinal revolution of the rotor,while saving datasamples for the postprocessing of the time statistics.Solve−→Iterate...(a)Enter240for the Number of Time Steps.(b)Enable Data Sampling for Time Statistics in the Options group box.(c)Click Iterate.(d)Close the Iterate panel.The calculation will run for approximately4800more iterations.15.Save the case and datafiles(axial comp-1200.cas and axial comp-1200.dat).File−→Write−→Case&Data...Step8:PostprocessingIn the next two steps you will examine the time-averaged values for the massflow rates at the inlet and the outlet during thefinal revolution of the rotor.By comparing these values,you will verify the conservation of mass on a time-averaged basis for the system over the course of one revolution.1.Examine the time-averaged massflow rate at the inlet during thefinal revolutionof the rotor(as calculated from monitor-1c.out).Plot−→FFT...(a)Click the Load Input File...button to open the Select File dialog box.i.Select All Files from the Files of type drop-down list.ii.Select monitor-1c.out from the list offiles.iii.Click OK to close the Select File dialog box.Signal panel.i.Examine the values for Min,Max,Mean,and Variance in the Signal Statis-tics group box.ii.Close the Plot/Modify Input Signal panel.(c)Select the folder path ending in monitor-1c.out from the Files selection list.(d)Click the Free File Data button.2.Examine the time-averaged massflow rate at the outlet during thefinal revolutionof the rotor(as calculated from monitor-2c.out),and plot the data.Plot−→FFT...(a)Click the Load Input File...button to open the Select File dialog box.i.Select All Files from the Files of type drop-down list.ii.Select monitor-2c.out from the list offiles.iii.Click OK to close the Select File dialog box.Signal panel.i.Examine the values for Min,Max,Mean,and Variance in the Signal Statis-tics group box.Note that the outlet massflow rate values correspond very closely withthose from the inlet,with the mean having approximately the same ab-solute value but with opposite signs.Thus,you can conclude that massis conserved on a time-averaged basis during thefinal revolution of therotor.ii.Click the Set Defaults button.iii.Click Apply/Plot to display the massflow rate at the outlet(Figure11.10).iv.Close the Plot/Modify Input Signal panel.(c)Close the Fourier Transform panel.Figure11.10:Mass Flow Rate at the Outlet During the Final Revolution3.Display contours of the mean static pressure on the walls of the axial compressor.Display−→Contours...(a)Enable Filled in the Options group box.(b)Select Unsteady Statistics...and Mean Static Pressure from the Contours ofdrop-down lists.(c)Select wall in the Surface Types selection list.Scroll down the Surface Types selection list tofind wall.(d)Click Display and close the Contours panel.(e)Rotate the view to get the display shown in Figure11.11.Figure11.11:Mean Static Pressure on the Outer Shroud of the Axial Compressor Shock waves are clearly visible in theflow near the outlets of the rotor and stator, as seen in the areas of rapid pressure change on the outer shroud of the axial compressor.SummaryThis tutorial has demonstrated the use of the sliding mesh model for analyzing unsteady rotor-stator interaction in an axial compressor stage.The model utilized the density-based solver in conjunction with the unsteady,dual-time stepping algorithm to compute the inviscidflow through the compressor stage.The solution was calculated over time until the monitored variables displayed time-periodicity(which required several revolu-tions of the rotor),after which time-averaged data was collected while running the case for the equivalent of one additional rotor revolution(240time steps).The Fast Fourier Transform(FFT)utility in FLUENT was employed to determine the time averages from stored monitor data.Although not described in this tutorial,you can further use the FFT utility to examine the frequency content of the unsteady monitor data(in this case, you would observe peaks corresponding to the passing frequency and higher harmonics of the passing frequency).Further ImprovementsThis tutorial guides you through the steps to reach a second-order solution.You may be able to obtain a more accurate solution by adapting the grid.Adapting the grid can also ensure that your solution is independent of the grid.These steps are demonstrated in Tutorial1.。