Tutorial Meshing Of A Simple Centrifugal Pump With Ansys -Books Pdf

Tutorial Meshing of a simple centrifugal pump with ANSYS
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1 Introduction 1,1 Introduction, This document is a tutorial that describes procedure of creation of structured and unstructured. computational meshes for a simple centrifugal pump Meshing is done with ANSYS ICEM. 16 2 Such meshes can then be used for CFD Computational Fluid Dynamics simulation. The geometry of the pump is based on the description in 1 and is provided in three stp. The meshes created with this tutorial are rather coarse for two reasons The main goal was. to decribe the process itself Secondly depending upon the ANSYS license the user might. be limited to run only CFD cases with up to 512 000 cells elements Of course the user can. choose to make finer meshes which would result in improved accuracy of CFD simulations. The authors of this tutorial are not related to ANSYS company in any way. 2 Case description, Centrifugal pumps are widely used in engineering applications Therefore the current docu. ment instructs to create computational grids meshes for a given geometry and to prepare a. setup for the CFD simulation, The presented case is a very simple shrouded centrifugal pump impeller Fig 1 the. scaled Grundfos CR4 with medium specific speed The PhD thesis by Pedersen 1 in. cludes experimental and CFD results for the pump The experiments were performed for a. transparent impeller produced in perspex by Particle Image Velocimetry PIV Fig 2 and. Laser Doppler Velocimetry LDV techniques The CFD analysis was performed with Large. Eddy Simulation LES,3 Geometry, The provided impeller geometry is an approximation of the geometrical data Table 1 pro. vided in 1,Basic data of the impeller,Inlet diameter D1 77 mm.
Outlet diameter D2 190 mm,Inlet height b1 13 8 mm,Outlet height b2 5 8 mm. Number of blades Z1 6,Blade thickness ti 3 mm,Inlet blade angle 1 19 7. Outlet blade angle 2 18 4,Table 1 Impeller characteristics 1. A S kerlavaj E Nobile January 2018,2 3 Geometry,Figure 1 Geometry of the pump impeller 1. Figure 2 Details of the PIV setup 1,A S kerlavaj E Nobile January 2018.
4 Computational grids ANSYS ICEM 3, Usually the CFD computational domain is not limited only to the blade section as pre. sented in Fig 1 but includes also an inlet and an outlet part domain The inlet extension. provides more realistic inlet conditions whereas the outlet one provides more realistic condi. tions velocity vectors at the outlet from the impeller. Therefore three geometry files are provided corresponding to three computational do. mains of CFD simulations inlet impeller and outlet domain In Table 2 the relation of. filenames and computational domains is provided The whole geometry is provided for a 60. section 1 Z1 of the full circle,Filename Part No in Fig 3 Computational domain. geometry inlet3 stp 1 inlet,geometry impeller3 agdb 2 impeller. geometry outlet3 stp 3 outlet, Table 2 Geometry filenames and computational domains. Figure 3 Geometry specified by three geometry files. 4 Computational grids ANSYS ICEM, This section describes how to create computational grids for all three parts provided by three.
geometry files in ANSYS ICEM It is suggested to put each geometry file in a separate file. A S kerlavaj E Nobile January 2018,4 4 1 Computational grid 1. 4 1 Computational grid 1, Start ANSYS ICEM by clicking All programs ANSYS 16 2 Meshing ICEM CFD 16 2. Set the working directory of the first file geometry inlet stp File Change Working Dir. Open the geometry file of part 1 Click File Import Geometry Legacy STEP IGES. select a file click Open then click Apply in the window presented in Fig 4. Figure 4 Importing the geometry file, The geometry is imported Save the project to select project s name File Save Project. As write mesh inlet prj and click Save, In the window that represents geometry the left mouse button LMB rotates the geometry. the central mouse button CMB moves geometry and the right mouse button RMB scales. up down the geometry In the left region of the screen a Display Tree Fig 5 is shown which. can be used for control of display in the main window It is possible to click on the sign to. expand the tree,Figure 5 Display Tree, The imported part represents an inlet part above the impeller in Fig 2 From the figure it.
can be concluded that side walls of the inlet geometry do not rotate. The first step is to set the correct units and size Click LMB Settings Model Units. Set the units to Milimeters and click OK The geometry size should be increased by 1000. times In the Main Toolbar click Geometry Transform Geometry Use the settings. according to Fig 6 and click Enable selection of points curves surfaces and bodies in the. A S kerlavaj E Nobile January 2018,4 1 Computational grid 1 5. floating menu choices in the menu should be enabled Then press a on. the keyboard shortcut for select all and click Apply Click Fit Window icon to fit the. geometry in the screen window,Figure 6 Scaling the geometry by a factor of 1000. The next step is the creation of the parts in the Display Tree which can later represent. selectable surface parts of the meshes in e g ANSYS CFX Pre CFX Pre or similar software. is used to set up the CFD simulation by prescribing boundary conditions initial conditions. numerical models etc Another advantage of creating parts is grouping surfaces with equal. size of mesh elements in case of unstructured grids. Five parts will be created in the Display Tree of the mesh inlet prj project geom1 in. geom1 out geom1 walls geom1 per1 and geom1 per2 the geom1 label was used to repre. sent the inlet part domain of the whole case, Rotate the geometry so that Zaxis is pointing upward turn on surfaces in the Display Tree. and click on solid simple display icon in the Main Menu The result is presented in Fig 7. To create a part containing a surface the following procedure can be used. Right click on Parts then left click on Create Part. Enter write the part s name in the top field, Click on icon next to Create Part by Selection The most important functionality of. the pop up window is to toggle on off selection of points curves surfaces and bodies. by clicking the four icons Turn on only the selection of surfaces. A S kerlavaj E Nobile January 2018,6 4 1 Computational grid 1.
Figure 7 The geometry of the first domain inlet domain before creation of parts. Pick up the desired surface s by left clicking LC on surface s then finish with a. middle button click MC Before finishing it is possible to undo the picking up actions. in a reverse direction by using a right mouse button RC During the pick up process. it is possible to rotate move the geometry by pressing F9 button and re pressing to. re enter the pick up process,MC again to finish the selection process. A new part appears in the Display Tree and the part s surface s change its their colour. By using the described procedure create the five parts The part geom1 in includes the. inlet surface with the highest Z value the surface at the top in Fig 7 The part geom1 out. includes the outlet surface with the lowest Z value The part geom1 walls includes the. annular section surface There should be two periodic parts Suppose that index Per1 of the. periodic parts is on the left side of index 3 in Fig 3 for geometry 3 whereas index Per2 is. on the right side of index 3 Therefore the part geom1 per1 is the visible vertical surface in. Fig 7 whereas the part geom1 per2 is the hidden vertical surface in Fig 7. In the Main Toolbar click Geometry Create Body, Turn on points visibility and turn off visibility of surfaces in the Display Tree Create a. body part named BODY INLET by using Centroid of two points and picking up two points. e g as in Fig 8 MC twice Check that the centroid body point lies within the geometry. bounded by surfaces rotate the geometry to check it. In the Main Toolbar click Mesh Global Mesh Setup Set the global mesh parame. ters according to Fig 9 Max element size 4 0 Prism initial height 0 1 ratio 1 2 layers 10. Rotational period axis 0 0 1 angle 60 Click Apply in each of the three windows It. should be noted that in some cases complex ones the creation of prism layers mail fail with. the latter setting In such cases it is better to set only two parameters for prism elements thus. leaving the total prism height floating For instance set only the ratio with e g 7 layers. and later subdivide and rearrange the layers as it will be done for the blade mesh. A S kerlavaj E Nobile January 2018,4 1 Computational grid 1 7. Figure 8 Create Body selection of two points,Figure 9 Global mesh setup. A S kerlavaj E Nobile January 2018,8 4 1 Computational grid 1.
Besides setting the global parameters it is possible to set local parameters for specific. parts In the Main Toolbar click Mesh Part Mesh Setup A pop up window appears. Choose parameters accurding to Fig 10 BODY INLET part will have a hexa core mesh. max size 4 prism layers will be located at part GEOM1 WALLS Instead of putting 4 to. the max size it would be possible to leave the setting as 0 because of the previously defined. global parameters Prism elements are needed only at walls The hexa core mesh converts. tetrahedral elements to haxagonal elements thus reducing number of elements decreased. elements vs nodes ratio To finish press Apply then Dismiss. Figure 10 Part mesh setup, After defining the mesh parameters it is time to create the mesh In the Main Toolbar. click Mesh Compute Mesh In the Compute Mesh window turn on creation of prism. layers and mesh hexa core after the tetra meshing Fig 11 It would be also possible to create. prism layers and hexa core in a separate meshing process This can be useful for complicated. geometries where it is better to create a high quality tetra mesh first quality above 0 2 or. 0 3 Press Compute,Figure 11 Compute Mesh window, To view the mesh if it is not visible turn on Shells in Mesh tree of the Display Tree as. A S kerlavaj E Nobile January 2018,4 2 Computational grid 2 9. well as surface parts left click in the Main Toolbar then click Fit Window icon in the. Main Toolbar The mesh is presented in Fig 12,Figure 12 Mesh inlet part. Check the mesh for errors Click Edit Mesh Check Mesh Click Apply A pop. up window appears Select the two periodic parts and click Accept Confirm the deletion of. unconnected vertices click Yes, Check the quality of the mesh Click Edit Mesh Display Mesh Quality The mesh.
quality is just above 0 2, Improve the mesh quality Click Edit Mesh Smooth Mesh Globally Set the. smoothing parameters according to Fig 13 Click Apply The new quality is above 0 25 If it. was smaller the smoothing would be repeated with quality limit set to 0 2 and all previously. Frozen types of meshes set to Smooth,Repeat the previously described Check Mesh step. Click File Save Project, If the user is using ANSYS CFX for CFD simulations the mesh has to be exported to a. cfx5 file format Click Output Select solver and set the field Output solver to ANSYS. CFX Click Apply Then click Output Write input Confirm saving the project Click. Done in another pop up window Wait until you see Done with translation message in the. Message window The mesh is exported Now close the project you can as well save it. 4 2 Computational grid 2, Start ANSYS ICEM by clicking All programs ANSYS 16 2 Meshing ICEM CFD 16 2. Set the working directory of the second geometry file geometry impeller3 agdb File. A S kerlavaj E Nobile January 2018,10 4 2 Computational grid 2.
Figure 13 Smoothing the mesh,Change Working Dir, Open geometry file geometry impeller3 agdb Click File Import Model select a file. click Open in the menu set units to Milimeter and then click Apply. Save the project to select project s name File Save Project As write mesh impeller prj. and click Save, Click Settings Model Units in the Main Menu Set Topo Tolerance to 0 0008 and. Triangulation Tolerance to 0 00001 then click OK, Create the following surface parts remember the Surfaces in the Display Tree should be. enabled for the selection of the surfaces,geom2 blade LE. geom2 blade PS,geom2 blade SS,geom2 blade TE,geom2 shroud.
geom2 nowalls top,geom2 nowalls bottom,A S kerlavaj E Nobile January 2018. 4 2 Computational grid 2 11,geom2 per1,geom2 per2, The surface parts are presented in Fig 14 and Fig 15 The inlet surface is the one at the largest. value of Z The index LE stands for leading edge of the blade small surface TE stands for. trailing edge of the blade small surface the SS is suction side and the PS is pressure side. Hub is the non curved surface at the impeller bottom at the lowest value of Z whereas. shroud are the two curved surfaces opposite to the hub The top and the bottom surfaces at the. largest radius after the TE marked geom2 nowalls do not represent the impeller They are. there just for numerical purposes Create a body with name BODY IMPELLER. Figure 14 Surface parts of the impeller blade,Figure 15 Surface parts of the impeller blade. Delete two curves and six points as presented in Fig 16 Create part POINTS with all. points in the geometry Create part CURVES that should contain all curves in the geometry. Set the global mesh setup in the Main Toolbar click Mesh Global Mesh Setup. Set the global mesh parameters according to Fig 17 Max element size 4 0 Tetra edge crite. rion 0 05 No of prism layers 1 Rotational period axis 0 0 1 angle 60 In addition in. A S kerlavaj E Nobile January 2018,12 4 2 Computational grid 2. Figure 16 Curves and points Blue curves to be deleted Red points to be deleted Green. curves to be set with Curve Mesh Setup, the Global Prism Settings set the Number of surface smoothing steps to 0 The height of the.
channel at the outlet from the impeller is equal to 5 8 mm which is similar to the maximum. size of the mesh element Therefore only one prism layer was created which will be later. subdivided into more layers The tetra edge criterion was decreased to capture the curves of. the trailing edge properly otherwise the trailing edge might become jagged. The next step is setting parameters of the mesh for the parts In the Main Toolbar click. Mesh Part Mesh Setup A pop up window appears Choose parameters accurding to. Fig 18 BODY IMPELLER part will have a hexa core mesh max size 2 prism layers will. be located at all walls The size of the hub shroud and nowalls parts is 2 5 and remains so. for two layers away from the surface tetra width To finish press Apply then Dismiss. The last step of the mesh setup will be a setup of elements sizes on two curves at the. trailing edge of the impeller In the Main Toolbar click Mesh Curve Mesh Setup For. the two curves indicated in Fig 16 set the parameter Number of nodes to 8. Now the mesh can be computed In the Main Toolbar click Mesh Compute Mesh. In the Compute Mesh window turn on creation of prism layers and mesh hexa core after. the tetra meshing Fig 11 Press Compute At the trailing edge the mesh will look like as. presented in Fig 12, Since the prism elements consist of only one layer we have to subdivide it In the Main. Toolbar click Edit Mesh Split Mesh Set the parameters according to Fig 20 Prism. Volume Parts BODY IMPELLER click on the icon No of layers 5 Click Apply After. wards the mesh at the outlet from the impeller will look like as presented in Fig 13 Note. in general there should be 10 15 prism layers in the boundary layer due to wall function. requirements, Check the mesh for errors Click Edit Mesh Check Mesh Click Apply A pop. up window appears select the two periodic parts and click Accept Confirm the deletion of. unconnected vertices click Yes, Check the quality of the mesh Click Edit Mesh Display Mesh Quality The mesh. quality is below 0 2, Improve the mesh quality Click Edit Mesh Smooth Mesh Globally Set the. A S kerlavaj E Nobile January 2018,4 2 Computational grid 2 13.
Figure 17 Global mesh setup for the impeller blade.


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