Tutorial: 2D Pipe Junction Using Hexa Meshing
Contents
1. Move Vertex Method Single vj Vertex Movement Constraints Fin FEY FixZ Fix direction r Move dependent zj Apply IER Dismiss a Click S Select vert s and move the vertices Figure 13 Select the Vertex Keeping the left mouse button pressed drag the vertex along the curve ANSYS Inc February 11 2010 13 2D Pipe Junction Using Hexa Meshing 14 pc Figure 13 Moving Vertices Notes e Due to the associations made between the edges and curves many of these vertices will snap to the correct position Vertices can also be moved along the curve by dragging the mouse To capture the ends of the curves 1 Select the vertex 4 Keep left mouse button pressed and drag the vertex along the curve until the vertex can be moved no further 11 Position the cursor beyond the end of the curve so that the end is surely captured You may also prefer to associate the vertex with the points at the ends of the curves as described later in step 3 The ends of the pipe are straight and it 1s possible to block this example without using the curve associations However the curve associations also create line elements on curves they are associated to If you skip performing the curve associations the boundary line elements will not be created This will make it impossible to apply boundary conditions to that edge such as inlet or wall Hence most CFD solvers give errors if any of the perimete2. c Click S Vertices d Select Select all appropriate visible objects 60 from the selection tool bar You can also enter v for all visible vertices or drag a box to select all vertices e Click middle mouse button to accept the selection f Click for the Ref Edges g Select the edges 13 34 and 34 42 and click middle mouse button to accept the selection This selection chooses the 1 and 7 index at each vertex for matching h Click Apply i Disable Pre Mesh and re enable it Blocking Pre Mesh The Mesh dialog box will appear asking if you want to recompute the mesh Click Yes Figures 20 and 21 show the comparison of mesh before and after matching the edges I UN Ne LH Y JR JOR EI SOAK BEKA Ay AY X f y M SS SONS YI rn EES KRY oe ESR NS RY y ANAN OS SOS LOS ETA ALS SRS TRE meee Be oe ne ee a Ho er nde cd 2222 s SE f W t 52191137 Figure 20 Mesh Before Edge Matching O ANSYS Inc February 11 2010 25 2D Pipe Junction Using Hexa Meshing BEI TT i H TH AR RR B Figure 21 Final Mesh After Edge Matching 3 Check the quality of the mesh gt Pre Mesh Quality Histograms Pre Mesh Quality a Criterion Determinant JII Histogram Options Mines v
3. box the suggests that you have to click the right mouse button to enable or disable an option here Numbers Rms j Numbers For detailed information about GUI and text conventions refer to the document Getting otarted with ANSYS ICEM CFD Preparation 1 Download the hexa 2dpipe FILES zip file from the ANSYS Customer Por tal It contains the necessary input geometry file hexa 2dpipe tin 2 Start ANSYS ICEM CFD and open the geometry hexa_2dpipe tin File gt Geometry gt Open Geometry 2 ANSYS Inc February 11 2010 2D Pipe Junction Using Hexa Meshing Blocking Strategy Decide the blocking strategy to generate a mesh with blocking Figure 2 The Mesh and Topologies Note The geometry is equivalent to a T shape You need to bend the right side of the blocking crossbar upward to resemble the geometry See Figure 2 To fit the T shaped blocking material to the geometry do the following Create associations between the Edges of the blocks and the Curves in the geometry 2 Move the Vertices of the blocks to the corners of the geometry Now the mesh sizes is set and the mesh is computed The program will automatically project the edge nodes onto the curves of the geometry and the internal 2D volume mesh will be interpolated O ANSYS Inc February 11 2010 3 2D Pipe Junction Using Hexa Meshing Step 1 Blocking the Geometry Create initial block a Initialize the 2D bloc
4. Curve DEZ 3 Similarly associate the edges 41 42 43 44 to CURVES 3 4 and 8 The blue cyan edges 42 43 34 42 38 43 do not have to be associated They are internal and will interpolate on the geometry when the mesh is computed 4 Verify that the correct associations have been set Figure 12 Blocking nws Edges rws Show association Figure 12 Projection of Edges to Curve The green arrows in the display point from an edge to its associated curve Nodes and vertices of these edges will project on to the associated geometry 12 O ANSYS Inc February 11 2010 2D Pipe Junction Using Hexa Meshing Note After completion if the associations do not appear correctly you can asso ciate the edges to the correct curves again It 1s not necessary to disassociate and then re associate Associating the edge to a new curve will overwrite the previous association The steps of operation can also be retraced using Undo and Redo buttons 5 Deselect Show association Blocking nws Edges rws Show association Step 3 Moving the Vertices 1 Manually move the vertices of inlets and outlet ends of large pipe gt Move Vertex e Move Vertex Note Selecting Move Vertex from the function tabs will prompt you to select from the screen It 1s usually not necessary to select Move Vertex from the DEZ unless another option was previously selected Move Vertices Move Vertices a
5. D geometry You should first select edges and then curves to which you want to associate the edges If two or more curves are selected per operation those curves will automatically be grouped concatenated For reference select Show Curve Names 5ee Figure 11 Geometry nws 9 Curves rus Show Curve Names This 1s not required for edge to curve association but it helps to illustrate the fact that each blocking edge is associated to named curve s URVES 1 Figure 11 Vertex Numbers and Curve Names 1 Associate the inlet the leftmost end of the large pipe gt Associate ig gt Associate Edge to Curve a Select the required edges i Ensure that Project vertices are disabled default ii Click Select edge s Select edge 13 41 iv Click the middle mouse button to accept the selection 10 O ANSYS Inc February 11 2010 2D Pipe Junction Using Hexa Meshing Blocking Associations a Edit Associations gt og Uo 8 Associate Edge gt Curve Edae s 41130 Curves CURVES AS Project vertices Project ta surface intersection Project ends ta curve intersection Apply ok Dismiss b Select the appropriate curves i Click amp Select compcurve s ii Select the curve CURVES 1 11 Click the middle mouse button to accept the selection c Click Apply in the Associate Edge gt Curve DEZ The associated edge will tu
6. Tutorial 2D Pipe Junction Using Hexa Meshing Introduction In this tutorial you will generate a mesh for a two dimensional pipe junction composed of two inlets and one outlet After generating an initial mesh you will check the quality of the mesh and refine it for a Navier Stokes solution Figure 1 2D Pipe Geometry This tutorial demonstrates how to do the following e Blocking the geometry e Associating to geometry e Moving the vertices e Applying mesh parameters e Generating the mesh e Adjusting the edge distribution and refining the mesh e Matching the edges e Verifying and saving the mesh O ANSYS Inc February 11 2010 1 2D Pipe Junction Using Hexa Meshing Prerequisites This tutorial assumes that you are familiar with the menu structure in ANSYS ICEM CFD and that you have read about this functionality Some of the steps in setup and the procedure will not be shown explicitly For details about hexa mesh generation refer to the Chapter Hexa in ANSYS ICEM CFD user manual Conventions Some of the basic conventions used in this tutorial are e The icon to the left of the text here Blocking suggests that you have to select the option from the display tree Blocking e The arrow mark with the text LMB in the box the suggests that you have to click the left mouse button to enable or disable an option here Vertices ims Vertices e The arrow mark with the text RMB in the
7. alue Marsi value Mast height D 3 Hum of bars to y Only visible indes range Active parts only Apply IE Dismiss a Retain the default settings b Click Apply c Select the worst two bars from the histogram The selected bars will be highlighted in pink Figure 22 Determinant 3x3x3 0 01 02 03 04 05 06 OF 05 03 1 Figure 22 Histogram 26 ANSYS Inc February 11 2010 2D Pipe Junction Using Hexa Meshing The highlighted elements are shown in Figure 23 or Sa EIEEE E H 31 Figure 23 Worst Quality Elements Highlighted Step 8 Verifying and Saving the Mesh 1 Save the mesh in unstructured format Pre Mesh gt Convert to Unstruct Mesh 2 Save the blocking file 2D pipe geometry final blk File gt Blocking gt Save Blocking As This block file can be loaded in a future session File gt Blocking gt Open Blocking for additional modification or to mesh a similar geometry Save each blocking to a separate file instead of overwriting a previous one In more complex models you may have to back track and load a previous blocking Save the project file 2D pipe geometry final prj File gt Save Project As This will save all the files tetin blocking and unstructured mesh 4 Exit the current session File gt Exit ANSYS Inc February 11 2010 27 2D Pipe Junction Using Hexa Mes
8. ax size found along that index Hence it may vary slightly from Figure 15 In this step you will use advanced edge meshing features to re distribute grid points to resolve the salient features of the flow 1 Disable Pre Mesh Blocking rms Pre Mesh 2 Re display Curves and Edges 3 See the distribution of grid points along the edges Figure 16 Blocking rms gt Edges ims gt Bunching ANSYS Inc February 11 2010 2D Pipe Junction Using Hexa Meshing Figure 16 Bunching the Edges 4 Reduce the number of nodes along the length of the large pipe Blocking Vertices rus Numbers a Display the edge meshing parameters Blocking gt Pre Mesh Params 9 gt Edge Params IN b Select Select edge s s or Edge Params IN and select edge 13 34 when prompted c In the Pre Mesh Params DEZ change the number of Nodes to 27 Click Apply P Pre Hesh Params Meshing Parameters GON Edge 1334 1 S Length 42 4466 Nodes p Mesh law BiGeometic Spacing 1 D 1 63256 Spl Linked Select Reverse Ratio 1 1 Spacing 2 D 1 63256 Sp2Linked Select Reverse Ratio2 2 Max Space nh 1 63256 Spacing Relative Nodes Locked Apply Dismiss 19 O ANSYS Inc February 11 2010 2D Pipe Junction Using Hexa Meshing 20 5 Similarly re select IN or s select edge 21 38 change Nodes to 27 and click Apply 6 Enable Pre Mesh and recompute t
9. de spacing on the end of the target edge that connects to the reference edge to match the node spacing on the reference edge gt Pre Mesh Params gt Match Edges S 1 Match the edge spacing manually a Select Selected from the Method drop down list b Click for the Reference Edge c Select the edge 42 43 and click middle mouse button to accept the selection d Click for the Target Edge s O ANSYS Inc February 11 2010 23 2D Pipe Junction Using Hexa Meshing Pre Hesh Params a Heshing Parameters 96 9 Match Edge spacing Method Selected Reference Edge 42 43 AS Target Edge s Im 42111 AB ue Link spacing ml Apply o Dismiss e Select the edges 41 42 and 42 33 and click middle mouse button to accept the selection f Click Apply in the Match Edge spacing DEZ g Enable Pre Mesh Blocking rms Pre Mesh The Mesh dialog box will appear asking if you want to recompute the mesh Click Yes 2 Match the edge spacing automatically a Select Automatic from the Method drop down list Pre Mesh Params Heshing Parameters P INNA Hatch Edge spacing Method Automatic E Vertices 33 37 41 42 43 44 o Spacing Minimum Match Edges Dimension Selected C All Ref Edges 13341 423 Ag D ismiss b Ensure that the Spacing is Minimum El 24 ANSYS Inc February 11 2010 2D Pipe Junction Using Hexa Meshing
10. elect Update All This will automatically determine the number of nodes on the edges from the mesh sizes set on the curves b Click Apply 2 Enable Pre Mesh Blocking ims Pre Mesh The Mesh dialog box will appear asking if you want to recompute the mesh Click s Mesh is currently out af date recompute es Ma He mesh out of date parts He mesh specific parts 3 Disable Edges and Vertices Blocking zms Edges Blocking rms gt Vertices The initial mesh 15 shown in Figure 15 O ANSYS Inc February 11 2010 17 2D Pipe Junction Using Hexa Meshing Step 6 Adjusting the Edge Distribution and Refining the Mesh 18 LS ee eh cee ee ee rere eee ee ree rer gll ee HE Se aia a sy EN AN a Sr se Se a i obi or EH CAS EA A AEN NN dae RR eod E RTT PRRREESSERRER As See eS CQ Aue Rs SOD NEAR FA Too RAO COR AR M Das A MEE NARERARRERTRERRREXUEERR ANS ad Pe UT A FEET AAAS R RR LE AARNE ARE A T Men av m PEL OAS m DOM LE MENLTANARAARRATENEL DUE LAA ee Rei HE TR ER AREA SEDE E Id Lid L Figure 15 The Initial Mesh pre eee eee Note The number of elements in initial mesh 1s sensitive to exact vertex placement longest edge length in an index divided by m
11. esh Params DEZ enter 0 5 for Spacing 1 and Spacing 2 Note Spacing 1 refers to the node spacing at the beginning of the edge and Spacing 2 refers to the spacing at the end of the edge The begin ning of the edge is shown by the white arrow after the edge 1 selected ii Enter 1 2 for Ratio 1 and Ratio 2 ii Click Apply Requested values for spacing and ratio are entered in the first column Ac tual values are displayed in the second column The requested ratios cannot be attained due to the number of Nodes Mesh law Spacingl and Spacing2 Increase the number of Nodes using the arrow until the ratios are close to the entered value 1 2 Note The Mesh law is by default set to BiGeometric This allows the nodes to be biased towards both ends of the edge The expansion rate from the end is a linear progression Several other mathematical progression functions laws are available b Ensure that the parallel edges 34 42 38 43 and 21 44 have the same spacing i Enable Copy Parameters in the Pre Mesh Params DEZ ii Ensure that To All Parallel Edges is selected from Method drop down list ii Click Apply O ANSYS Inc February 11 2010 21 2D Pipe Junction Using Hexa Meshing c Select edge 21 38 and enter 0 5 for Spacing 1 and Spacing 2 and click Apply This will concentrate grid points toward the outlet and toward the small pipe To have these changes reflected in edge 43 44 as well ensure that To All Parallel Edge
12. g gt Curve Mesh Setup ES gt Select curve s amp 1 Select Select all appropriate visible objects You can enter v for visible or a for all 2 Set Maximum size to 1 Curve Mesh Setup Curve Mesh Parameters Method General gt Select Curve s CURVES 5 amp Maximum size 1 Number of nodes Height 0 Height ratio 0 Mum of layers 0 Ie Tetra width 0 Min size limit 0 deviation 0 Advanced Bunching Bunching law Spacing 1 Ratio 1 Spacing 2 PO Ratio 2 6 Curve direction Dismiss from the selection tool bar e Maximum size determines the length of the edges on the curve or surface for 3D e Height determines the length of the edge of the first layer normal to the curve e Ratio Ratio 1 and Ratio 2 determines the normal heights of the subsequent layers In this case height and ratio are determined by the perpendicular curves whose Maximum size will override any height or ratio settings 3 Ignore all other parameters and click Apply 16 ANSYS Inc February 11 2010 2D Pipe Junction Using Hexa Meshing Step 5 Generating the Mesh In this step you will generate an initial mesh Pre Mesh Params 9 gt Update Sizes Pre Mesh Params a TNS Recalculate Sizes Hethod Update All Keep Distributions Keep Counts Lurve Edge bunching 1 Enable Update Sizes a S
13. hing 28 ANSYS Inc February 11 2010
14. king Blocking gt Create Block EA gt Initialize Blocks Create Block 2 Part LIVE l Create Block ZA en Initialize Blocks Type 2D Planar ok Dismiss i Enter LIVE in the Part field ii Change the Type to 2D Planar ii Click Apply 5 v D lt D ct D Un 5 Qu D z UJ O ga Blocking zms Vertices c Select Numbers under Vertices Blocking Vertices rus Numbers Subsets F Ee On surfaces Fe Penodic Bh Mames a T Froj type Part Indices w Numbers Show Vertex Infa Figure 39 Numbering the Vertices O ANSYS Inc February 11 2010 2D Pipe Junction Using Hexa Meshing The white block encloses the geometry as shown in Figure 4 This initial block will be used to create the topology of the model pi The curves are now colored separately instead of by part This is done so that the individual curve entities can be distinguished from each other which is necessary for some of the blocking operations You can enable or disable the color coding by doing the following 1 Select Curves in the Model display control tree Figure 4 Initial FLUID Block ii Select deselect Show Composite Geometry rms gt Curves rws 9 Show Composite 2 Split the initial block into sub blocks In this case you will first do two vertical splits and one horizontal s
15. o view the new mesh PF SS eee TF en EP T T UG ERFEFERFEFFEFEIFAEREFBEF es ze M EELS Se FP Fn p re T CO P TT reer rier B ee DU zu tal E s DU ra Ta Ca a EL air m am iz ee cro 2 229 D Te D 2s oe 25 at zw anen l SQ 08 0 133760136 EX mc M ANA E AE e ons Se a es OT S TOC EQ DE 25 Dr VELA m UEM Um a RR RE di Em LLL LI Werer r r Figure 17 Edges Parameter Note Figure 17 shows a structured grid When the number of nodes is changed on one edge all parallel opposing edges will automatically have the same number of nodes In this case edges 41 42 and 43 44 will have the same number of nodes as edges 13 34 and 38 21 respectively 7 Disable Pre Mesh and Curves to view the bunching on the edges See Figure 18 Blocking rms gt Pre Mesh Geometry rms gt Curves ANSYS Inc February 11 2010 2D Pipe Junction Using Hexa Meshing Figure 18 Bunching on Edges After Changing the Number of Nodes 8 Bias the nodes closer to the wall boundaries of the large pipe a Click and select edge 13 41 i In the Pre M
16. plit a Create verticle split i Ensure that Curves under Geometry is enabled Geometry rms gt Curves ii Retain default selection of Screen select from the Split Method drop down list in Split Block DEZ ANSYS Inc February 11 2010 2D Pipe Junction Using Hexa Meshing Split Block icd Split Block gt Split Block Block Select f AllVisible Selected Edge 1119 1 AZ Copy distribution from nearest parallel edge Project vertices Split Method Split Method Screen select Ned D ismiss Figure 5 The Split Window Note Jn this case the split may be done by approximation because only the topology of the T shape is essential the exact proportion is not iii Click s Select edge s You will be prompted to select an edge red text at the bottom of the view screen iv Select the edge defined by vertices 11 and 19 or 13 and 21 v lo position the new edge click the left mouse button slide the new edge to the desired location and click middle mouse button The split is shown in Figure 6 Check the color of the edge blue cyan designates an internal edge 6 O ANSYS Inc February 11 2010 2D Pipe Junction Using Hexa Meshing Figure 6 First Split Edge 11 19 Note cancel the previous selection click the right mouse button while in selection mode vi Similarly select the edge defined by vertices 33 and 19 or 34 and 21 See Fig
17. r edges are not associated with perimeter curves 2 Move the remaining vertices to their appropriate positions on the geometry See Figure 14 Try to make the blocks as orthogonal good internal angles as possible ANSYS Inc February 11 2010 2D Pipe Junction Using Hexa Meshing Figure 14 Moving Rest of the Vertices to Their Position 3 Associate the vertices to the points This 1s am optional step a Select Show Point Names Geometry rms gt Points 5 Show Point Names b Enable Associate Vertex 4 Blocking gt Associate e gt Associate Vertex de The Point option 1s enabled by default AE C x Select the Vertex and select the Point to which you want to associate the vertex Associate the vertices 13 21 41 42 33 37 43 44 to points POINTS 2 POINTS 5 POINTS 1 POINTS 10 POINTS 9 POINTS 8 POINTS 11 POINTS 6 e Deselect Show Point Names e Geometry rms gt Points rms gt Show Point Names 4 Save the blocking File gt Blocking gt Save Blocking As 5 Provide a filename 2D pipe geometry b1k so that the file can be reloaded at a later time using File gt Blocking gt Open Blocking O ANSYS Inc February 11 2010 15 2D Pipe Junction Using Hexa Meshing Step 4 Applying Mesh Parameters Set Mesh parameters sizes on the geometry curves in this 2D case This is done at the geometry level and can be done before or after the blockin
18. rn green Note Associate edge to curve operation runs in continuation mode allowing you to select the next set of edges and curves without reinvoking the function The function will be cancelled if you click the middle mouse button or click Dismiss without selecting entities 2 Similarly associate the following edge curve combinations to make the T fit the geometry e For small pipe associate the following Edge 33 42 to curve CURVES 10 Edge 33 37 to CURVES 11 Edge 37 43 to CURVES 9 e For outlet top horizontal end of large pipe associate the following Edge 21 44 to CURVES T This vertical edge will eventually be moved to capture the horizontal curve Note When the entities are overlapped with other entities disable the entity types This will enable you to identify the right entity For example disable Vertices and Edges to verify the curve names Enable the Edges to proceed with the selection O ANSYS Inc February 11 2010 11 2D Pipe Junction Using Hexa Meshing e For large pipe associate the following a Select all three edges 13 34 34 38 and 38 21 and click the middle mouse button to confirm the selection b Select the three curves CURVES 2 CURVES 5 and CURVES 6 and click the middle mouse button The three curves will automatically be grouped as one logical composite entity Geometrically they are still three separate curves c Click Apply in the Associate Edge gt
19. s is selected from Method drop down list 9 Copy the same distribution to the other section of the large pipe a Select To Selected Edges Reversed from the Method drop down list b Select the Select edge s s icon immediately underneath the Method field c Select the edge 13 34 d Click the middle mouse button or click Apply 10 Refine the nodes along the small pipe a Click Select edge s icon toward the top of the menu and select the edge 33 42 b Enter 9 for the Nodes in the DEZ c Enter 1 0 and 0 5 for Spacing 1 and Spacing 2 respectively d Select To All Parallel Edges from the Method drop down list e Click Apply 11 Select edge 34 38 and enter 9 for the Nodes Click Apply 12 Enable Pre Mesh and recompute to view the refined mesh shown in Figure 19 Blocking rms gt Pre Mesh 22 O ANSYS Inc February 11 2010 2D Pipe Junction Using Hexa Meshing diac DT Cg x T ST Te ee ce ey NENNEN eT RE 1 rox NN C a a C u s rr 2 Sh Tm e ETE MERECE oe wo i Ls m E RUNE ga 1 ee m 20 01 1o n Ss 26 Tq Figure 19 The Refined Mesh Step 7 Matching the Edges In this step you will match the edge spacing of a Reference Edge to a connecting Target Edge s You will modify the no
20. ure 7 Figure 7 Second Split Edge 33 19 O ANSYS Inc February 11 2010 7 2D Pipe Junction Using Hexa Meshing b Create horizontal split i Change Split Method to Relative in Split Block DEZ ii Enter 0 5 for the value of Parameter mid point of selected edge ii Select any one of the four vertical edges in the graphics window and click Apply The horizontal split 1s shown in Figure 8 1 J o L Figure 8 Curves and FLUID Block After Three Splits 3 Delete unnecessary blocks The next step in this top doun approach is to remove delete the blocks those are not required gt Delete Block 9 a Disable Delete permanently b Click Ls Select block s c Select the blocks to be deleted as shown in Figure 9 and click the middle mouse button to accept the selection 8 ANSYS Inc February 11 2010 2D Pipe Junction Using Hexa Meshing blocks to he deleted Figure 9 Blocks to be Deleted d Click Apply in the Delete Block DEZ Note The deleted blocks with Delete permanently disabled default are actu ally put into the VORFN part a default dead zone that is usually deacti vated The geometry and blocking of the model now resemble Figure 10 1 T i Figure 10 Final T Shape Topology O ANSYS Inc February 11 2010 9 2D Pipe Junction Using Hexa Meshing Step 2 Associating to Geometry In this step you will associate edges of the blocking to the curves of the CA
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