Week 4 Challenge : CFD Meshing for BMW car

Aim: To perform 2D and volumetric Mesh on the given model

Procedure:

1. When viewed in PID mode, a lot of single cons are present and topo should be given immediately
2. The cons resolution is not good, the shapes are not accurate.
3. Use the Fine option in auxiliaries and give perfect shapes to cons
4. To perform this operation on a larger scale, Mesh→Length→set length as 1mm→Set macros as 1 mm
5. Since the model is nearly symmetric, the symmetry option can be used to mesh the other part
6. To use the symmetry option: Transfer→copy→Entity→Middle click→Symmetry→Chosses a plane
7. Right-click to deselect
8. Delete the other side except the symbol using the delete option
9. Six volumes will be created, the volume inside the car, the Volume inside 4 wheels, the volume between the car and the wind tunnel
10. The surface outside the car is bothered and not inside
11. The inside surface is deleted so that there won't be any triple cons in the outside surface(Triple cons create unwanted volume)
12. Two closely placed single cons can be pasted to double-cone
13. If a triple cone is present despite only 2 surfaces joining, there may be a small surface present which can be deleted by selecting all surfaces in that region and deselecting bigger visible surfaces
14. To retrieve any deleted surface do undelete
15. Two cons can be extended to meet at a cone by selecting the cones and the respective faces where they are present
16. There shouldn't be any volume formed inside any specific feature
17. delete unwanted hotpoints to get the desired shape
18. If there is a bubble present release that hot point
19. The surface exposed to airflow is colored grey using the orient option in the faces
20. If multiple cross edges are present there will be multiple surfaces
21. Use the project cut option to cut in a perpendicular manner
22. The heal cut option from the right bottom is chosen while using the cut operation while cutting through a curved plane
23. Sharp corners must also be avoided on the end surfaces
24. If the preview of both coons and fitted are not good small surface must be created part by part
25. Remove close cuts so as not to make any problems while the volumetric mesh
26. By now lights, emblem, grill, and glass are done. (Topo clean up)
27. If there is complicated surface to create, create smaller conjointed surfaces
28. The model must be closed completely from outside
29. There must be a common volume through out the car
30. Four tyres will have four different volumes and the car will have another separate volume
31. do not create small surfaces because they may cause problem in meshing, instead delee adjacent surfaces and create a new bigger surface
32. Do checks on geometry to make sure the geometry is having no errors
33. Delete the vertical surfaces where tyre is coming in contact with
34. cons to curve option is used from curves to imprint the curve on the model if when the face is deleted
35. All distorted surfaces are deleted
36. And curves are made through the edge middle part as a reminder of the previous shape
37. First delete surfaces interfering with the wheel
38. The more number of surface the more accurate the surface will be
39. There are common volumes present in the silencer, which will be considered while doing 3-D mesh
40. Delete all unchecked surfaces: uncheck on the screen→right click→show only
41. After removing all single cons except the plane of symmetry, check with only enabling single cons, and after that use geometric checks
42. Check the preview of the single cons and make sure they are from the plane of symmetry
43. There is a triple cone present. Release the cone→Delete unnecessary hot points→Topo→Triple cone no longer presents
44. A needle surface is also present. Check its neighbors and delete it.
45. Topological clean-up ends here.
46. Proceed to assign PIDs
47. To apply PID isolate that part using the PID region
48. To see the assigned color of the PID choose PIOD in draw mode
49. PIDs named body, lights, windows, wheels and rim, optical rearview mirror, grills, silencer, and logo are created
50. All the PIDs are assigned except the body and the rest of the model is assigned to the body
51. To delete the rest of the PIDs compress them
52. The next step is to give mesh length to each PID
53. Tetra CFD elements are used to give volumetric mesh
54. Insert the OPENFOAM deck in the window, beside the volumetric mesh
55. Provide quality criteria at the topo
56. Shells are 2D elements and solids are 3D elements(In Quality criteria)
57. Tria elements are used but tria alone cannot be enabled in quality criteria, so quad is also kept
58. Quality criteria and Mesh parameters can be saved with respective mesh parameters
59. While meshing the body, the target length is given in 3mm in mesh parameters
60. Measure the distance between smaller surfaces that may fail the quality criteria of min. length and remove the cut using cut→Right click
61. Delete the least significant cone in the previous step
62. Delete unnecessary hotpoints that may fail quality criteria
63. Double cons are shown as green lines in the mesh
64. There shouldn't be any parallel lines too
65. The visibility of the stored measurements can be changed from the database side box. Double click will give detailed information on the stored distances.
66. See the smallest distance in every PID and give the min and max mesh length accordingly
67. After topo clean-up quality criteria and mesh parameters are given
68. The skewness and angle values must be the same throughout the models
69. Tri element type is chosen
70. Give length as 1mm in perimeter and macro in mesh(for logo)
71. Mesh generation>spot mesh>visible
72. Go to hidden mode, entity view, wire
73. Reconstruct>off: To reduce the number of off elements
74. Deleting the hot points in mesh mode is favored over topo mode because it doesn't delete mesh
75. Grills are meshed with .3 min length, 3 max length, and 1 target mesh length
76. Logo meshed with .4 min length, 3 max length, and 1 target length
77. For window PID, 2 target length, 1 min length and 3 max length
78. For lights PID, target length is 4, 3 min length and 5 max length
79. The off elements for light PID is mainly max length
80. Give mesh parameters, target length average to get rid of these off-elements
81. Elements>Split: To split meshed trias
82. Right-click to take icons outside
83. Shell Mesh>Smooth: To reduce off elements
84. Grid>Move>Free: To move the node with respect to XYZ coordinates
85. Grid>Move>Guide: To move the node with respect to the surface
86. Spit and move the nodes
87. Split and smooth(easiest)
88. Move surface is used here
89. Grid>Origin: To undo the move option
90. For Rims and Tyre PID, 2 target length, 1 min length, and 3 max length
91. PIDs with no contact with each other are meshed first. So body PID is kept to mesh the last
92. Grids>Paste: To paste one node to the other
93. Macro>Cut>In the options list, choose macros, join, reconstruct in the mesh section, and choose the cut to delete to remove the off elements(in the mesh window)
94. To delete the cons in topo mode to get rid of off elements min length, create a cut to keep the shape and delete the cone
95. Show only the unmeshed surface give spot mesh and reconstruct
96. Delete the most unnecessary cut
97. For silencer PID, the target length is 3, 1 min length, and 5 max length
98. For rearview mirror PID, the target length is 2, 1 min length, and 3 max length
99. For body PID, the target length is 3, 1 min length and 5 max length
100. Only give mesh to macros as the body PID comes in contact with other PIDs with different mesh target lengths and check whether the other mesh still exists or not
101. Give only perimeter length and remove the line in contact with 2 different PIDs
102. Another approach is to give spot mesh without giving perimeter or macros. This will create smaller elements near other PIDs and the majority be 3 mm target length(creating 1 mm mesh throughout)
103. Erase> visible: To erase a mesh
104. After getting rid of off elements in the body PID, the symmetry option is used to complete the model
105. Set view using View> Top view
106. Transform> Copy> Entities > Symmetry> Mirror 3 point plane> Select 3 points to define the symmetry > Finish
107. Paste the single cons if present in the plane of symmetry
108. Delete hot point in mesh while keeping the mesh
109. If a surface is deleted while pasting the cons mesh them
110. The perimeter length while just choosing the surface will show the target length
111. Give spot mesh to the surface
112. Checks> Geometry> Enable unmeshed macros and single cons before doing volumetric mesh
113. The wind tunnel is when the car moves how the air around it interacts with the car, wind flow, etc
114. Create a wind tunnel and mesh it
115. The wind tunnel must start 4x distance from the front point of the car(x is the length of the car=1300mm)
116. Read face of the wind tunnel must be x distance from the back end of the car
117. The top face of the wind tunnel must be 3 x the distance from the car's top face and the bottom surface must be near the wheels(because CFD behavior is above the car not below the car)
118. The side faces of the wind tunnel must be x distance from the side ends of the car
119. Create new points and then new surfaces for the wind tunnel
120. Points> relative: To create points relative to the points on the surface
121. Dx, Dy, and Dz in relative can used to denote the direction like 0, 0, 1, and distance given below. The Z coordinate will take that distance in this case.
122. Curve> Create > Choose the points(and middle click): To create curves
123. Join the bottom end points using the curve
124. Create a surface using filled and assign it to a new PID BaseSurface_Tunnel
125. Faces> Offset: Used to create a surface with an offset
126. Delete all the curves and points made
127. Create PIDs nameli TopSurface_Tunnel, SideSurface_Tunnel, FrontFace_Tunnel, RearFace_Tunnel
128. Wind tunnel must be meshed with finer elements in regions near the car
129. Remove quality criteria and mesh the top surface with a 100 mm target length(both perimeter and macros)
130. The top surface has 100 mm mesh length and the bottom surface has 20 mm as mesh length
131. Perimeter> Spacing(Biasing> Geometric>Factor 1.1>dmin20>dlimit100): To give variable mesh length along a cone
132. Mesh every surface one by one
133. 15 and 25 is min and max lengths for the bottom surface
134. 80 and 120 is min and max lengths for the top surface
135. Then mesh other surfaces
136. For volumetric mesh, Volumes >Define >Autodetect
137. We are only interested in the volume between the wind tunnel and the car body
138. Delete unwanted volumes
139. RightClick>Remesh: To mesh the volume

Learning Outcome: Learned how to do surface cleanup. Learned to do surface and volumetric mesh with varying mesh lengths and for different PIDs with different mesh lengths. And to create a wind tunnel.

Result: The CFD analysis is conducted on the wind tunnel volume.

Conclusion: It is easy to use the symmetric option if surfaces are symmetric. It saves a lot of time doing topo cleanup. Wind tunnel volume is meshed to understand the CFD applications. Use smooth, reconstruct, split, move, and join if off elements are present while meshing due to quality criteria.

*The screenshots when added in this text space are causing trouble in loading and uploading. So they are attached below. Kindly look into it.

**The result file: https://drive.google.com/file/d/1yUnSYTzEg2Sli0UI6j55-Sd0E7kg0Fk4/view?usp=sharing