Week 4 Challenge : CFD Meshing for BMW car

AIM: CFD meshing in BMW car

Procedure:

To perform CFD meshing in BMW car by following steps:

1) Clear the geometrical errors/topo clean up

2)Assign PIDs

3)Surface meshing

4) Create Wind tunnel

5) Volumetric meshing

Step 1: Topo cleanup

• Open the BMW car in ANSA window; file---->Open
• Once the object is open check the resolution of the object; to change the smooth object we will go for Auxillary---> fine option and then click all the parts separately for smoothing otherwise select Mesh--> Length--->perimeter--->give as 1 mm
• As we noted, the given model BMW car looks symmetry other than logo.
• Select one side of the car and deselect the logo then delete that for easy operations.
• To perform the topo cleanup, isolate each parts and remove the single and double COONS.
• Initially we isolate the front grills parts, remove the errors using delete option, then making new faces wherever we need finally make it into a single volume.
• Following by front grills, will remove the geometrical errors in headlight section, logo, mirror, window, and tyres.
• Remove all the single and triple coons and clear the small sections, extra available parts which is not needed for meshing.
• While clearing the errors remove the unwanted hotpoints by hotpoints---->delete
• Finally to check all the parts are in double COONS with single volume.
• Check with all parts by check---> Geometry-->visible
• If any errors like sharp edges, triple COONS, intersection surfaces, clear all the errors.
• Once finish the topo cleanup in each parts geometry check should be done to check the hiding errors.
• Finally will do the topo cleanup in bottom of the car.
• Remove all the intersection errors, overlapping surfaces, extra surfaces, sharp edges in the floor.
• To create the new surface, we have to make one reference line by clicking curves-->Cons2Curves option.
• Then create small faces by creating hot points, then click Faces---> new; if there is any small holes use fill hole option to create the surface.

  Fig 1 (a) Logo

  

  Fig 1 (b) (i) Grills

  

  Fig 1 (b) (ii) Grills

  

  Fig 1 (b) (iii) grills

  

  Fig 1 (c) (i) Mirror

  

  Fig 1 (c) (ii) Rear Side mirror

  

  Fig 1 (d) Door Lock

  Step 2: Assign PID:

  • After finishing the topo cleanup, will generate PID assign the parts in the model (body, mirror, tyre, grills, window, silencer, logo, lights)
  • Remaining PIDs will be deleted by using Compress tool
  • 

    Fig 2: Assigning PID

    Step 3: Surface meshing:

    • Before meshing we will check the distance of the small parts, if it is smaller than 1 mm, hide the part by cut option.
    • Then isolate each part and assign the quality criteria; mesh parameters i.e. skewness, minimum and maximum target length as per the given data.
    • Mesh type as Tria
    • Make sure to remove the unwanted options in criteria
    • Give the perimeter, and macros length by selecting the parts
    • Then click mesh--->CFD mesh--> visible
    • select the hidden mode while doing meshing to check the off elements.
    • After meshing each part check the off elements and clear it by selecting mesh --->shell mesh-->reconstruct or left click near to off then select the improve option ---->reconstruct/reshape/smooth/fix quality to reduce the error
    • If it is a small error then select grids-->move option to move the modes and clear it.

      Fig 3 (a) After meshing: Logo

      

      Fig 3 (b) After Meshing: Grills

      

      Fig 3 (c) (i) After meshing: Lights back

      

      Fig 3 (c) (ii) After meshing: Lights Front side

      

      Fig 3 (d) (i) After Meshing: tyres

      `

      Fig 3 (d) (ii) After Meshing: tyres-clear view

      

      Fig 3 (e) Silencer: After meshing

      

      Fig 3 (f) Body

      

      Fig 3 (g) Final Model After surface meshing

      Perform symmetry

      • After finishing the meshing without off elements will do the symmetry option.
      • Select the Transform---> copy--->Entities--> select obeject--> select the three axis---> finish
      • The half of the car should be placed symmetrically
      • check the single coons and remove it by paste option.
      • 

        Fig 3 (h) Model after Symmetry

        Step 4: Generating wind tunnel

        • To generate the wind tunnel select the reference point select points--> relative and give the points as per the given data
        • Create the new faces of the wind tunnel
        • Generate the PIDs of the new faces
        • Create the meshing by giving quality criteria and meshing parameters
        • 

          Fig 4 (a): Wind tunnel

          

          Fig 4 (b) Wind tunnel after meshing

          Step 5: Volumetric meshing

          After finishing the surface mesh, will perform volumetric mesh; v.mesh---> define

          Initially define the parameters ; whichever no need, delete the surface; out of all the surface we select only one surface for volumetric meshing.

          Due to compuatational range, the volumetric meshing can't generate in normal windows.

        • 

          Fig 5: Final model before Volumetric meshing