Week 4 Challenge : CFD Meshing for BMW car

CFD Meshing for BMW car

Aim: By reducing the errors in the model and meshing the different components with different criteria using ANSA software. The overall aim is to generate the volumetric mesh between the BMW M6 car and wind tunnel.

Introduction:

The BMW M6 is a high-performance version of the 6 Series marketed under the BMW M sub-brand from 1983 to 2018. It’s a 4 seater with 4395 cc Petrol engine and 8-speed gear Automatic transmission 8 Gears, Paddle Shift, Sport Mode.

Procedure:

• Open ANSA software and input the model to the software.
• Go to tools-check-geometry-enable single cons-and execute
• The software will execute the different single cons present in the model.
• Now in order to reduce this single on the whole model is a bitty task hence we should delete the half part and work on it, then after reducing the errors, by using the symmetry option we can reduce single cons and triple cons on the whole model
• The portions the single cons & triple cons are present in the regions are Logo, Grills, Rear view mirror, Rim & Tyres, Lights, some cons on the Body regions.
• Majorly triple cons are present due to extra surfaces created one layer on the above.
• Going on the each location where the triple cons are located and analyse it and universal delete option to delete the unwanted layers.
• In order to make volumetric mesh the whole inside the car model should be one volume.
• By keeping this on mind, by going on each location where the single are present analyse it and work on it to reduce the single cons to double cons
• By isolating the parts where the single and triple cons are present we can work on it.
• First by choosing the grills portion and isolating it the below figure shows the single and triple cons

• In the front portion of the car grill having some unwanted triple cons and the some surfaces are joined. By deleting those surfaces and creating a new surfaces will reduce this type of errors.
• In order have single volume inside the car the surface which is creating the own volume should be recognise and should be deleted.
• Finally there should not be single cons and double cons should be present in the grill portion this can be visualized from the wire frame mode by pressing the ctrl+shift button.
• The single cons present in the left side of the half model will be diminished once we do the symmetric option.

• Finally from all the grill section i am able to minimize the triple cons and single cons present in the grill region.
• And also i should able to make a common volume from grill section as shown in the above figures, that I am able check with the wire frame mode also.
• Next I move through the windows section and triple cons are present and analyse it and delete the extra surface and as soon we delete the surface the triple cons are changed to double cons.

• Next I work with logo section in order to work on it first Isolation should be done, there are triple cons are present there, by delete the extra surface the triple cons are diminish but the surface are connect to each other.
• Now if I want to delete the extra surface from that situation we need to project the cons to the bonnet so that the two surfaces will be separated now I am able to delete the surface easily.
• After delete the surface the triple cons are will be diminished similarly I can delete the other triple cons.
• And also in order to make a single volume inside the car some surface are restricting so we can delete the surface and create a new surfaces to make one volume inside it.

• After logo again from the bonnet grill there are some triple cons are present this will be the extra surface

• Since it has the open case from inside and the one volume inside car will not happen I should work on it.
• I have project one cons of the upper grill portion will be projected to the downer portion, and buy using the cut and project cut option I can create a cons wherever the cons are not present.
• After this we can delete the upper portion of the inside grill and will be deleted and generate the new surface to create a one single volume inside the car

• Next I move to handle where the inside body the surfaces are not correctly connected. So again we need to project the cons to delete the unwanted surfaces.

• Again in order to make a single volume any surfaces obstructing the single volume inside the car by analysing should be deleted if any.
• Again from outside there are triple cons are presented in handle position, so analysing it for any extra surfaces and delete the surfaces to diminish the triple cons.

• Next move on to the Rear view mirror from inside where the mirror will create a own volume which should not be there because only one volume should be there for entire car deleting the surfaces will give a common volume inside the car.

• Moving on to rim and tyres position a triple con is present due to additional surfaces which should be deleted. But the surfaces are interconnected. So again by creating new surface will be done to diminish the single cons.

• The same will be done with other tyre also.
• Next move on to the body the back side of the car there is triple con and will delete because of the additional surfaces present there.

• The next single con is present in between the body and the car bumper, this is because the surfaces between them are not intersected with each other.
• In order to make intersect, in faces- intersect option selecting the first group of faces and second group of faces and by doing middle click in mouse the faces will get separated and creating a triple con in that region. But again this triple con is because of additional surface present there.

• Similarly at the back side of the body and bumper there are some extra additional surfaces are present, by deleting it and creating a new surface by using coon’s options.

• Like this at the end of the of topo clean up the single cons and triple cons should be diminished and should be single volume inside the car, other than types portion because we are interested in only volume inside the car.

• Before going to the meshing we should again go to tools option and check the geometry for any other single cons or triple cons are present.
• The only single cons are present in the middle of the car after making symmetry option these single cons are converted into double cons.
• Now before moving to the mesh option we should create a proper property Id’s (PID) for the whole car.
• After creating PID we should assign the each PID with the respected body feature. The extra PID is deleted by using compress option. And only the main PID is kept for further process.

• After creating PID’s, moving on to the meshing part now.
• First we should do the surface mesh before moving to the volumetric mesh.
• By isolating the single PID’s and giving the quality criteria and meshing parameter I can able to do each PID’s meshing by using the given mesh length.
• First starting with LOGO, in quality criteria some parameters are to be included like skewness, minimum length, maximum length, quads options and should opt for FLUENT calculation mode in all off this option.
• For Logo the mesh length is 1mm, so we need to measure the minimum distance in logo first so that that minimum length will be given in the quality criteria.
• As per the design the minimum length in the logo is 0.41mm, so in quality criteria the minimum length given is 0.4 and maximum length given is 3mm, and in meshing parameter the target length of 1mm and Tria element type, and selecting the model of parameter and macros of 1mm.
• Now by using the spot mesh visible option the mesh will be done on the LOGO.

• Now due to some errors in the model there is skewness and minimum length error seen in the model this is called off elements, again go back in the topo clean-up and delete the unwanted extra surface and create a new surface.
• After that come back to the mesh option again remesh the model, the error will be diminished and the off elements should be zero at the end of meshing.

• Moving on to the Grills option of the same mesh length, isolating this PID, giving the model parameter and macros of 1 mm, meshing the model and check for the off elements, and this off elements should be zero and the end of the meshing.

• Next moving on to the windows PID, the element length given is 2mm. here in quality criteria the minimum length given is 1mm and maximum length is 3mm, and the Tria element type should be selected.

• And the off elements should be minimized by using spot mesh reconstruct option, if any off elements found after reconstruct option we can now use another option called grid move option here we will go to the off elements where it is located and the elements will be adjusted there so the nearby grid elements are adjusted and the off elements will be diminished.
• Move on to next PID is Rim and Tyres and isolating it, and the element length is 2mm, in the quality criteria the minimum length is 1mm and maximum length is 5mm, and the element type is Tria should be selected.

• And in the similar way rear view mirror mesh will be done.
• Move on to next PID is silencer and isolating it and the element length is 3mm, in the quality criteria the minimum length is 1mm and maximum length is 5mm, and the element type is Tria should be selected.
• Move on to next PID is Lights and isolating it and the element length is 4mm, in the quality criteria the minimum length is 3mm and maximum length is 5mm, and the element type is Tria should be selected.

• Move on to next PID is Body and isolating it and the element length is 3mm, in the quality criteria the minimum length is 1mm and maximum length is 5mm, and the element type is Tria should be selected.
• Now in this PID after meshing the body and bring back all the PID’s all together some other PID’s mesh will vanishes this is because variable mesh length between these PID’s.
• These PID’s are the mesh between Body and Rear view mirror, Windows, Grill, Logo and Light section. So before meshing this we should take proper care.
• Hence in order to keep both mesh all together wherever the joining between the body and the other PID’s the joining line should be disengage then only the whole meshing will generated with breaking.

• Moving on now the surface mesh has been generated without any disturbances, now we can very well make the symmetric option so that the full model will topo cleaned up and meshed.
• This can be done by using transform copy option in utilities bar. After selecting the transform copy option, by selecting the nodes at 3 different points the whole body will be symmetric at the centre and the body will generated.

• After making the symmetric option there is single cons is present on the windows section this is because the two single cons are joined together so by using the cons paste option we can very well convert this single cons into double cons.
• After this we can again very well check any single or triple cons are present in the model by using check the geometry option.
• There should not be any single cons or triple cons are present in the model.
• Now before going to the volumetric meshing we should generate the wind tunnel for the whole model so that we can generate the volumetric mesh between the wind tunnel and the car for the analysis purpose.
• We should create some points in order to generate the wind tunnel. This can be done by using points-relative option. The standards to create this points are in front portion of the body and wind tunnel should be four times the body size,
• similarly the back side is 6 times the body size and the top surface should be 3 times the body size, and the sides should be one times the body size, and the bottom side it be the tyres and the bottom surface should be joined.

• Next by using these points i can very well create a new surface by using fitted or coon’s option from new faces option in topo mode.

• After completing the creating the new surface around the model we can very well check this by wire frame mode.
• Before giving the mesh we need to create the PID,s for the wind tunnel, like top surface, bottom surface, side surfaces, front, rear surfaces.
• Now moving ahead meshing the wind tunnel giving the mesh parameters for top surfaces of 100mm mesh length and 20mm for bottom surfaces.
• Again for the side surfaces by using parametric spacing option, in meshing and selecting the geometry and D start of 20mm and D end of 100mm.

• By using spot mesh select option we can generate the mesh for the each surface.

• Moving ahead after completing the meshing for the model BMW M6 and the wind tunnel by analysing in the wire frame all mesh are generated without any off elements we can move ahead for volumetric mesh.
• In volumetric mesh define option for whole data base visible there are 7 volumes will be generated these are
  1. Volume between car & wind tunnel
  2. Volume inside the car
  3. Volume of the silencer
  4. Volume of 4 rim & tyres separately
• The volume between car & wind tunnel only be selected and generate the volumetric mesh and analyse for the further analysis.

  Result:

  Volumetric mesh has been generated for the given geometry with the help of ANSA software

  Conclusion:

  In order to analysis any flow properties within the geometry we should first check all the loop holes in the geometry and should minimize it by topo clean up the geometry. After topo clean-up we should generate the surface mesh without any off element in the model. Similarly we should mesh the wind tunnel also.Tetra CFD is 3D mesh tool option which is used for the volumetric mesh to analyse the flow in the given geometry.

  https://drive.google.com/file/d/12Q4dIve1upg3eF8MV5YHS8ExvnD-h6YU/view?usp=share_link

  **(As the file size is high i cant upload through the file upload option here so i am giving a link to check with the detailed report and the volumetric mesh model through this link.)