Week 4 Challenge : CFD Meshing for BMW car

Aim:

To check and solve all geometrical errors on half portion and Assign appropriate PIDs and also to Perform meshing with the given Target length and element Quality criteria. we also need to perform symentry and to create wind tunnel.

Given:

the target lengths given are

1. Body - 3 mm
2. Lights - 4 mm
3. Grills - 1 mm
4. Rims and Tyres - 2 mm
5. Optical Rear view mirror - 2 mm
6. Window - 2 mm
7. Silencer - 3 mm
8. Logo - 1 mm.

Also as per video skewness limit will be 0.5.

Procedure:

The following were the stages to perform

initial setup

Topological cleanup

check for errors

assigning PID's

component wise surface mesh

mirroring surfaces

creating wind tunnel

surface meshing wind tunnel

Volumetric meshing the whole components

1.Initial setup:

• initially we need to import to import the model into ANSA interface
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• then check for any geomentrical or surface errors vissible for example in tyre areas there is some error which shows oversizing of default meshing value
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• in order to rectify this type of error select all models and give mesh length to 1 mm which solves it
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• then select delete option and select half of the components by view in top view like
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• dont forget to deselect the logo which was commonly present
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• we further going to perform all the topological cleanup and meshing and then we gonna mirror it .

2.topological cleanup

• initially we gonna perform topo cleanup by resolving the issues such as single cons, triple cons and crack in model
• for topo cleanup we gonna make 4 seperate volumes such as car inner, tyres and silencer
• remember the concept there should be common volume inside car so all the excess faces abd volumes inside car can be neglected or deleted
• only outer surface of car should remain all the inner surface can be neglected
• please refer to the picture
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• all this inner components should be solved like this
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• like this picture components are soved for single, triple cons and errors
• for this we use tools such as delete, cut faces, new faces , cons paste , release option and topo cleanup.
• also hold ctrl and shift to see hidden frame views
• make sure to isolate each pid or components such as grills, logo, window, rear view mirror, silencer, wheels and rim and silencer and make sure for each selection you need to rectify error completely because if we misses it will be double work for us to perform meshing
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• make sure that final component should contain only double cons also check for interference of any face into any components and delete it

3.check for errors

after topo go to checks>> geomentry>>execute >> ehich shows any error in geomentry

reolve the issue if there is any like collapsed cons, single cons, triple cons , crack in surface ,etc.

Also go to checks >> checks manager >> PRE surface meshing checks to ensure that there is no errors related to factors for meshing

4.Assigning PID's

we need to assign each PID specifically

go to property manager right click>>new>> pshell>>pshell to create PID's accordingly

create the following PID like body; rms and tyres; grills ; logo; window;rear view mirror; light and silencer

apply each PID by apply option under specific PID

5.Component wise surface mesh:

initially go in following order which states to mesh body PID last

refer to the given details like

• Body - 3 mm
• Lights - 4 mm
• Grills - 1 mm
• Rims and Tyres - 2 mm
• Optical Rear view mirror - 2 mm
• Window - 2 mm
• Silencer - 3 mm
• Logo - 1 mm.

> Logo

• required target length for logo was 1mm
• isolate logo entities
• go to mesh parameters and provide target lengths as 1 mm and type as tria and save mesh parameters with name tag 1 mm mesh length
• go to quality criteria select skewness as 0.5; min length as 0.5; max length 2mm; angle parameters and also select calculation as fluent for all.
• go to classic mesh and length perimeters and select all components and give mesh length as 1mm and also macros as 1mm
• then also go to mesh >> spot mesh >> visible and click ok

• turn on hidden view to see the errors specify colors for each type of errors like min and max length ,skewness;
• red colour tria's are errors related to max length like wise green colour represents skewness and blue colour represents min length. you can also use reconstruct option to reduce no of errors
• when there is error go to grid >> move to move grid as a trial and error to rectify issues.

• you can also check the no of off values in bottom left corner
• click on offset and select show only to see only the offset values

• the colour represents only errors in skewness it can be rectified by using move option in mesh

• then make sure thAt there is no offset values
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repeat the same procedure for all the PID's except body PID the only difference is min; max length and target lengths as follows

• Lights - target length 4 mm min length 2mm ; max length 6mm:
• Grills - target length 1mm min length 2mm ; max length 6mm:
• Rims and Tyres - target length 2 mm min length 2mm ; max length 6mm:
• Optical Rear view mirror - target length 2 mm min length 2mm ; max length 6mm:
• Window -target length 2 mm min length 2mm ; max length 6mm:
• Silencer - target length 3 mm min length 2mm ; max length 6mm:

1. after all this PID's you only left with body PID.
2. for body PID assign min length as 1mm and max length as 5mm and target length as 3mm
3. also select all the surface and assume macros length as 3mm but change is for selecting areas for perimeter length select all the areas and deselect the edges or nodes in contact with other pid's and proceed further. which defines that there will be change in node length because body PID is the only one which in contact with other PID's.
4. if we define perimeter usually it will not completely mesh as there is change in target lengths.
5. then as usual perform spotmesh and click visible to mesh
6. check for errors and solve it as like other PID's.

6.Mirroring components

use copy option>>symentry>>select components to mirror>> three point plane >> select three points of plane to be as mirror>> click execute>>finish

7. Creating wind tunnel:

• for creating wind tunnel the factor is such that take the length of car as X
• space before car should be at 4X distance and behind car should be 6X distance
• each side it should be at X distance
• bottom should be at tyre location
• top surface should be at 3X distance.
• in order to create face click on points and relative and nodes give distance as 96mm
• which makes tyres intact with ground
• make another points using same tool before and after car with certain distance which makes a box like points
• use curve tools to create box and to create faces using those curves
• click on offset option and select the face and provide required height where surface need to be created
• close the gap of two faces with create faces on all four sides to make it as cuboid

• then create and assign PID like top , bottom , side , front and back side of wind tunnel on the created box
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8.Surface meshing wind tunnel

• go to mesh and mesh top surface with target length as 100mm and bottom surface as 20mm
• select spacing tool in perimeter option select four corners of box then assign values min length as 20mm and which increases as factor of 1.1 and also set limit as 100mm.
• perform mesh for remaining surfaces.
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as you can see that meshes at the bottom is so dense that it represents the target length of bottom or land phase is minimum and on the above it is larger in above

please be sure that meshing of every component is done before proceeding for volumetric mesh

9.volumetric mesh of components

select volumetric mesh>>define>>whole Db >> click on cfd mesh >>all

Result :

Thus the surface mesh of BMW car is performed and wind tunnel is created.

refer to the attached documents