Week 4 Challenge : CFD Meshing for BMW car
AIM :
CFD Mesing For BMW car .
OBJECTIVE :
To learn topology , geometry clean-up,mesing for BMW car. Also perform meshing with the given Target length and elements quality criteria. Aftar meshing the half model, Do symmetry to the other side.
Target lengths for the different parts of a model are as follow:
1. Body - 3 mm
2. Light - 4 mm
3. Grills - 1 mm
4. Rims and tyar - 2 mm
5. Optical Rear view mirror - 2 mm
6. Wndow - 2 mm
7. Silencer - 3 mm
8. Logo - 1 mm
Initial Model
First of all cut the model into a half
PROCEDURE :
1) Our Model have so many single cons so apply topo to entire model and topo will work, itwill joins the two or three cons together respectively .
2) As our model has uneven surfaces so to make the surfaces fine use fine option from auxiliaries . If we have to do cons ressolution of entire model
in one shot then go to mesh desk and apply perimeters and macros equal to 1mm so that it will improve cons resolutions of the entire model. It will
ultimately reduces the distance between two cons which equal to 1mm in order to make surface finish.
3) If two single cons are near to each other then we can join them by using paste option.
4) Topo cleanup for grills is done by deleting unnecessary surfaces from grills to remove triple cons, deleting un-wanted hot points , and single cons are removing by patching the new surfaces using New-Cons/Fitted optios.
5) Topo cleanup tyre's and side mirror and head and tail light, includes triple cons by deleting the unwanted surfaces.
6) For a logo the overlapped surfaces were identified and seperated by projecting the surfaces on hood and are deleted following by removing small edges which may cause error during meshing.
7) Lower car body need to corrected by removing unwanted overlapped parts and the lower body intersecting with tyres need to be deleted to make tyres as a free volume keeping track of different parts in the lower body 'con2curve' is used to have blueprint are deleted surfaces with the help of which new surfaces are created.
8) Geometric checks are perfomed to have no single cons present in the model and possible triple cons are removed by deleting it using universal delete option.
9) Before creating surface mesh the cons and small edges that have length less than minimum mesh length are identified by measuring the distance between cons and solved using 'cut' option in order to avoid mesh failing the mesh criteria at this small surfaces.
10) PIDs are assigned using the PID manager which is present top deck for all parts in the body.
SURFACE MESHING :
First of all wisely choose the Quality criteria parameters which are only required : -
1) Individual elements are meshed with respective mesh length with minimum and maximum length.
2) Grills are isolated and give a mesh length of 1mm with minimum and maximum length of 0.5mm and 2mm with triangular elements and for Quality criteria provide appropriate mesh length. Here are quality criteria's and mesh element size for all the components.
BMW LOGO
GRILLS
BODY
SILENCER
WINDOWS
3) The mesh is seen in Hidden Mode and ENT wise, which will show off elements which are violating the criteria. So we need to remove off elements by using options such as MOVE, SPLIT, RECONSTRUCT,SMOOTH the grid respectively ,from this we can improve our meshing.
BMW logo
Meshing of Grill
Meshing of Silencer
Meshing of tyres
Meshing of Lights
Meshing of Rear reflected mirror
Meshing of windows
4) Once the off elements's number reduced to 0 then meshing is done successfully, and Similar method is used for other PID's.
5) Symmetry need to be performed on the other half of car in which the all the components with mesh are copied directly to the other side using Transform option from the top side option list.
WIND TUNNEL :
Data for wind tunnel are as follow:
The wind tunnel dimensions are, if x is the lengths of car then
Front of wind tunnel is 4X from the car.
Rear of wind tunnel is 6X from the car.
Top of wind tunnel is 3X from the car.
Side walls of wind tunnel are at X from the side portion of the car
Bottom of wind tunnel is in close proximity of wheels
Points are created by using 'Reative option' in points of Topo Deck.
Total length of the Car
Create point at front
Create point at bottom
Move point at -75 of the dx
Create point at Rear
Create point at Top
Create point at right side
Do curve to joint points
Topo Deck- points - relative - points - select points. After the points are created join these points from bottom plane by 'create curvesb'
Once the curves are created for top and bottom then create a surface with help of 'New' option in 'faces'
Topo - Faces- New -Fitted -will open PID manager window-create new PID -double click on it to create surface on it.
As the analysis of what happens over the surfaces of car is of importance so the bottom of wind tunnel should have good resolution as compare to the top portion as it relatively at larger distance than botttom. So mesh length of 20 is taken at bottom and 100 for top portion.
As the front and rear of car are connected with the top and bottom surfaces then the mesh length for this surfaces should vary from 20 to 100 from bottom to top portion. This gradual variation can be achieved using Spacing option from the perimeters section of Mesh deck.
Perimeters- Spacing -Geometric -factor of 1.1 and d-min of 20 successful application of this will be indicated by upward pointing arrows.
Mesh is generated by applying Spot mesh for individual surfaces.
Learning Outcomes :
1. Learnt the complete CFD meshing skills from skratch.
2. Performed various topo clean-ups using different tools.
3. Understood the need of double cons and removing unecessary triple and singel cons.
4. The use of symmetry helps in reducing the work time and help in having accurate results with less work.
5. Create surfaces using references hot points by using relative points.
6. Suraface meshing for different components and their varying mesh lengths.
7. Using spacing option in surface meshing helps in having varying mesh lengths along the surfaces.
8. Using re-construct option to reduce off elements to a level where we can edited it manually.
9. Using the mesh modifying tools like move, split and smooth options.
Results :
Complete car model with wind tunnel ANSA file drive
https://drive.google.com/file/d/1VIk9WN68s1wxaVbAomWgTQPc3ynSm9Tt/view?usp=sharing
Conclusions :
1. BMW car model is topo cleaned and surface meshed appropriately.
2. Wind tunnel is created and suraface meshed with reference to the car model size.
3. Different Volumes of the car model is created since the silencer and tyres are not connected to the car body.
4. Single volume is created of the car body so that it can be avoided at one go when creating a volumetric mesh.
5. Required physics tests can be performed on the wind tunnel volume model after volumetric meshing successfully.