Week 4 Challenge : CFD Meshing for BMW car

AIM :

To perform the surface mesh for the given BMW car model and also for the fluid domain enclosure which is used for CFD analysis.

OBJECTIVES :

• To check for any geometric errors in the half portion of the given BMW car model (Since, the given car model is symmetric about z-axis, Half portion of the given car model is deleted and Thus, after performing surface mesh for the the remaining half, it can be transformed to a complete one) and to do the respective topological clean ups.
• To asssign PIDs(Property identifier) for different parts of the given BMW car model.
• To perform surface meshing with different target lengths and quality criterias for different PIDs as follows,

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
   

• To create the fluid domain for the given BMW car model.
• To perform the surface mesh for the domain, and to get the domain region ready for fluid analysis.
  

Tools used :

MENUBAR>Drawing Styles>Shadow - This flag turns on and off the shadow drawing style.

MENUBAR>Drawing Styles>Wire - This flag activates the wire model representation of the geometry and the FE-Model.

MENUBAR>Faces Draw>Cross Hatches - This flag activates and deactivates the visibility of Faces' cross-hatches. As this flag is activated, green isoparametric lines that lie on the visible Faces appear. If the Faces are linked Faces the color of the crosshatch is orange.

MENUBAR>Tools>Checks>Checks Manager - This function opens the Checks Manager. It is used to execute massively a number of checks.

MENUBAR>Tools>Checks>Geometry - This function locates geometrical problems of the model such as Unmeshed Macros, Unchecked Faces, Needle Faces, Collapsed Cons, Triple Cons, Overlaps and Cracks.

MENUBAR>Tools>Checks>Penetration [Intersections] - This function checks all visible shell elements, macros, solids skin (the outer area of a solid volume), thick-shells, gaskets and all combinations of them to locate any intersections. For this check, the shell elements' thickness is not taken into account. The results are reported in the 'Checks' list window that appears.

MENUBAR>Faces Draw>Single - This flag activates and deactivates the visibility of single (red) CONS.

TOPO>CONS>Project - This function projects, as CONS or 3D Curves, a number of selected 3D-curves, CONS, element edges, line elements or Hexa Box edges on a number of selected Faces, in a user controlled direction. The selection of the CONS or 3D-curves can be assisted by the 'Corner Angle', 'PID Neighbs' for line elements or 'Path'.

MENUBAR>Utilities>Delete - The Delete function of the Geometry Group can be used to delete various ANSA entities (Curves, Faces, FE-Model entities etc.).

TOPO>Hot Points>Insert - This function creates or projects Hot Points by hovering positions on CONS or 3d curves or 1d FE elements.

MENUBAR>Utilities>Transform - This function is used to Translate, Rotate, Transform, Scale, Symmetry or Mirror selected entities (Faces, Points, Elements etc). The selected entities are copied in the new position.
Symmetry: This function creates symmetric entities. At the drop down menu there are the options to use the default symmetry plane or the current working plane or select from the screen the symmetry point, axis or plane that is going to be used.

TOPO>CONS>Fill Hole - This function fills holes on Faces. The holes can be of any shape. Such internal openings can be selected individually, or automatically among the visible ones if they fall below a user specified diameter value. There is the option to create automatically 3D Curves, Points or Connection Points of the removed holes, in order to mark their shape and position for reference.

TOPO>Hot Points>Project - This function defines a new Hot Point that lies on a CONS (or a Node on a 3D-curve) as the projection of an existing Node, 3D-point, Hot Point, Weld Spot etc.
This function also defines a new Weld Spot that lies on a face as the projection of an existing node, 3D-point etc. to this face.

TOPO>CONS>Release - This function releases CONS which have been automatically joined (pasted) or were joined by the CONS>Paste function.

TOPO>Hot Points>Release - This function releases Hot Points that lie on the limit of two or more faces. When a Hot Point is released, the adjacent CONS of the faces' limits are also released and become single CONS (marked in red). As a result, the local topology changes

TOPO>Faces>New - This function defines a new surface by selecting its boundary curves and creates a corresponding face that covers the new surface. The calculated surface appears as a net.

New [COONS] -

This function defines a new multi-patch Face and Surface, using the COONS interpolation principal. This is an easy way to define a new surface by its boundary curves. After the mathematical definition is finished, the calculated surface appears as a net. A relative window gives the ability to accept or to reject the calculated surface. When only three boundary sides are selected, there is the ability to choose between two alternative definitions for the fourth generated side, one is to be straight and the other is to have a shape similar to its opposite side.

New [EXISTING SURF] -

This function defines a new Face laying on an existing surface.

New [PLANAR] -

This function defines a new planar face. The underlying surface is automatically created.

New [FITTED] -

The FITTED option is used for the definition of a non-planar Face. The created Face fits to the selected boundaries.

TOPO>Faces>Cut - This function cuts (splits) an existing Face or joins faces if inverse operation is applied (right mouse button).
It does not require the existence of Hot Points since it can be applied directly on an arbitrary position of a CONS.

TOPO>Faces>Proj.Cut - This function is used to cut (split) a Face by combining the Hot Points>Project and Faces>Cut functions. In other words, it splits a face between a selected hot point and its projection on a selected CONS.

MENUBAR>Feature Selection>Line Options>Loop - Selects a closed loop of edges, perimeters or curves. Any internal or external perimeter is considered a loop.

MENUBAR>Feature Selection>ENT - Selects any kind of entity (the kind of entity depends on the ANSA function which is in use) one by one or multiple entities by box selection.

MENUBAR>Feature Selection>Surface Options>PID Region - If the 'PID Region' flag is activated, then by picking an element (shell or solid) of a particular PID, ANSA automatically selects all the connected visible elements, which are assigned with the particular PID.

MENUBAR>Focus>Or - Keep visible only the selected entities.

MENUBAR>Focus>And - Select one or more already visible entities, in order to also bring to visible any neighbor entities which may exist.

MENUBAR>Focus>Not - Hide one or more selected entities.

MENUBAR>Focus>!Not - Select entities that will remain visible. The selected entities temporarily (during selection) are excluded from the visible ones, but as soon as 'Enter' or the middle mouse is pressed (selections' termination) then they will only be the ones to remain visible in the graphics area.

MENUBAR>Focus>Invert - Inverts the current visibility status. This means that visible entities become non-visible and non-visible entities become visible. If one or more Parts are Locked then this function operates exclusively in the Locked Parts.

MENUBAR>Focus>All - Bring to visible all entities of the database. If the Lock flag button is active, then the function brings to visible only the entities that belong to the active locked view.
If there are numerous stored locked views, then they will be displayed as a sub-options list of the All button.

MENUBAR>Focus>Lock - This function locks the current working area view. This working area view is kept locked until the flag is turned off. There is also the ability to store different kinds of views of the same model. The status and the content of the working area influence the result of the All function.

MENUBAR>Focus>Neighb - Logical operation that brings to visible all the 1st level neighboring items attached to the already visible ones.

TOPO>Hot Points>Release - This function releases Hot Points that lie on the limit of two or more faces. When a Hot Point is released, the adjacent CONS of the faces' limits are also released and become single CONS (marked in red). As a result, the local topology changes.

TOPO>Faces>Topo - This function automatically creates topological conditions between selected adjacent CONS.

TOPO>Faces>Extend - This function extends Faces (source), according to a specified distance or until they reach a target Face or target group of Faces, by adding new Faces as extensions to the source ones. The new Faces' Surfaces are extensions of the Surfaces of the sources. Topology can be applied automatically, if required.

TOPO>Faces>Orient - This function sets a uniform orientation direction to all visible Faces according to the orientation of the majority of the Faces. The mesh elements that will be generated, or those already existing, also obtain a uniform orientation.

TOPO>CONS>Paste - This function pastes (joins together) two or more CONS segments that lie close to each other, and which usually are boundaries of different Faces. A new topological condition is created and these Faces become neighboring.

TOPO>Faces>Undelete - This function recovers a Face that was previously deleted, provided that the COMPRESS command was not used since the Face was deleted. As the Faces>Undelete function is activated, all deleted Faces still in the database become highlighted and can be selected for recovery.

TOPO>Faces>Intersect - This function defines the intersection between two groups of Faces and/or FE elements that penetrate each other. Topology can be applied automatically if required. In case that the two groups can define a closed volume between them, Boolean operations can be applied.

TOPO>Hot Points>Delete - This function deletes Hot Points lying on a CONS segment. After deletion, the adjacent CONS segments sharing the Hot Point become one.

TOPO>Points>New[Num.Input] - This function defines new 3D-points (cyan squares) by their (x,y,z) coordinates. As the function is activated, a window appears that allows the numerical input of these values.

TOPO>Points>Relative - This function defines new 3D-points that lie on a given relative position from a number of selected 3D-points, Hot Points, Weld Points etc. The input of a (dx, dy, dz) vector, or an indication by the mouse is required for the definition of the relative position.

TOPO>Curves>Cons2Curves - This function defines 3D-curves from existing CONS, shell/solid edges, Line Elements end Cross-sections.

TOPO>Curves>Create - This function creates smooth 3D-curves, polylines, circles and ellipses, by defining a number of points with the help of geometric and element entities (e.g., Faces, CONS, Curves, Nodes, Elements, Working Planes e.t.c).

MENUBAR>Lists>Properties - This function facilitates property management. A list of the properties existing in the file is available. Management windows, such as this one, provide filtering, sorting and selection capabilities on the listed entities as well as definition of new entities.

MENUBAR>Utilities>Mesh Parameters - This function opens the 'Mesh Parameters' window, where the user can define the parameters for the Reconstruction, Reshape and Fix functions.

MENUBAR>Utilities>Quality criteria - Select and set the respective quality criteria for the corresponding elements to perform the Quality Checks (Hidden Mode). Also set the general presentation settings concerning the ANSA workspace.

MESH>Perimeters>Length - This function defines the element length on selected perimeter segments or macro areas. The element length may be explicitly declared or may be declared as a factor to be multiplied by the existing element length.

MESH>Mesh Generation>CFD - This function is recommended after the user has applied the Perimeters>Spacing(Auto CFD) on the selected perimeters.
This algorithm meshes with variable element length, depending on the local curvature of the underlying CAD surface, under tight user-controlled specifications. It generated the less possible elements taking into account all small details of the geometry. This algorithm is an advanced meshing algorithm tailor made to meet CFD specs or other application areas where a variable size mesh is required.

MESH>Perimeters>Spacing[Manual] - In cases where there are element length variations in the model between neighboring Macro Areas, it is useful to control this transition and make it smooth using biasing (Spacing) functions along Perimeter Segments. There are three available node-biasing modes in ANSA, linear, geometric and bell curve. This function can be applied only on CONS, if there is no CONS in the model, the function is not activated.

MENUBAR>Utilities>Measure - This function performs various measurements according to the corresponding Selection Mode. The applied measurements can be saved and viewed at a later stage.

MESH>Shell Mesh>Improve - The function is applied on either meshed Macro Areas or FE models in order to improve the existing mesh. The user can select one of the embedded algorithms: Reconstruct, Reshape, Smooth or Fix Quality.

Reshape,

The Shell Mesh>Reshape function is applied on either meshed Macro Areas or FE models to improve mesh quality. The function performs automatically a combination of the following actions:

- Joins Perimeters
- Inserts or Deletes Hot Points
- Reconstructs the mesh
- Creates quad zones around holes based on predefined rules.

Reconstruct,

The Re-construction function is a powerful tool for the creation of a high quality surface mesh. It examines a given mesh and performs re-meshing to correct problematic areas and optimize the overall quality of the mesh according to the mesh parameters. For Geometry Mesh (Macro Areas) all modifications are made on the underlying CAD surface.

For FE-model mesh, all modifications are made on the surface defined by the shell elements. The function may be applied to selected or to all visible meshed Macro Areas and FEM mesh according to the chosen option.

With the option "Advanced" the Advanced Selection window opens where the user selects where to apply the Reconstruction. Note that the option "Violating" is associated with the Mesh Quality criteria in the F11 card whereas, all the rest obey to the Mesh Parameters. The Expand Level controls the number of zones around the affected elements.

Applied on Geometry mesh the perimeters will be visible as feature lines, which cannot change, but the user can add or remove more edges as perimeters. Applied on FE mesh, the user is able to modify all feature lines during preview stage.

MESH>Elements>Split - This function splits quadrilateral and triangular shell elements into smaller ones. Element splitting is performed between selected nodes and/or inserted nodes along selected element edges. The function can be applied on individual or groups of shell elements in order to improve the mesh orientation, reduce the number of triangles, or refine locally or globally the mesh of a part. Refer to ANSA User's Guide for a detailed description of the use of the function.

MENUBAR>Utilities>Compress - This function is used to compress an ANSA database. Compression may be selectively applied either on geometric entities only (faces, curves 3D-points) or on the entire database. By this operation, all information concerning deleted entities is lost. Therefore no undelete operation can be made upon entities which were deleted prior to the compress operation. This function relieves the database from unwanted information. Also, this function removes from the database all grid points, coordinate systems, properties and materials that are defined but not used in the model element definition.

MESH>Macros>Freeze/Un - This function locks/unlocks the selected Macro Areas and their boundary segments. In this way, the Macro Areas' condition is stabilized and no participation to functions that might alter their topology or meshing (if any) is permitted. If any function tries to alter the Macro Area, or a Macro Area's component is selected to participate to another function, a relative message appears in the text window.

VOLUME MESH>Volumes>Define[Auto Detect] - This function automatically defines multiple volumes using already meshed macros or FE-model mesh.

VOLUME MESH>Volumes>List - This function enables the handling of the defined volumes in the database.

VOLUME MESH>Unstructured Mesh>Tetra CFD - The Tetra CFD algorithm is most suited for geometries of thick volumes, large domains with significant variation in length of the surface mesh (say more than 2 orders of magnitude). Most met in CFD applications.
Activate Tetra CFD and select either one or more already defined volumes or some specific solid elements.

MENUBAR>Utilities>Snapshot - Take snapshots from the drawing area or from any ANSA window. Depending on the selected option the image can be: POSTSCRIPT, RGB, TIFF, JPEG, PNG or BMP.

PROCEDURE :

STEP 1 : Open the given BMW car model using MENUBAR>File>Open

STEP 2 : Since the given car model has the coarse geometry, the geometry has been made smooth, which is done by defining the mesh length for entire perimeter of the given car model as 1mm by using MESH>Perimeters>Length

STEP 3 : Since the given car model is symmetric about z-axis, delete half portion of the car except the BMW logo region using MENUBAR>Utilities>Delete

STEP 4 : Now, Check for the geometric errors in the remaining regions using MENUBAR>Tools>Checks>Checks Manager

STEP 5 : Since the given model is mainly to perform the surface mesh for CFD analysis (in this case, fluid domain is over the external surface of the car for making aerodynamic analysis), the external surface is made positive by using TOPO>Faces>Orient

STEP 6 : The given car model has more geometrical errors, so, isolate every region individually and perform the topological clean up. First, isolate the front grill using MENUBAR>Focus>!Not and check for geometric errors in it using MENUBAR>Tools>Checks>Checks Manager

STEP 7 : Delete all the overlapping surfaces that forms the triple cons and the unwanted surfaces ( the internal car surfaces can be deleted, since the fluid domain is over the external surface, also the internal car volume should be a single one).

STEP 8 : Extend the side grill surfaces to the back surface using TOPO>Faces>Extend inorder to delete the unwanted internal surfaces and also project the cons using TOPO>CONS>Project to the side surface, inorder to delete the remaining unwanted internal surfaces.

STEP 9 : After performing the topological clean up for the grill, Re-check the grill for any geometric errors using MENUBAR>Tools>Checks>Checks Manager

STEP 10 : Next, Isolate the front head light region and check for any geometric errors using MENUBAR>Tools>Checks>Checks Manager, inorder to perfom the topo clean up in it.

STEP 11 : Delete all the overlapping surfaces that forms triple cons and also the unwanted internal surfaces

STEP 12 : Since, there is a gap between the two surfaces, paste those single cons using TOPO>CONS>Paste and after doing all the topological clean ups, verify it using MENUBAR>Tools>Checks>Checks Manager

STEP 13 : Next, Isolate the mirror region and perform the check using MENUBAR>Tools>Checks>Checks Manager

STEP 14 : Delete all the overlapping and unwanted internal surfaces using MENUBAR>Utilities>Delete and after performing all the clean up, recheck the geometry using MENUBAR>Tools>Checks>Checks Manager

STEP 15 : Next, Isolate the side grill part and find out all the geometric errors in it using MENUBAR>Tools>Checks>Checks Manager

STEP 16 : Delete all the overlapping, unchecked and unwanted internal surfaces using MENUBAR>Utilities>Delete

STEP 17 : Re-check again using MENUBAR>Tools>Checks>Checks Manager

STEP 18 : Next, Isolate the BMW logo part and find the geometric errors in it

STEP 19 : Since, there are more overlapping surfaces, delete all those surfaces using MENUBAR>Utilities>Delete

STEP 20 : Inorder to create a new surface, use TOPO>Faces>New

STEP 21 : Since, some of the surfaces on the letter 'M' and 'W' have very small lengths compared to the mesh lengths, which will affect the mesh. Delete those and create new surfaces.

STEP 22 : Re-check the logo part for any geometric errors using MENUBAR>Tools>Checks>Checks Manager

STEP 23 : Isolate the door lock region of the car model and check for any geometric errors in it.

STEP 24 : After performing the geometric clean ups, once again, check for errors using MENUBAR>Tools>Checks>Checks Manager

STEP 25 : Delete the overlapping and internal surfaces which form the triple cons in the window regions of the car model.

STEP 26 : Delete the overlapping and internal surfaces which form the triple cons in the rear light regions of the car model.

STEP 27 : Isolate the rear part of the car model and perform the geometric check.

STEP 28 : Delete the unwanted internal and intersecting surfaces in that region.

STEP 29 : After doing all the topo clean ups, re-verify it using MENUBAR>Tools>Checks>Checks Manager

STEP 30 : Next, Isolate the rims and tyres region and check for geometric errors in it.

STEP 31 : Delete all the overlapping surfaces that form the triple cons.

STEP 32 : Create new surface to close the tyres volume using TOPO>Faces>New, repeat the same for the remaining tyre also.

STEP 33 : After doing all the topological clean up in the region, re-check the geometry using MENUBAR>Tools>Checks>Checks Manager

STEP 34 : Isolate the silencer part of the given car model and release the cons present at the inner surfaces of the exhaust.

STEP 35 : Delete the inner region of the silencer by choosing PID region for selecting the entities.

STEP 36 : Now, close the silencer volume using TOPO>CONS>Fill Hole and check for any geometric errors.

STEP 37 : Next, Isolate the last grill region and perform the geometric check in it.

STEP 38 : Delete all the surfaces that form the triple cons in the region.

STEP 39 : Project the single con in the top surface to the grill surfaces using TOPO>CONS>Project

STEP 40 : Now, delete all those unwanted extra entities present in the grill.

STEP 41 : Create new surfaces using TOPO>Faces>New to enclose the grill region from the external surface.

STEP 42 : Once again, verify the grill section for any geometric errors after doing all the topological clean up.

STEP 43 : Isolate the bottom surface of the car model and check for geometric errors in it using MENUBAR>Tools>Checks>Checks Manager

STEP 44 : Before deleting the unwanted surfaces, create curves to the edge of the surface using TOPO>Curves>Cons2Curves

STEP 45 : Now, delete all the penetrating, overlapping and unwanted internal surfaces.

STEP 46 : Create new surfaces for the bottom using the curves that are created before.

STEP 47 : Isolate the door handle and perform the geometric check in it.

STEP 48 : To remove the concave cons error, make a cut at the door handle using TOPO>Faces>Cut and delete the surface and create the new surface.

STEP 49 : Assign PIDS for every region of the given car model using MENUBAR>Lists>Properties

STEP 50 : Finally, Re-check the geometric errors for the whole model using MENUBAR>Tools>Checks>Checks Manager

STEP 51 : Now, the car model is ready to get transformed as full. To do that, First hide logo PID and use MENUBAR>Utilities>Transform, in it, select the entities to get transformed, press enter, choose the mirror 3 points plane under symmetry and select any three points on the end surface of the car model and again press enter

STEP 52 : Now, the car model has been transformed.

STEP 53 : Once again, perform the geometric check to check for any errors in the model.

STEP 54 : To perform surface mesh for different PIDs with different mesh target lengths, Isolate the PIDs individually. First, Isolate the grills and logo PIDs , and give minimum and maximum mesh target length as 0.5 and 2 mm respectively under MENUBAR>Utilities>Mesh Parameters

STEP 55 : Now, give the mesh length as 1 mm in perimeter and macros using MESH>Perimeters>Length

STEP 56 : Perform the CFD surface mesh by using MESH>Mesh Generation>CFD. Since, there are more off elements present in the PIDs after meshing, use MESH>Shell Mesh>Improve to reduce the off elements.

STEP 57 : Freeze the meshed PIDs using MESH>Macros>Freeze/Un, inorder to use different mesh lengths for other PIDs .

STEP 58 : Isolate the Windows, optical rear view mirror and tyres PIDs , and give minimum and maximum mesh target length as 0.5 and 2.5 mm respectively under MENUBAR>Utilities>Mesh Parameters.Then, give the mesh length as 2 mm in perimeter and macros using MESH>Perimeters>Length

STEP 59 : Perform the CFD surface mesh by using MESH>Mesh Generation>CFD. Since, there are more off elements present in the PIDs after meshing, use MESH>Shell Mesh>Improve to reduce the off elements. Freeze the meshed PIDs using MESH>Macros>Freeze/Un, inorder to use different mesh lengths for other PIDs

STEP 60 : Isolate the body and silencer PIDs , and give minimum and maximum mesh target length as 0.5 and 4 mm respectively under MENUBAR>Utilities>Mesh Parameters. Then, give the mesh length as 3 mm in perimeter and macros using MESH>Perimeters>Length

STEP 61 : Perform the CFD surface mesh by using MESH>Mesh Generation>CFD. Since, there are more off elements present in the PIDs after meshing, use MESH>Shell Mesh>Improve to reduce the off elements. Freeze the meshed PIDs using MESH>Macros>Freeze/Un, inorder to use different mesh lengths for other PIDs

STEP 62 : Isolate the lights PID , and give minimum and maximum mesh target length as 0.5 and 4.5 mm respectively under MENUBAR>Utilities>Mesh Parameters. Then, give the mesh length as 4 mm in perimeter and macros using MESH>Perimeters>Length

STEP 63 : Perform the CFD surface mesh by using MESH>Mesh Generation>CFD. Since, there are more off elements present in the PIDs after meshing, use MESH>Shell Mesh>Improve to reduce the off elements. Freeze the meshed PIDs using MESH>Macros>Freeze/Un, inorder to use different mesh lengths for other PIDs

STEP 64 : In order to create a fluid domain, First, measure the length of the car model, width and height of the car model using MENUBAR>Utilities>Measure

STEP 65 : The fluid domain enclosure should be of length,

• for the front domain, 4*length of the car model, distance taken from the front of the car model.
• for the rear domain, 6*length of the car model, distance taken from the front of the car model .
• for the top domain, 3*height of the car model, distance taken from the top surface of the car model.
• for the bottom domain, since the CFD analysis is not important compared to others surfaces, it can be held near to the bottom surface.
• for the side domains, width of the car model, distance taken from each respective sides.

STEP 66 : Inorder to create the fluid domain enclosure, Create 3D points using TOPO>Points>Relative to the respective lengths as shown

STEP 67 : Then, create curves to join those points using TOPO>Curves>Create

STEP 68 : Now, create the surfaces using TOPO>Faces>New to enclose the model and assign PIDs to each surface of the domain.

STEP 69 : Surface mesh should be performed for different domain regions with different mesh lengths. First, Isolate the Top domain PID and give the perimeter length as 100 mm using MESH>Perimeters>Length

STEP 70 : Next, Isolate the bottom domain PID and give the perimeter length as 20 mm using MESH>Perimeters>Length

STEP 71 : For the front, rear and side domains, use MESH>Perimeters>Spacing[Manual] with 'dmin' as 20 mm and 'dlimit' as 10 mm with factor 1.1 , and choose the four cons at sides with the arrors pointing upwards.

STEP 72 : Now, perform the surface mesh using MESH>Mesh Generation>CFD for the fluid domain.

STEP 73 : Inorder to perform volumetric mesh, first, define the volumes using VOLUME MESH>Volumes>Define[Auto Detect]

STEP 74 : Delete the unwanted volumes where the fluid analysis is not done, select the domain volume between car model and the enclosure which is used for CFD analysis.

RESULTS :

Thus, the given car model is surface meshed and it is ready for volumetric meshing in the fluid domain area.

Google drive link for the final surface meshed fluid domain and the given BMW car model :

https://drive.google.com/file/d/1E9lj80ra6dRl41LqbURh7rZId_sGhf9b/view?usp=sharing

1. Screenshot of the given BMW car model after performing surface mesh,

2. Screenshot of the fluid domain after performing surface mesh,

CONCLUSION :

Hence, the volumetric mesh for the fluid domain takes more computational time(almost two days depending upon on the processor also) for the given BMW model with the given mesh target lengths. So, in order to reduce the computational time, the fluid domain can be created near to the model and mesh lengths can be provided as given and, away from the model, the fluid domain can be created with larger mesh lengths. This generates finer mesh elements near to the car surface and coarse mesh away from it.