Week 4 Challenge : CFD Meshing for BMW car

• AIM:-

To Perform and Study CFD Meshing for BMW Car Using ANSA.

• OBJECTIVES:-

To check and solve all geometrical errors on half portion and Assign appropriate PIDs. Perform meshing with the given Target length and element Quality criteria.

1. Target lengths for the different parts of a model are as follow:
2. Body - 3 mm
3. Lights - 4 mm
4. Grills - 1 mm
5. Rims and Tyres - 2 mm
6. Optical Rear view mirror - 2 mm
7. Window - 2 mm
8. Silencer - 3 mm
9. Logo - 1 mm

• PROCEDURE:-

BMW MODEL.

In this Project, We are going to Study and Perform CFD MESHING for BMW car. Some of the main components which is going to be Meshed, in this project is explained below.

• LOGO

BMW - Bayerische Motoren Werke. BMW was created in 1917 from the Munich firm Rapp-Motorenwerke.

• BODY SHELL.

The Vehicle Body Shell is a Functional backbone. It is the body of car that rest in the chassis and fits the Engine, Mechanical and Electrical components. It is deisgned to carry the weight of all components that present in the car.

• GRILLS.

Grills covers the front body of the vehicle and allows the Engine to cool. It sucks air through the grill which serve to provide the ventillation through the engine bay.

• WINDOWS.

The main reason for use of window glasses in cars is visbility. The visbilities managed by the cars are very useful.

• OPTICAL REAR VIEW MIRROR.

These mirrors are located on the exterior of the vehicles to help the driver see areas behind and side of the vehicle. The advantage of side mirrors being convex is that can get a wider view of each side of the car which helps reduce blind spots.

• RIMS AND TYRES.

The most basic and important parts of a car body that have always been in use are the wheels. These are circular forms that generate rotary motion and are responsible for moving the car from one point to another. The tire is the rubber part that wraps around the wheel and grips the road surface. Although the wheels can spin without tires, the car does not go very far. Without them, the wheels of the car would slip on the road faster without moving forward.

It is a decorative disc on an automobile wheel that covers the central part of the wheel. The function of the hubcap is to cover wheel hub and wheel fasteners to reduce the dirt and moisture collection. It also enhances the overall structure of the wheel.

• SILENCER.

The Outflow of the combustion gases creates the noise. The purpose of the silencer in the exhaust system is to reduce or dampen this noise.

• CFD - COMPUTATIONAL FLUID DYNAMICS.

Computational Fluid Dynamics Uses Numerical Solution methods which deals with the Prediction of Flow Physics for fluids, Mulitphases of Fluids, and Interation between Fluids and Solids.

• ANSA

Automatic Net Generation for Structural Analysis.

ANSA is a Computer Aided-Engineering tool for Finite Element Analysis and Computational Fluid Dynamic Analysis widely used in the Automotive Industries. It is developed by BETA CAE Systems. ANSA tools are mainly used in Automotive Industries to mesh Plastic/Sheet metal components for CFD analysis. Tool is used for Topology Cleanup, Meshing, Improving Mesh, Assigning Thickness and Preparing Solver Deck.

ANSA LAYOUT:-

• GEOMETRY.

To do a CFD Meshing for BMW car, First Step is to import the CAD model of a BMW car on a ANSA Spaceclaim. Once the CAD model is imported in the ANSA, most important step is to check the Single Cons and Triple Cons. Whenever Single cons and Triples are present TOPO CLEANUP needs to be done.

• TOPOLOGY CLEANUP

Topology is Geometry Consisting of Surface, Lines, Edges, etc which combines together and make CAD model. Topology cleanup is a process of fixing CAD model and making it ready for meshing process.

TOPO-CLEANUP Sets up tools for Geometry Cleanup and then Setting up the PIDs. Basically Our Geometry Model is in irregular Shape, including Overlapping Surfaces,CONS,etc. To Start the Topocleanup change PIDs setting into the Entity Model for better Understanding. Then Divide the CAD MODEL into Half as given geometry is Symmetric in Nature.

• ENTITY MODE.

• TYPES OF CONS.

There are Three types of CONS,

SINGLE CONS

DOUBLE CONS

TRIPLE CONS.

• CONS.

The edges in ANSA is called as CONs. Single cons are highlighted in the Red Color, Double Cons are in Yellow color. Triple Cons in Blue Color.

• CROSS-HATCH.

This allows the visualisation of Green lines along the center isoparameteries of the faces. Cross-hatch also used to select the green lines.

• OR `rarr` OR is used to Isolate the Surfaces.
• AND `rarr` It is Used to retrive the Connected Surface.
• NOT `rarr` NOT is similar to OR which is used to isolate the Surface but, need to double click the surfaces.
• ALL `rarr` ALL is used to retrive the all the hidden Surfaces of the Geometry.
• LOCK `rarr` LOCK is used to lock the Present Geometry.
• PID `rarr` PID is a Property ID which is Used to set the Boundary Conditions in the CFD.
• ENT `rarr` ENTITIES refers to Face, POINT, Curves, MESH ELEMENTS, etc.

We can able to See from the above Images, BMW car Specify irregular Shape, to overcome that errors we need to use the mesh tools and then select the perimeters give the length as 1mm to the Whole Geometry, so that the errors can be rectified and car shape will be in Finer Shape.

FINAL OUTPUT.

TRIPLE CONS.

Now, Next step is to cut the Geometry into half respectively as it is in Symmetric Shape, by cutting half of the geometric it will be easy to clear the CONs and OVERLAPPING surfaces, After finishing the TopoCleanup, Assigning the PIDs, Surface Meshing then with the Help of TRANSFORM tool by doing MIRROR option can replicate the Other Half Portion.

FINAL OUTPUT.

Deleting the Over-Lapping Surfaces from the Light region and Grill portions.Single Cons errors been rectified.

• GRILLS.

In the Grill region deleting the Overlapping Surfaces, then with the help of PASTE/EXTEND option Changing SINGLE cons into Triple cons and deleting the Each Surfaces after that creating the faces with the face options Respectively.

FINAL OUTPUT.

• GRILL TWO.

FINAL OUTPUT.

• GRILL THIRD.

FINAL OUTPUT.

• BMW LOGO .

• WINDOWS

• BODY.

Start with the DOOR region, delete the Overlapping Surfaces, the we can able to see the Single Cons present over there to come EXTEND TOOL is very much used then Patch the surfaces with the Face Options.

• REAR-VIEW MIRROR.

FINAL OUTPUT.

• RIMS AND TYRES.

We can able to see Surfaces are interacting with the Tyres which causes the major errors while creating the Single Volume through Out geometric so, need to delete the surfaces which is been interacting over there. To delete the those Surfaces, we can delete the entire Bottom Portion of the body can create new ones with the face options. Important thing is to keep deleted surface point. CONSTRUCT Option CONS2CURVES options is Used for Reference points.

FINAL OUTPUT.

• GEOMETRY CHECKS.

After Finishing the TOPO-CLEANUP, geometric check is must. CHECK MANAGER `rarr` GEOMETRY `rarr` EXECUTE. In such a way we can able to check whether any Single or Triples cons Present.

ERRORS.

Errors been found (TRIPLE CONS) in the LOGO, BODY and GRILL portions. Finally we rectified those errors.

Now, again checked the Geometry, there is no triples cons present,those single cons nothing but the half portion of the car. Topoclean up is done.

• BOUNDARY CONDITIONS.

Assigning PIDs

BEFORE

AFTER

• MESHING

A Mesh is a network that is formed of cells and points. It can have almost any shape in any size and is used to solve the PDEs (Partial Differential Equation). Each cell of the mesh represent an individual solution of equation which, when combined for the whole network, results in a solution for entire mesh.

SURFACE MESH.

A surface Mesh is a representation of each individual Surface Constituting the Volume mesh. It consists of FACES and VERTICES. Depending on the Pre-processing Software, feature Curves also included. Generally, a Surface Mesh should not have Free edges, and the edges should not be shared by two triangles.

The Surfaces should contain the following qualities of triangles faces.

• Equilateral Sized Triangles
• No Sharp angles with the triangle Sphere
• Gradual Variation in triangle Size from one to the next.
• Surface Mesh generation process should be considered carefully. It has the Direct influence on the quality of the resulting Volume mesh and the effort it takes to get to this step.

SOLID MESH.

Solid Mesh, also known as volume mesh, is a polygonal Mesh representation of the interior Volume Of an Object. There are different types of meshing models that can be used to generate a volume mesh from a well prepared surface mesh.

Three Types of Meshing models are follows,

• TETRAHEDRAL - Tetrahedral cell shape based core mesh.
• POLYHEDRAL - Polyhedral cell shape based core mesh.
• TRIMMED - Trimmed hexahedarl cell shape core mesh.

Once the volume mesh has been built, It can be checked for errors and exported to the other packages if desired.

SIGNIFICANCE OF MESH.

• The mesh influences the Accuracy, Convergence, and Speed of the Simulation.
• In this Process, the continuous geometric space of an objectis broken down into thousands or more of elements to properly define the physical shape of the Object.
• A Good quality Mesh gives more precise results, whereelse a poor Mesh can results in Convergence difficulties, which leads to incorrect results and flase conclusion.

• LOGO MESHING.

TARGET LENGTH	1mm
MINIMUM LENGTH	0.2
MAXIMUM LENGTH	2
ELEMENT TYPE	Trias
MESH MODE	CFD Mesh
OFF ELEMENT	37
OFF ELEMENT CLEARED	Yes.
NUMBER OF ELEMENTS	4572

To Clear the OFF ELEMENTS `rarr` RECONSTRUCT option is Used.

SKEWNESS cleared.

GRILLS.

TARGET LENGTH	1mm
MINIMUM LENGTH	0.2
MAXIMUM LENGTH	2
ELEMENT TYPE	Trias
MESH MODE	CFD Mesh
OFF ELEMENT	2260
OFF ELEMENT CLEARED	Yes.
NUMBER OF ELEMENTS	96251

• WINDOWS.

TARGET LENGTH	2mm
MINIMUM LENGTH	1
MAXIMUM LENGTH	4
ELEMENT TYPE	Trias
MESH MODE	CFD Mesh
OFF ELEMENT	6796
OFF ELEMENT CLEARED	Yes.
NUMBER OF ELEMENTS	29441

After finishing Mesh regions Freeze Option is Used to freeze the meshed parts so that mesh will not be collide into the other parts.

• FRONT/REAR LIGHT

TARGET LENGTH	4mm
MINIMUM LENGTH	3
MAXIMUM LENGTH	10
ELEMENT TYPE	Trias
MESH MODE	CFD Mesh
OFF ELEMENT	113
OFF ELEMENT CLEARED	Yes.
NUMBER OF ELEMENTS	1197

• RIMS/TYRES

TARGET LENGTH	4mm
MINIMUM LENGTH	3
MAXIMUM LENGTH	10
ELEMENT TYPE	Trias
MESH MODE	CFD Mesh
OFF ELEMENT	2797
OFF ELEMENT CLEARED	Yes.
NUMBER OF ELEMENTS	144514

• SILENCER

TARGET LENGTH	3mm
MINIMUM LENGTH	1
MAXIMUM LENGTH	5
ELEMENT TYPE	Trias
MESH MODE	CFD Mesh
OFF ELEMENT	276
OFF ELEMENT CLEARED	Yes.
NUMBER OF ELEMENTS	8576

• REAR VIEW MIRROR.

TARGET LENGTH	2mm
MINIMUM LENGTH	0.5
MAXIMUM LENGTH	3
ELEMENT TYPE	Trias
MESH MODE	CFD Mesh
OFF ELEMENT	368
OFF ELEMENT CLEARED	Yes.
NUMBER OF ELEMENTS	4428

• BODY

TARGET LENGTH	3mm
MINIMUM LENGTH	1
MAXIMUM LENGTH	5
ELEMENT TYPE	Trias
MESH MODE	CFD Mesh
OFF ELEMENT	22636
OFF ELEMENT CLEARED	Yes.
NUMBER OF ELEMENTS	168943

• HALF PORTION BMW CAR

NUMBER OF ELEMENTS - 441482

After Finishing Mesh go to transform tool choose copy option then choose 3point mirror and click any 3 corordinates. The other Half portion is created and geometric is completed. Then we need again check any single cons are present, if present need to be rectified.

TRANFORM `rarr`3 POINT MIRROR.

• WIND TUNNEL.

Now, Creating the Wind Tunnel to create the tunnel we need to measure the car first. Then Length Of the Wind tunnel from the Front car should be 4x, Rear End 6x, Height should be 3x.

TOTAL LENGTH OF THE CAR - 1300.

DIRECTIONS.

FINAL OUTPUT.

CONCLUSION.

• Geometric Errors like Single Cons, Triple Cons, missing Surfaces and Over lapping surfaces are identified and rectified those in errors in BMW Model.
• While Working in this challenge faced many difficulties specially in the Grills portions and learned different tools, and how to clear the OFF ELEMENTS and learned how over come those difficulties.
• Learned about Dimensions of the Wind tunnel and how to create these tunnels.
• Hence we can come to conclude that the Surface Meshing and creating Wind tunnel is done and results are satisfied.