Week 4 Challenge : CFD Meshing for BMW car

OBJECTIVE:

The main of the challenge is to mesh the surface of BMW car and perform geometry clean up by using ANSA software and create a wind tunnel for CFD analysis

PROCEDURE:

• GEOMETRY CLEAN UP
• ASSIGNING RELEVANT PID's
• SURFACE MESHING
• PERFORM SYMMETRY
• CREATION OF WIND TUNNEL

1. GEOMETRY CLEAN UP:

• Open the given IGS file in ANSA software and it shows the wire frame model
• Enable the shadow mode and it shows the 3-D figure and keep the model in PID mode
• Enable all the cons and cross hatches to perform geometry clean up and also goto MESH -> PARAMETERS -> LENGTH and keep the length as 1mm to have smooth curve

• Perform geometry clean up on side parts of car

GEOMETRY CLEAN UP OF SIDE GRILL:

• First to perform geometry clean up for SIDE GRILL we have to isolate the part and lock it by using NOT mode and LOCK mode
• We have to delete the unnecessary surfaces on the grill
• Goto FACES -> CUT and enable the parametric cut and then cut the fins those are present on the grill
• Perform to all fins and remove the unwanted surface
• Goto FACES -> NEW -> COONS /FITTED to join the deleted surfaces by using these options and the geometry clean up is completed

• Delete the half part of the car and perform the geometry clean up for remaining parts

GEOMETRY CLEAN UP FOR BOTTOM GRILl AND INTAKE GRILL:

• First to perform geometry clean up for BOTTOM GRILL we have to isolate the part and lock it by using NOT mode and LOCK mode
• Primarily we have to delete the unwanted surfaces by using DELETE option and make sure it is in ENT mode
• Goto CONS -> PROJECT and project the cons of the grills onto surface and delete the unwanted surfaces
• Sometimes we can create the new surface by deleting the old surface according to our necessity
• Goto FACES -> NEW -> COONS /FITTED to join the deleted surfaces by using these options and the geometry clean up is completed
• Perform similar operations on the INTAKE GRILL

GEOMETRY CLEAN UP FOR BOTTOM SURFACE AND TYRES:

• First isolate the tyres by using NOT and LOCK Mode
• Then remove one of the tyres because it has more errorrs and we cannot recitfy and we can replicate the part by using SYMMETRY option
• Goto CONS -> PROJECT and project the cons of circles of tyres onto rims
• Then DELETE the common surface present in between tyres and rims
• Thus geometry clean up of tyres is completed
• Remove the unwanted surface on bottom part and also not assosiated with wheels
• Perform operations for EXHAUST also
• Perform same operations as mentioned above and complete the geometry clean up
• After performing geometry clean up for all parts perform geometry check up by hiding single cons

ASSIGNING RELEVANT PID's:

• To assign PID's for given figure goto PID MANAGER tool
• It shows all the PID's assigned to the figure
• First islote the body and lock the figure.Then goto -> PROPERTIES it shows the PID's assigned to body so we have to rename as BODY by creating new PID
• Repeat the same process and assign PID's to all all parts of the car

SURFACE MESH:

• Mesh the surface according to the given parameters

Body = 3mm

Grills = 1mm

Lights = 4mm

Tyres and Rims = 2mm

ORVM = 2mm

Windows = 2mm

Silencer = 3mm

Logo = 1mm

• Goto MESH -> PERIMETERS -> LENGTH and mesh the surface
• Use TRIA elements and the mode of mesh is FREE mesh
• After the surface mesh checks can be done and eliminate the errors occured in mesh model

ELIMINATION OF SKEWNESS, MIN LENGTH AND MAX LENGTH ERRORS:

• Goto mesh quality criteria and adjust the parameters to standard values
• In our model MIN LENGTH = 1mm so the limit is set to 0.2 mm and MAX LENGTH = 4mm so it is set to 5mm
• Apply the changes and the errors are appeared on the left side of the screen and we have to eliminate those errors and it shown as OFF elements
• Goto SHELL MESH -> RECONSTRUCT to reconstruct the model to eliminate min length and max length errors and make sure that the elemnts are within our limits
• To find skewness error goto skewness and right click then click on show only it will show only skewness error
• These error is rectified by using GRIDS -> MV SURF option or GRIDS -> PASTE options and also by reconstructing the structure
• After eliminating all errors it shows OFF ELEMENTS is zero

SYMMETRY:

• Goto TOPO mode and perform the symmetry operation for the model
• First we have to isolate tyres and lock the remaining model
• Goto SYMMETRY -> COPY and copy the entire model and select the MIRROR 3 POINT PLANE and select three nodes then it replicates the other image
• For safety use TOPO option to make all cons to double cons by selecting the entire modell
• In order to perform symmetry on front tyre goto POINTS -> ON COG to locate the centre part of tire and use undelete option to retrieve some part of tire and locate mid point of other tire
• Perform symmetry Operation by copying tyre and translation using two nodes
• Change the threads on right side tyres using same option

CREATION OF WIND TUNNEL:

• To create the wind tunnel first calculate the length of car
• Then goto -> POINTS -> NEW and create points in all directions according to the directions of wind tunnel
• Create three nodes that is responsible to draw a plane
• Goto surfaces -> PLANE and draw a plane using those three nodes and replicate the same plane using translation symmetry
• Repeat the same procedure for other two sides
• Goto CONS-> INTERSECT to intersect all planes and delete the unwanted surfaces
• Thus wind tunnel is created and assign PID's to differentiate INLET and OUTLET

MESH OF WIND TUNNEL SURFACE LINES:

• Sides of bottom of tunnel of length 20mm
• Sides of front and back as of length 50mm
• Sides of top of tunnel of length 100mm
• Then goto PERIMETERS -> SPACING -> CONSTANT LENGth and assign min value as 20mm and max as 100mm and assign to all front and back sides

CONCLUSION:

• Geometry clean up is done step by step procedure
• Assigning PID's is also completed
• Surface mesh is performed and elimination of errors is successful
• Perform symmetry is also done by applying different options ( like Translation , Mirror 3 point plane )
• Replicating threads on right side tyres is also done using symmetry
• Mesh quality errors is eliminated by using different tools to achieve better model
• Creation of wind tunnel is also completed by assigning different parameters