Week 4 Challenge : CFD Meshing for BMW car

AIM: To perform INTERNAL ANALYSIS on WIND TUNNEL with given model present in it. Has to perform Pre-Processing of CFD which is required on given model and on wind tunnel viz; Geometry Cleanup, Surface Meshing and Volumetric Meshing on given Wind tunnel.

(#WIND TUNNEL WORKING PRINCIPLE

How Do Wind Tunnels Work?
Wind tunnels usually have powerful fans to move the air through the tube. The object being tested is placed in the tunnel so that it will not move. The air moving around the still object shows what would happen if the object were moving through the air. The object can be a smaller-scale model of a vehicle, one piece of a vehicle, a full-size aircraft or spacecraft, or even a common object like a tennis ball. Usually, the object carries special instruments to measure the forces produced by the air on the object. Engineers also study how the air moves around the object by injecting smoke or dye into the tunnel and photographing its motion around the object. Improving the flow of air around an object can increase its lift and decrease its drag.

Data Taken From:https://www.nasa.gov/audience/forstudents/5-8/features/nasa-knows/what-are-wind-tunnels-58.html

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PROCEDURE: It is clear from the working principle that to perform internal analysis of Tunnel with given model in it, we need to isolate the given model in such a way that the whole model should be made as a single volume at the stage of Geometry cleanup of the model. There is no need of Internal analysis of given model. Here I did only EXTERNAL analysis of it as it suffice the procedure.

So, I divided the whole process into stages.

STAGE 1: Procedures on given model (BMW M6-CAR).

a) GEOMETRY CLEANUP

b) SURFACE MESHING

STAGE 2: Procedures on Wind Tunnel.

a) Creation of Wind Tunnel with required Boundary conditions

b) GEOMETRY CLEANUP (Needed)

c) SURFACE MESHING

d) VOLUMETRIC MESHING

STAGE 1: Procedures on given model (BMW M6-CAR).

a) GEOMETRY CLEANUP: By observing the given model, came to a coclusion that it is a Axisymmetric body. If we cut the body at centre it is easy to perform the needed work and later we can mirror the body. As it is axisymmetric no change of parts will be there. So, I divide the whole Geometry into two halves.

Performed Geometric analysis using CHECKS MANAGER>GEOMETRY CHECKS in TOOLS feature.Found penetration and geometrical errors in the model.Performed needed cleanup and assigned PIDs for different sections based on the classifaction of working principle.

On Grills:

Found penetrations and multiple volumes in it. As our main aim is to make the car as single volume, made adjustments to the model and made it as a part of single volume. For this used TOPO > FACES , HOT POINTs, CONS, CURVES>CONS2CURVE tools followed by suitable tools within it.

b) Surface Meshing

For GRILLS and LOGO as per the given instructions taken the tria element, with target size of 1mm, min/max length as 0.5/1.2mm in mesh quality parameters respectively. Used CLASSIC MESH>PARAMETERS>SPACING >AUTO CFD algorithm for spacing elements. For mesh Generation used MESH GENERATION> CFD>VISIBLE algorithm as it gives better results.

As these parts are given different perimeters for the compliance different meshing elements used MACROS>FREEZE option.

For Rims and Tyres ,Optical Rear view mirror ,Window as per the given instructions taken the tria element, with target size of 2mm, min/max length as 2.5/1.5mm in mesh quality parameters respectively. Used CLASSIC MESH>PARAMETERS>SPACING >AUTO CFD algorithm for spacing elements. For mesh Generation used MESH GENERATION> CFD>VISIBLE algorithm as it gives better results.

As these parts are given different perimeters for the compliance different meshing elements used MACROS>FREEZE option.

For silencer and body of the car as per the given instructions taken the tria element, with target size of 3mm, min/max length as 2.5/3.5mm in mesh quality parameters respectively. Used CLASSIC MESH>PARAMETERS>SPACING >AUTO CFD algorithm for spacing elements. For mesh Generation used MESH GENERATION> CFD>VISIBLE algorithm as it gives better results.

As these parts are given different perimeters for the compliance different meshing elements used MACROS>FREEZE option.

For Lights as per the given instructions taken the tria element, with target size of 4mm, min/max length as 3.5/4.5mm in mesh quality parameters respectively. Used CLASSIC MESH>PARAMETERS>SPACING >AUTO CFD algorithm for spacing elements. For mesh Generation used MESH GENERATION> CFD>VISIBLE algorithm as it gives better results.

Satisfactory with meshing.

now all parts are meshed and assigned PIDs. After that UNFROZE all parts with MACROS>UNFREEZE.

used TRANSFORM>COPY>SYMMETRY>3 POINT SELECTION and Mirrored car.

As it is complex geometry used QUALITY parameters like skewness and min and max length options

Found OFF ELEMENTS tried GRID>MOVE option from CLASSIC MESH unable clear it. Tried to IMPROVE by using RESCONSTRUCT , RESHAPE unable to perform it.

STAGE 2: WIND TUNNEL creation

Based on length and width of car constructed a box shaped wind tunnel with certain dimension.All are in mm.

car dimension is 1306 mm. Taken X as approx 1300.

From front face of 650+4*1300=5850

From back face 650+6*1300=8450

on Sides=365+3*1300=1665

On bottom =500

On top=500+3*1300+350=4750.

Created box shaped tunnel.

Meshed with bottom face as 20mm and top face as min/max 30/10mm, 100mm min/max 90/110 with growing element size.

Found satisfactory with results.

CONCLUSION:

My mesh contain off elements of numbered 141 elements, hence it is low quality mesh.

NOTE Unable to upload ANSA file, attaching STEP file.