The 2D car

As our last study case we tried to make a mesh of a 2D car. This work is inspired by the ICEM tutorial, but we invented our own geometry.

We build the DDN geometry by placing 46 points and by linking them with straight lines, the lines were then converted into B-splines. The entire domain is 20m in height and 40m and length. The car front is placed at 10m of the inlet at is 4,5m long and 1,4m high. We meshed it with hexa using approx. 10 cm elements for a total of 70 000 elements. The mesh can still be improved at this moment and must be considered as a first try at this time.

A view of the complete mesh. The number of elements far from the car can be greatly reduced.

A close-up view of the mesh near the car. The overall meshing strategy is acceptable, the size of the elements very close to the car should be smaller.

We had some problem making the mesh run with Fluent. Our difficulty was finally overcome using a little trick: we exported the mesh as an IDEAS file under ICEM, we then imported that file into Fluent. We then made a computation using air coming from the inlet at the left with a speed of 50m/s (approx. 180km/h). The Reynolds value is then approx. 7.10e6. We used a K-E model.

We used Fluent to refine the mesh around the car.

We can take a look at the velocity:

We can see the effect of the windshield quite clearly. The speed reaches over 250 km/h in that region. The size of the boundary layer is probably to big and should be improved by taking smaller elements width.

This is a wider view of the velocity field. We can see that the car's effect extends far over (over 5m) and behind the car (over 10m).

We can draw the velocity vectors:

We can see distinguishably two recalculating zone behind the vehicle.

A close-up of the back of the car makes them easier to see.

The path line are also worth a look:

On this image particles start from the car surface.

We can also look at the pressure:

Finally we can look the value of K:

K is concentrated in a small area behind the vehicle.