Hey @harryfeng,
Thanks for reaching out on the Forum.
The mesh intersection seems to be caused by self-intersection as mentioned in the error you are getting:
You can read more about this error here: Surface Meshing Self-Intersection | Knowledge Base | SimScale
Maybe try keeping a small gap between the flow region face and the wheel of the car geometry and meshing it again?
Let us know how it works out for you!
Best,
Satvik