is it possible to do the cfd analysis of a surface modelled 3d car?
You can model in surface and convert it into solid (Thicken feature), then do the CFD analysis....I tried to do external CFD for a simple surface..... If it is not a solid, and is just a surface, then solidworks wont accept for CFD.... (As far as I have seen)!!!!
Answered with a tutorial: https://grabcad.com/tutorials/is-it-possible-to-do-the-cfd-analysis-of-a-surface-modelled-3d-car
I think that happens because you are trying a 3d analysis to a 2d object. Try giving it a third dimension with knit and thicken so it can convert a surface model to solid CFD. Knitting the car surfaces together will do the job there, I think.
As for the CFD analysis, keep in mind that even though it's really easy to do a cfd analysis, it's really hard to get reliable results. Expect the downforce (lift) to be 20-30% smaller and the Drag 2 to 3 times bigger than expected. Message me if you need any hints when you get there.
You might try to split the surfaces to simpler surfaces and use thicken feature on these surfaces separately to get separate solid bodies.. Then use boolean feature appropriately to get your final solid abject. Try this method, and let me know the results of it...