Most CFD guys have aerospace engineering/physics backgrounds, not CS. Trust me, the coding is the EASIEST part of the field. It's almost an afterthought. CFD development, at the level where you are contributing novel work, is applied math. Nothing more, nothing less.

OP, your aspiration is possible but difficult. CFD is a rarefied field of heads-down, highly quantitative minds. If you were outstanding at math in HS then I say go for it. Going back to undergrad isn't a bad idea. You'd be a non-traditional student, but I knew a few of those when I was in undergrad who did well. You should be pretty comfortable in math through vector calculus and linear algebra; if you're really struggling, you might want to reconsider paths. You have to be ready for 3-4 years of hardcore aerospace engineering and math courses, which could be a tough transition. Good luck.